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Michigan State
University

 

 

 

This is to certify that the
thesis entitled
Continuous Loading-multiple Size Cohort Management

Versus Single-size Cohort Management in the
Culture of Yellow Perch (Perca flavescens)

 

presented by

Steven Daniel Hart

has been accepted towards fulﬁllment
of the requirements for

M.S. Fish. & Wildl.

 

 

degree in

 

Date December 13, 2001

 

0-7 639 MS U is an Afﬁrmative Action/Equal Opportunity Institution

PLACE IN RETURN BOX to remove this checkout from your record.
To AVOID FINES return on or before date due.
MAY BE RECALLED with earlier due date if requested.

 

DATE DUE

DATE DUE

DATE DUE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

6m cJCIRC/DatoDuepes—ms

 

 

CONTINUOUS LOADING-MULTIPLE SIZE COHORT MANAGEMENT VERSUS
SINGLE-SIZE COHORT MANAGEMENT IN THE CULTURING OFYELLOW
PERCH (PERCA FLAVESCSENS)

 

By

Steven Daniel Hart

A THESIS
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of
MASTER OF SCIENCE
Department of Fisheries and Wildlife

2001

ABSTRACT
CONTINUOUS LOADING-MULTIPLE SIZE COHORT MANAGEMENT VERSUS

SINGLE-SIZE COHORT MANAGEMENT IN THE CULTURING OF YELLOW
PERCH (PERCA FLAVESCSENS)

By

Steven Daniel Hart

Commercial yellow perch aquaculturists have used continuous loading-
multiple cohort management and single-size cohort management. Continuous
loading-multiple size cohort management is the replacement of harvested market
size ﬁsh with ﬁngerlings in a single tank system. Single-size cohort management
is the harvesting of the entire production system prior to restocking ﬁngerlings.
Studies were designed to determine: 1) if yellow perch in continuous loading-
multiple cohort systems grew signiﬁcantly different than yellow perch in single-
size cohort systems, 2) if female yellow perch grew at a signiﬁcantly different rate
than male yellow perch in both management systems. Small- and large-size
females and large-size males in single-size cohorts grew at the same rate as
their counterparts in mixed-size cohorts. Small-size males in mixed-size cohorts
grew at a signiﬁcantly higher rate than small-size males in single-size cohorts
and were not signiﬁcantly smaller than large-size males at the end of the
experiment. Large- and small-size females in both single- and mixed-size
cohorts were signiﬁcantly larger than large- and small-size males within single-

and mixed-size cohorts.

DEDICATION

To my grandmother and late grandfather, without them I would have never
attended college. This is for both of you. I love you.

iii

ACKNOWLEDGEMENTS

I would like to thank Dr. Donald Garling, Dr. Ted Batterson and Dr.
Richard Snider for their guidance while serving as my graduate committee for my
Master’s degree program. I extend particular thanks to Dr. Garling for giving me
the opportunity to work on this project and for being a close personal friend
whose touch to my life extends far beyond the scope of this degree.

The North Central Regional Aquaculture Center provided the primary
source of funding for this project. Bay Port Aquaculture Systems and Paragon
Aquaculture assisted with this project by providing ﬁsh and starting data.

I would also like to thank Jon Amberg, Amin Maredia, Dave Haley, Chris
Rees, Jerrie Nichols and Chris Starr for their assistance and friendship
throughout this project. Special thanks are extended to Jon Amberg for his
assistance, friendship and willingness to provide me with a place to live when I
first came to MSU.

I would like to thank Dr. Thomas Coon for his guidance when I was an
undergraduate and graduate student. I would like to thank Dr. Nathalie Trottier,
Bob Burnett, Dave Main and Pao Ku in the Animal Science Department for their
assistance with proximate analysis. I would also like to thank Dr. Scott
Winterstein for his willingness to share his statistical expertise and Dr. Weiming

Li for his willingness to share his physiological expertise.

iv

I would like to thank my parents, Cathy Wood, Richard and Felicia Hart
and my best friends, Steve Dailey and Chris Plummer for putting up with me
during this adventure.

Finally and most importantly, I want to thank my lovely wife, Stephanie,
who I met and wed during this project, for her love and support. I love her more
than anything and look forward to our many years together. I would also like to
thank her for carrying our unborn child, Jeffrey Logan Hart, who I cannot wait to

see for the ﬁrst time.

TABLE OF CONTENTS

LIST OF TABLES ..................................................................

LIST OF FIGURES ................................................................

INTRODUCTION ...................................................................

LITERATURE REVIEW ...........................................................

A.
B.
C.

Yellow perch culture methods .....................................
Gender related growth differences ...............................
Single-size versus multiple-size cohorts ........................

MATERIALS AND METHODS ...................................................

A.
B.
C.
D.

MSU Culture Facilities and RAS ...................................
Experimental design ..................................................
Proximate analysis ....................................................
Statistical analysis ....................................................

RESULTS .............................................................................

A.
B.
C.
D.
E.

Total tank weight ......................................................
Gender distribution ....................................................
Final size difference by cohort and gender .....................
Proximate analysis ...................................................

Water quality parameters and mortalities .......................

DISCUSSION ........................................................................

WWPQW?

Objective 1 ...............................................................
Objective 2 ..............................................................
Initial tank weight ......................................................
Regression analysis ................................................
Proximate analysis ..................................................
Objective 3 ..............................................................

SUMMARY AND CONCLUSIONS .............................................

REFERENCES .....................................................................

vi

vii

viii

13
16

22
22
25
28
28

30
31
33
37
37
48

51
51
52
53

55
58

61

64

LIST OF TABLES

Table 1. A summary of total tank weight (9) over 9-month
experiment. SS = Single-Size Small Cohort, SL = Single-Size
Large Cohort, M = Mixed-Size Cohort. .....................................

Table 2. Final mean lengths (mm) and weights (9) of yellow perch
by gender and cohort. SS = Single-Size Small Cohort, SL =
Single-Size Large Cohort, MS = Small Fish Within Mixed Size
Cohort, ML = Large Fish Within Mixed-Size Cohort.
Corresponding letters indicate no signiﬁcant difference between
means, P > 0.05. .................................................................

Table 3. Proximate analysis, on a dry matter basis, for yellow
perch fed 2% total body weight for 9 months. SFS = Small
Females Single Cohort, SMS = Small Males Single Cohort, LFS =
Large Females Single Cohort, LMS = Large Males Single Cohort,
LFM = Large Females Mixed Cohort, LMM = Large Males Mixed
Cohort, SFM = Small Females Mixed Cohort, SMM = Small Males
Mixed Cohort. .....................................................................

Table 4. Wet weight (g) of mortalities and replacement ﬁsh. .........

Vii

32

36

47

50

LIST OF FIGURES

Figure 1. Conceptual ﬂow diagram of the RAS used in experiment
with close-up of culture tank design .......................................

Figure 2. Growth of large single-size cohort over nine month
experiment. Linear regression equation predicts the cohort would
have reached market size 135 days (4.5 months) after completion
of grow-out trial assuming continued linear growth.

Figure 3. Growth of small single-size cohort over nine month
experiment. Linear regression equation predicts the cohort would
have reached market size 258 days (8.5 months) after completion
of grow-out trial assuming continued linear growth.

Figure 4. Final mean weight and standard deviation of large-size
females within single- and mixed-size cohorts. Values were not
signiﬁcantly different, P > 0.05. ..............................................

Figure 5. Final mean weight and standard deviation of small-size
females within single- and mixed-size cohorts. Values were not
signiﬁcantly different, P > 0.05. ..............................................

Figure 6. Final mean weight and standard deviation of large-size
males within single- and mixed-size cohorts. Values were not
signiﬁcantly different, P > 0.05. ..............................................

Figure 7. Final mean weight and standard deviation of small-size
males within single- and mixed-size cohorts. Small-size males in
mixed-size cohorts were signiﬁcantly larger than small-size males
in single-size cohorts, P < 0.05. .............................................

Figure 8. Final mean weight and standard deviation of large and
small-size males within mixed-size cohorts. Values were not
signiﬁcantly different, P > 0.05. ..............................................

Figure 9. Final mean weight and standard deviation of large-size

females and males within single-size cohorts. Females were
signiﬁcantly larger than males, P < 0.05. .................................

viii

24

35

38

39

4O

41

42

43

Figure 10. Final mean weight and standard deviation of large-size
females and males within mixed-size cohorts. Females were
signiﬁcantly larger than males, P < 0.05. .................................. 44

Figure 11. Final mean weight and standard deviation of small-size
females and males within single-size cohorts. Females were
signiﬁcantly larger than males, P < 0.05. ................................... 45

Figure 12. Final mean weight and standard deviation of small-size

females and males within mixed-size cohorts. Females were
signiﬁcantly larger than males, P < 0.05. ................................... 46

ix

INTRODUCTION

Consumer demand for yellow perch (Perca ﬂavescens) in the Great Lakes
region has historically been high (Calbert 1975). Yellow perch are the primary
ﬁsh used for Friday-night fish fries (Lesser and Vilstrup 1979). Demand for
yellow perch ﬁllets by restaurateurs and homemakers is high because of the
ﬁsh’s ﬁrm ﬂesh and low fat content (Lindsay 1980), the lack of cooking odor, and
the non-ﬁshy taste of the ﬁllet.

The market demand for yellow perch has not been met by commercial
ﬁshing harvests since the early 1970’s (Calbert 1975). Wild stocks of yellow
perch have declined in all Great Lakes” waters, including Lake Michigan, Lake
Erie, and Saginaw Bay (e.g., Belonger 1986), leading to prohibitions on
commercial harvesting in Lake Michigan (except Green Bay) and regulations
limiting total catch in other Great Lakes’ waters. Diminishing commercial supply
has caused prices for yellow perch ﬁllets to climb for over a decade (Reipe
1997)

Interest in commercial aquaculture production of yellow perch has
increased because of the decline in harvested wild stocks (Calbert 1975; Downs
and Smith 1983). The North Central Regional Aquaculture Center (NCRAC) has
recognized interest in yellow perch aquaculture and focused research funding to
develop culture techniques for commercial production. Research has been

conducted to improve larval culture, grow-out strategies, brood-stock

management, and nutritional requirements of yellow perch (NCRAC 1991;
NCRAC 1996).

The ability of Recirculating aquaculture systems (RAS) to provide year-
round conditions for optimal growth has been of particular interest (Heidinger and
Kayes 1986). RAS technology has been used to provide optimal conditions for
yellow perch growth. Calbert and Huh (1976) cultured 15 g (0.5 oz) yellow perch
ﬁngertings and grew them to market size in 9 to 11 months using small-scale
RAS. Major concerns have arisen about the economic feasibility of raising yellow
perch with RAS techniques. Models of small-scale RAS have shown that they
are not economically proﬁtable (Kocurek 1979; Lipscomb 1995). RAS
techniques need to be developed that will allow commercial aquaculture to
produce a proﬁt.

Yellow perch culturists use two types of grow-out strategies: single-size
cohorts and continuous loading-multiple size cohorts. In single-size cohort
management, ﬁsh are harvested when they attain market size. The grow-out
system is not restocked until all of the ﬁsh are harvested. ln continuous loading-
multiple size cohort management, market size ﬁsh are harvested from a
production system and replaced with smaller size ﬁsh. Continuous loading-
multiple size cohort management has been used to allow for multiple harvests
throughout the year from a single culture tank (Mike Libbin, Paragon
Aquaculture, personal communication).

Multiple harvests from one grow-out system have allowed commercial

catﬁsh producers to generate a steady source of income by supplying fresh ﬁsh

to their market throughout the year (Busch 1985). However, variations in ﬁsh
size have been observed because of competition between large and small ﬁsh
for food (Collier and Schwedler (1990) and because of differences in feed
conversion ratios (Busch 1985). Busch (1985) indicated that feed conversion
ratios (weight of feed fed/weight gain of ﬁsh) were lower in channel catﬁsh reared
in single-size cohorts (1.61 feed conversion) than in channel catﬁsh reared in
continuous loading-multiple size cohorts (2.05 feed conversion).

Commercial producers of yellow perch have used variations of continuous
loading-multiple cohort management. This management strategy has not been
evaluated for yellow perch aquaculture. Concerns about this technique have
been expressed because female perch grow faster than males (Malison et al.
1985). Initial harvests of market-size perch from a continuous loading-multiple
cohort grow-out system would have been expected to be predominately female
because they have been shown to grow faster than males (Malison et al. 1985).
Harvested ﬁsh would have been replaced with ﬁngerlings, expected to exhibit a
50:50 gender distribution. As market-size ﬁsh were continuously harvested from
the grow-out system, slower growing males would have been expected to come
to dominate the grow-out system over time.

Feed management is an additional concern when using continuous
loading-multiple cohort management. Size variation of ﬁsh present in a grow-out
system has caused problems with feeding the correct pellet size (Hardy 1989).
Feed pellets that were too large for a ﬁsh caused an increase in feed waste as

the ﬁsh needed to wait until the pellet broke down to a size small enough to

consume (Hardy 1989). As the pellet broke down in size, nutrients were lost into
the system (Hardy 1989). Pellets that were too small resulted in wasted feed and
increased nutrient leaching because of the increased surface area to volume
ratio in small feeds compared to larger feeds (Hardy 1989).

This research project was designed to evaluate growth and performance
of yellow perch using continuous loading-multiple size cohort management and
single-size cohort management strategies. This experiment was part of a larger
cooperative project that included commercial cooperators (Paragon Aquaculture
and Bay Port Aquaculture Systems, Inc.), the University of Wisconsin-Superior
Sea Grant Institute, and Michigan State University (MSU).

Bay Port Aquaculture Systems, Inc. (West Olive, MI) was to conduct
single-size cohort management with yellow perch in a RAS on a commercial
scale. Paragon Aquaculture (Oshkosh, WI) was to conduct continuous loading-
multiple cohort management with yellow perch in a RAS on a commercial scale.
Bay Port was not able to perform their part of the project due, in part, to a near
100% ﬁsh kill from chlorine toxicity caused by a faulty chlorine treatment by
Consumers Energy, Bay Port’s main source of water supply. Paragon was not
able to complete their portion of the project because they went out of business
during the ﬁrst year of the project. They purchased ﬁsh with a disease of
unknown origin, causing a near 100% ﬁsh kill in their grow-out system.

The University of Wisconsin-Superior Sea Grant Institute was to conduct
break-even analysis for yellow perch aquaculture. They were not able to

complete their portion of the project because of insufﬁcient data supplied by

commercial yellow perch producers. Michigan State University conducted an
evaluation of single-size cohort management and continuous loading-multiple
size cohort management strategies on an experimental scale. MSU researchers
were to assist both commercial operators in the collection and statistical analysis
of data from the commercial-scale projects. Results from the commercial
producers were to be compared to MSU's small-scale experimental results.
However, MSU was the only cooperator able to complete their portion of the

project.

OBJECTIVES:

1. To determine whether continuous loading-multiple size cohort management
or single-size cohort management was more productive in terms of growth for
yellow perch aquaculture.

Null Hypothesis 1: Growth of yellow perch using continuous loading-multiple
size cohort management versus single-size cohort management was equal.

2. To determine gender and size distribution of yellow perch throughout all
experiments.

Null Hypothesis 2: Growth of male yellow perch was equal to growth of
female yellow perch.

3. To determine if additional experiments comparing continuous loading-multiple
cohort management versus single-size cohort management should be
performed to develop new management techniques for yellow perch

aquaculture. The results of the continuous loading-multiple size cohort

management or single-size cohort management research project should be

used as a starting point to determine what further research is necessary.

LITERATURE REVIEW

The commercial supply of yellow perch has been unable to meet the
market demand since the early 1970’s (Calbert 1975). The commercial ﬁshery
has been limited by regulatory constraints due to the declining stocks in all Great
Lakes’ waters, including Lake Michigan, Lake Erie, and Saginaw Bay (e.g.,
Belonger 1986). The Lake Michigan ﬁshery was historically one of the highest
producers of yellow perch. Recruitment of yellow perch in Lake Michigan has
been virtually non-existent since 1989 (M. Keniry, Wisconsin Department of
Natural Resources, personal communication). As a result of the problem
ﬁsheries managers have closed the commercial perch ﬁshery (except in Green
Bay) and decreased recreational bag limits (down from 100 to 5 — 35 ﬁsh/day) by
all states along the border of Lake Michigan (D. Clapp, Michigan Department of
Natural Resources, personal communication). The cause of this problem has not
been determined.

Demand for yellow perch has remained high while supply has diminished
and prices for ﬁllets have continued to climb for over a decade (Reipe 1997).
Increased supply and reduced prices should increase the purchases of yellow
perch ﬁllets. Due to the reduction of supply of wild stocks, the high price of ﬁllets,
and the concern of contaminant levels in Great Lakes ﬁsh (Downs 1985; Smith
1988), interest in yellow perch aquaculture has grown (Calbert 1975; Downs and

Smith 1983).

Yellow perch have shown many characteristics that make it a desirable
species for aquaculture, including: (1) ready acceptance of formulated feeds; (2)
lack of aggressive behavior and cannibalism; and (3) relatively high tolerance of
crowding, handling, and marginal water quality (Heidinger and Kayes 1986).
Studies have shown that yellow perch ﬁllets produced from aquaculture facilities
are similar in taste and quality to those of wild ﬁsh (Lindsay 1980).

There have been aquaculture sites capable of producing ﬁngertings and
food-size yellow perch. Studies have shown that perch can be grown using
many different aquaculture techniques including net-pens, ponds, ﬂow-through
systems and RAS (NCRAC 1994; NCRAC 1996). An economic break-even
analysis of commercial yellow perch producers was to be conducted by the
University of Wisconsin-Superior Sea Grant Institute (NCRAC 1999). The
analysis was not completed due to the commercial producers’ failure to report
economic data due to the termination of operations or failure to reach
commercially viable production levels (NCRAC 1999).

Yellow perch grow relatively slow compared to other food ﬁsh used in
aquaculture. Growth has been shown to signiﬁcantly decrease just before perch
reach market size greater than 150 mm, 5.9 in (Huh 1975; Schott 1980; Malison
et al. 1985). Females have been shown to grow faster and attain larger sizes
than male yellow perch (Scott and Crossman 1973; Schott 1980; Malison et al.
1986) at the onset of sexual maturation and gonadal development which can
occur in the ﬁrst year of life (Malison et al. 1986). Studies on perch (Huh 1975;

Malison et al. 1985), as well as other cultured species such as ﬂatﬁsh and Paciﬁc

salmon (Purdom 1976; Utter et al. 1983), have shown a strong correlation
between sexual maturation and reduced growth, food consumption, and food
utilization efﬁciency

Researchers and aquaculturists in the North Central Region (NCR) have
focused efforts to develop techniques to make yellow perch culture a proﬁtable
business. Brood stock management, intensive larval culture and grow-out
techniques for commercial yellow perch production need further development

(NCRAC 1991; NCRAC 1996).

Yellomrch culture methods

Perch have been grown in the NCR using ponds, net-pens, ﬂow-through
systems and RAS (NCRAC 1991; NCRAC 1994; NCRAC 1999).

Pond grow-out has been commonly used for yellow perch aquaculture
production throughout the NCR. J. A. Malison (personal communication)
reported at the January 2000 Yellow Perch Forum in Hudson, WI, that ponds
stocked with ﬁngerlings have produced up to 4,740 kg/ha (4,229 lbs/acre)
market-size ﬁsh (115 g, 4.76 oz). Malison theorized a maximum yield of 10,000-
kglha was possible.

Pond culture has been popular with perch aquaculturists because the
initial investment associated with constructing pond systems has been lower than
ﬂow-through systems or RAS (Ogle 1991; Kelly 2000; Timmons 2000c). Pond
culture operating costs have been shown to be lower than indoor culture because

of the availability of natural resources such as sunlight and algal production

(Timmons 2000c). Pond production of yellow perch has been shown to be more
economical and produced higher numbers of yellow perch than ﬂow-through or
RAS (Kelly 2000). Currently, approximately 10 yellow perch culturists in
Nebraska and Wisconsin produce food-size ﬁsh in ponds, however it is unknown
whether these enterprises are proﬁtable (Malison 1999).

Optimum growth temperature for yellow perch has been shown to be near
22°C, 72°F (Huh et al 1976; Carlander 1997). The National Weather Service
(NWS 2001) has reported that areas in the southern region (Kansas, Missouri
and Nebraska) of the NCR have only maintained average monthly ambient
temperatures at 22°C (72°F) or higher for a maximum of 3 months out of the
year. Average monthly ambient temperatures less than optimal for perch growth
have led to optimum grow-out lasting 0-3 months per year in ponds in the NCR
(Huh et al 1976; Carlander 1997; NWS 2001). Lethal upper temperatures to
yellow perch have been reported to range from 26 to 30°C, 79 to 86°F (Carlander
1997). States in the Southern Region (except Kentucky and Virginia) have
exhibited ambient temperatures at or above the upper lethal threshold through
part of the year (NWS 2001), making yellow perch pond grow-out in the southern
region less feasible.

Photoperiod has been shown to be more important than temperature to
the growth of young yellow perch (Huh et al. 1976). Sixteen hours of light and 8
hours of dark have been reported as the optimum daily photoperiod for maximum
growth (Huh et al. 1976). Similar photoperiods are not exhibited year-round in
the NCR.

10

Due to the unfavorable weather conditions, ﬁngerlings stocked into ponds
under natural conditions typically have taken 2 to 3 years to reach market size in
the NCR (Heidinger and Kayes 1986). Conditions supporting optimum growth
last for 0-3 months out of the year (Huh et al 1976; Carlander 1997; NWS 2001).
During the remainder of the year, yellow perch stocked in ponds grow at sub-
maximal rates. In addition to unfavorable growing conditions in the NCR through
most of the year, pond-stocked ﬁsh are subjected to predation and cannot be
efﬁciently treated for prevention and control of diseases (Piper et al. 1982).

Intensive ﬂow-through aquaculture has been used to avoid some of the
problems associated with pond culture of yellow perch (NCRAC 1993). Studies
have shown a constant source of water approximately 22°C (72°F) was needed
for optimum perch growth (Huh et al 1976; Carlander1997). Ground water
temperatures in the NCR have been reported to range from 38°C (38.8°F) to
167°C (62.1°F) (Alliant Geothermal 1998), too low to meet optimum growth
requirements of yellow perch (Huh et al 1976; Carlander 1997). Because of less
than optimal ground water temperatures, water sources used for ﬂow-through
aquaculture in the NCR needs to be heated. Heating large volumes of constantly
ﬂowing water through a single-use raceway is not cost-effective. An economical
method for heating large amounts of ﬂowing water is needed.

Alternative sources for heating water have been used for ﬂow-through
aquaculture. Power plant condenser cooling water from Consumers Energy in
West Olive, Michigan was used as a source of heated water in combination with

controlled lighting to supply optimum growing conditions for yellow perch in a

11

ﬂow-through system (C. Starr, Bay Port Aquaculture, personal communication).
Studies show that few power plants are available to aquaculturists interested in
using heated water from condenser cooling towers (Amundsen and Keenan
1990)

Problems associated with using this source of water developed in
November 2000 when Consumer's Energy incorrectly applied a chlorine
treatment to sanitize their cooling systems. Bay Port Aquaculture lost 100% of
their yellow perch, including broodstock they had been selecting for improved
performance characteristics, in their ﬂow-through system (C. Starr, Bay Port
Aquaculture, personal communication). Production was completely shut down
and the future of Bay Port Aquaculture has been in doubt because of the loss of
their production and broodstock ﬁsh (C. Starr, Bay Port Aquaculture, personal
communication).

RAS technologies have been developed to provide year round optimum
growing conditions for cultured ﬁsh. Typical systems have included aeration,
sedimentation, mechanical ﬁltration, biological ﬁltration, pH control, and water
sterilization (Timmons 2000a; Timmons 2000b). RAS has been designed as a
semi-contained system; make-up water is only needed to replace water lost from
evaporation and to lower concentrations of nitrates, which have been reported
toxic to ﬁsh only at high concentrations (Wickins 1980). Aquaculturists have
used RAS year round to control growing conditions, thus shortening the amount
of time needed for their product to reach market. Yellow perch ﬁngerlings of 15 g

(0.5 oz) have been grown to a market size of 150 g (5.3 oz) in 9 — 11 months

12

using small-scale RAS, feeding pellets, and using rearing conditions of 21°C
(70°F) with a photoperiod of 16:8 hours light to dark (Calbert and Huh 1976).
RAS technology needs to be further developed to allow aquaculturists to produce
an economically viable product while avoiding problems associated with pond
and ﬂow-through aquaculture.

Initial capital investments for RAS have been high because of the
considerable costs associated with system design and construction (Muir 1981 ).
Studies have shown that small-scale RAS models were not proﬁtable (Kocurek
1979; Lipscomb 1995), while historically, large-scale RAS has not been
economically feasible for yellow perch producers (Heidinger and Kayes 1986).
Several perch aquaculturists using large-scale RAS have recently gone out of
business. High start-up costs, system operation costs, low labor efﬁciency,
competition from foreign markets, high cost of available ﬁngerlings, and
inefﬁcient farm operation have all been reasons why commercial RAS
aquaculturists have gone out of business (Malison 1999; Kelly 2000; Timmons
2000c). Thus, economically feasible techniques using large-scale RAS need to

be developed for perch aquaculture.

Gender related growth differences

Studies performed by Huh (1975), Schott (1980), and Malison et al. (1985)
indicated the growth rate of yellow perch signiﬁcantly decreases when the ﬁsh
reach approximately 150 mm (5.9 in), just before they reach a marketable size of

115 g (0.25 lbs) or 200 mm (7.9 in). The reduction in growth rate has lengthened

13

the grow-out cycle and increased the time required for the product to reach
market size.

Male yellow perch have exhibited a greater growth rate reduction than
female perch. Scott and Crossman (1973), Schott (1980), and Malison et al.
(1986) observed that females grow faster and attain larger sizes than male
yellow perch after they reach a size of 110 mm (4.3 in). The gender-related
growth differences have been shown to occur at the onset of sexual maturation
and gonadal development, generally during the ﬁrst year of life (Malison et al.
1986)

Studies have shown that perch fed diets supplemented with estradiol-17B,
an estrogenic compound, exhibited increased growth rates (Malison et al. 1986;
Malison et al. 1988). Malison et al. (1988) reported that the increased growth
rate was a result of increased food consumption, not an increase in food
conversion efﬁciency (weight gain of ﬁsh/weight of food consumed). Increased
food consumption occurred in both genders of yellow perch (Malison et al. 1988).
However, gender-related differences in growth rate remained (Malison et al.
1988). Females outgrew males because they exhibited greater food
consumption rates and higher food conversion efﬁciency (Malison et al. 1988).
Males isolated from females have not exhibited higher growth rates; thus
intersexual competition for food has not occurred (Malison et al. 1988; Amberg
2001). A method to increase male perch growth rate to equal female growth rate

has not been found.

14

Obtaining a 100% female stock for grow-out to avoid gender related
growth differences has been highly desirable to yellow perch aquaculturists
(Malison and Garcia-Abiado 1996). A method for manually identifying gender of
perch greater than 150 mm (5.9 in) with 70% accuracy has been identiﬁed
(Kayes et al. 1998). The urogenital opening was described as round in male
perch and crescent shaped in female perch. Pressure applied to the abdomen of
males resulted in the urogenital opening forming a V towards the pressure point;
conversely pressure applied to the abdomen of females resulted in the urogenital
opening retaining its crescent shape. Separating perch of this size would not be
useful to aquaculturists because 150 mm (5.9 in) individuals are near market size
and a substantial investment of time and money has already been invested to
reach this size. The accuracy of this method decreased to nearly 50% when
applied to perch ﬁngerlings less than 120 mm (4.7 in). Identifying morphological
characteristics, which differentiate gender in small yellow perch ﬁngerlings, would
be desirable so aquaculturists could select females before stocking their grow-
out production system. Amberg (2001) reported morphological differences used
to identify gender of other ﬁshes could not be used to identify the gender of
yellow perch ﬁngertings 130 mm (5.1 in) total length. Amberg (2001) compared
the following morphological characteristics of male and female perch to see if
there were gender related differences: eye diameter, mouth length, mouth width,
mouth height, standard body length and total length, the seminal duct in males,

and urogenital opening manipulations.

15

Feed supplemented with 17a-methyltestosterone, an analog of the sex
steroid testosterone, can be used to create all female stocks of yellow perch
(Malison and Garcia-Abiado 1996). Small ﬁngerlings, 20-35 mm (0.8-1.4 in) in
total length, were fed treated feed until they reached sexual maturity. Treated
females developed a fused ovoteste that was structurally unique from the paired
male testes. XX-sperm was collected from the dissected ovotestes and used to
fertilize eggs from an untreated female ﬁsh. The resulting offspring were 100%
female (Malison and Garcia-Abiado 1996). The described method was recently
approved for an INAD (Investigative New Animal Drug) at the University of
Wisconsin, Madison. If the INAD is approved, commercial aquaculturists could
use 100% female stocks to avoid the problem of slower growing males

decreasing production.

Siggle-size versus multiple-size cohorts

Single-size cohort management has been a commonly used strategy by
commercial aquaculturists (Piper et al. 1982). Under this management strategy,
single-size cohorts have been grown in a production system. Fish were
harvested from single-size cohort systems when they reached market size. The
production system was restocked after all ﬁsh were harvested (Piper et al. 1982).
Studies have shown that channel catﬁsh cultured using single-size cohort
management exhibit less size variation, competition, and difference in feed
conversion efﬁciency (Swindler et al. 1989; Swindler et al. 1990). Some

disadvantages found by channel catﬁsh producers using single-size cohort

16

 

management have been reported: reduced availability of product because ﬁsh
are harvested once per year and cash ﬂow problems associated with an annual
single harvest (Terhune et al. 1997).

Yellow perch culturists typically have not used single-size cohort
management because their farms are usually small with a few culture tanks
(Malison 1999; Kelly 2000). Farms using single-size cohort strategy would not
be optimizing their culture tank volume since culture tanks would be partially
harvested as some ﬁsh reached market size. Growth has been shown to be
highly variable (Scott and Crossman 1973; Schott1980; Malison et al. 1986), so
initial harvests would not remove the entire stock, thus causing the culture tanks
to be only partially stocked. Since perch ﬁngerlings take 1-3 years to reach
market size (depending on culture method), aquaculturists would not be able to
supply fresh ﬁsh to their primary markets on a continuing basis when using
single-size cohort strategies.

Aquaculturists have used multiple size-continuous loading strategies
because it generated more than one harvest from one culture system (Piper et al.
1982; Busch 1985) and increased income throughout the year (Busch 1985).
This method uses multiple-size cohorts where ﬁsh are harvested once they reach
market size. Harvested ﬁsh are replaced with ﬁngerlings in the production
system, thus providing a continuous running culture system. As an example,
channel catﬁsh in multiple-size cohorts have been cultured in one pond. When
the largest cohort reached market size, the ﬁsh were harvested and replaced

with ﬁngerlings (Busch 1985).

17

Yellow perch producers have periodically harvested food-size ﬁsh from
their production system to meet buyer demand. Yellow perch producers
generally market their product directly, without beneﬁt of wholesalers or
processors. One of the primary markets for yellow perch has been the restaurant
trade (Riepe 1997). Restaurant owners have expressed their desire for year-
round availability of a fresh product. Multiple harvests allow aquaculturists to
meet this demand for fresh ﬁsh (Mike Libbin, Paragon Aquaculture, personal
communication).

Problems with multiple size—continuous stocking can occur if faster
growing ﬁsh are harvested at higher rate than slower growing ﬁsh. Since yellow
perch females have been shown to grow faster than males, initial harvests would
be predominately female (Scott and Crossman 1973; Schott 1980; Malison et al.
1986). Replacement ﬁngerting cohorts could consist of a nearly equal gender
distribution. Eventually slower growing males may predominate in the production
system population, causing a reduction in harvest rate. Channel catﬁsh
producers using multiple batch management have been able to harvest ﬁsh
throughout the year; but, variation in ﬁsh size occurred because of competition
between large and small ﬁsh (Collier and Schwedler 1990) and differences in
food conversion efﬁciency (Busch 1985).

Cultured ﬁshes in multiple-size cohorts may form feeding hierarchies.
Studies have shown larger ﬁsh become more aggressive and dominant affecting
the appetite and/or feeding of subordinate ﬁsh in a culture system (Silva and

Anderson 1995). Salmonids have been shown to develop dominance and size

18

hierarchies when cultured at low densities and feed was introduced in one
location of the production system (Thorpe et al. 1990; Ryer and Olla 1991 ).
Studies of Paciﬁc salmon reared in cages where feed was introduced at the
same location have shown that 25% of the ﬁsh consumed most of the feed (Olla
et al. 1990).

Feed management in multiple size-continuous loading cohorts is difﬁcult.
As ﬁsh reared in single-size cohorts grew, feed sizes were increased to enhance
feed utilization (Ramseyer and Garling 1997). Since ﬁsh in multiple-size cohorts
vary in size, some ﬁsh consumed pellets that were not optimal size. Hardy
(1989) observed that pellets too large to consume broke down and leached
nutrients into the system before they degraded to a size ﬁsh could eat. Feeding
a pellet smaller than optimal has been shown to promote feed waste and
increase nutrient leaching because of increased surface to volume ratio in
smaller pellets (Hardy 1989). Pigott and Tucker (1989) indicated that smaller
feeds, such as crumble diets, were more irregularly shaped than larger round
feeds, thus having a greater surface area which has caused an increase in
nutrient leaching. Despite problems with either method, feeding pellets smaller
than optimal has been preferred to larger than optimal when feeding ﬁsh (Leitritz
1959).

Commercially formulated diets speciﬁc to yellow perch have not been
developed. C. Starr (Bay Port Aquaculture, personal communication) indicated
that perch grow well when fed a commercial rainbow trout diet. Optimum pellet

size for yellow perch has been shown to be similar to optimum pellet size for

19

similar sized rainbow trout (C. Starr, Bay Port Aquaculture, personal
communication). Cho (1990) determined the optimum pellet size for rainbow
trout to be 0.5 — 1.5 mm (0.02 — 0.06 in) granules for 1 — 10 g (0.04 - 0.35 oz)
ﬁsh, 2 - 3 mm (0.08 — 0.12 in) granules for 20 — 40 g (0.71 — 1.41 oz) ﬁsh, 3 — 4
mm (0.12 — 0.16 in) granules for 50 — 100 g (1.76 - 3.53 02) ﬁsh, and 5 —- 7 mm
(0.20 — 0.28 in) granules for ﬁsh over 200 g (7.06 oz).

A combination of multiple- and single-size cohort management could be
useful to yellow perch aquaculturists. Production systems with cages that isolate
single-size cohorts within a single pond have been developed for channel catﬁsh
(Schwedler et al. 1990; Terhune et al. 1992; 1997). These systems allow for
multiple harvests per year while maintaining the beneﬁts of single-size cohort
management. Fish are graded on a regular basis to maintain single-size cohorts.
Channel catﬁsh size-graded before stocking exhibited reduced size variation
when harvested from ponds (Huner et al. 1984) and tanks (Carmichael 1994).
Rainbow trout and salmon producers have commonly graded their ﬁsh into
single-size cohorts (Leitritz 1959). The beneﬁts of this practice have been shown
to be: enhancing growth, reducing cannibalism, maintaining an accurate
inventory, and facilitating calculation of the amount, frequency, and size of feed
needed for ﬁsh in a single-size cohort (Leitritz 1959).

Yellow perch aquaculturists could utilize a combination of multiple— and
single-size cohort management. Studies have shown that perch do not grow as
well when conﬁned in ponds using net pens as they do in unconﬁned ponds

(NCRAC 1992). However, RAS systems could be designed to segregate cohorts

20

by using a multiple number of smaller tanks per bioﬁlter instead of fewer larger
tanks. Flow through systems could be designed to segregate cohorts through
the use of multiple raceways or screens dividing raceways. Any of these
methods may allow perch producers to have multiple harvests per growing

season .

21

MATERIALS AND METHODS

This research project was designed to evaluate growth and performance
of yellow perch in experimental and commercial settings using continuous
loading-multiple size cohort management and single-size cohort management
strategies. Bay Port Aquaculture Systems, Inc. (West Olive, MI) was to conduct I:
single-size cohort management with yellow perch in a RAS on a commercial
scale and Paragon Aquaculture (Oshkosh, WI) was to conduct continuous

loading-multiple cohort management with yellow perch in a RAS on a commercial

 

scale.

MSU researchers were to assist Paragon Aquaculture and Bay Port
Aquaculture Systems, Inc. with planning and conducting the commercial-scale
experiments by assisting in marking ﬁsh, data collection, and statistical analysis.
MSU researchers were to travel to both commercial operations prior to initiation
of experiments and at six month intervals afterward. The commercial-scale

results were to be compared to the small-scale experimental results.

MSU Culture Facilities and RAS

Yellow perch were obtained from Bay Port Aquaculture and transported to
the Michigan State University Aquaculture Lab in a 681-L (180.gal) transport
tank. The transport tank was equipped with aeration and ﬁlled with 11°C (52°F)

well water from Bay Port Aquaculture. Fish were held in a 1893-L (500-gal) tank

22

with a center bottom drain for acclimation to MSU lab conditions. The holding
tank was supplied with 105°C (51°F) well water at a rate of 10 me (2.6 gpm).
The experiment was conducted using RAS. Nine, 190-L (50-gal) oval
ﬁberglass Model OT Frigid Units, Toledo, Ohio, culture tanks were used. Well
water was pumped into each research tank through a valve positioned above one
end of each tank. Water ﬂowed through the tank and out the bottom of the
opposite end. External standpipes were used to promote more efﬁcient solids
removal from the bottom of the tanks (Figure 1). Water ﬂowed down a rain gutter
and into a 606-L (160-gal) rectangular solids removal tank. A screen of fumace-
ﬁlter material removed large solid material as the water passed into the solids
removal tank. Water passed through another fumace-ﬁlter screen inside the tank
to remove smaller material. The screens were removed and cleaned once a
week. A standpipe was set at the end of the solids removal tank so water was
removed from the top of the tank to prevent settled solids from passing in to the
bioﬁlter tank. Two bioﬁltration methods were used in an 1135—L (300-gal) tank; a
40 m2 (431 ft2) rotating biological contact ﬁlter and a bio-bag ﬁlled with
approximately 23 m2 (248 ftz) shredded plastic. Nitrifying bacteria colonized the
bioﬁlter prior to the initiation of the experiment by adding ammonia to the culture
system three months prior. The nitrifying bacteria were already present in the
water used in the culture system, the added ammonia caused the bacteria to
multiply to levels high enough to conduct the experiment. Nitrifying bacteria
converted ammonia to nitrite and then to nitrate. The bioﬁltration tank was

aerated using three air diffuser stones to provide dissolved oxygen (D0) to the

23

Figure 1. Conceptual ﬂow diagram of the RAS used in experiment with close-up
of culture tank design.

TOP VIEW

solids removal tank

 

 

bi oﬁltrati on tank ﬁltration and settling ‘

 

   

 

 

 
   
   
 

 

 

rotating biological
contact ﬁlter and %
bio-bag £9
9
a
3 3
CI -—> 3; 3,
pump 3
(I)
a:
'E
Q)
(I)

 

 

 

 

SIDE VIEW OF INDIVIDUAL CULTURE TANK

valve external standpipe

K water inﬂow ﬂows into gutter

E /
‘ culture tank >

L1—

water outﬂow j

waW’
I

 

 

 

 

 

 

 

 

 

 

 

 

 

\valve

24

nitrifying bacteria. Water was pumped from the bioﬁlter to the experimental
culture tanks.

Well water was used to ﬁll the RAS and to replace water lost to
evaporation, and water lost during cleaning and weigh-out procedures.
Replacement water was added at a rate of approximately 10% per day. Water ,
temperature was maintained by ambient room temperature at 20 at 2°C (68 3:
36°F). A photoperiod of 16 hours light to 8 hours dark was maintained using
ambient lighting supplemented with four overhead Philips 34 watt
phosphorescent lights. The water exchange rate in the culture tanks was
maintained at 3.15 me (0.83 gpm) to allow for complete water exchange every
hour. Aeration was supplied to each culture tank to maintain DO levels at a
minimum of 4.0 ppm (Glass 1991). Total ammonia and pH were monitored
biweekly and maintained below 0.4 ppm total ammonia and between 7.8 to 8.3
pH using water replacement. These levels have been shown to be safe for

yellow perch (Glass 1991).

Experimental desm

A replicated comparison of growth and performance of yellow perch grown
under single cohort or continuous loading-multiple size cohort management was
designed to last until large single-size cohort ﬁsh attained market size or nine
months, whichever occurred ﬁrst. Two size cohort categories were deﬁned:

small, 9.4 i 0.7 cm (3.7 i 0.3 in) and large, 11.5 i 0.8 cm (4.5 i 0.3 in). Tanks

were randomly assigned a single-size small group, a single-size large group, or a

25

mixed-size group of equal numbers of small- and large-size ﬁsh. A right pelvic ﬁn
clip identiﬁed small-size ﬁsh in the mixed-size groups.

Triplicate groups of 20 yellow perch ﬁngerlings were randomly stocked as
single-sized or mixed-sized cohorts. The stocking density of 20 ﬁsh per tank was
calculated by using half the recommended maximum density allowed by total
bioﬁltration surface area to allow for partial cleaning of ﬁltration media and
replacement of bacteria colonies (D. Garling, Michigan State University, personal
communication). An even sex distribution throughout single and mixed cohorts
was assumed. Tanks were stocked using the following method:

1. Tanks were assigned single-size or mixed-size groups by using a random
numbers table.

2. A single small-size ﬁsh was placed in an appropriately assigned tank.
Fish placed in a mixed-size group were given a right pelvic ﬁn clip before
stocking. One ﬁsh was placed in each tank before a second ﬁsh was
stocked. The mixed-size group tanks received 10 ﬁsh; the single-size
group tanks received 20 ﬁsh.

3. A single large-size ﬁsh was placed in an appropriately assigned tank.
One ﬁsh was placed in each tank before a second ﬁsh was stocked.
The mixed-size group tanks received 10 ﬁsh; the single-size group tanks
received 20 ﬁsh.

Market—size ﬁsh of 115 g (0.25 lbs) (approximately 20 cm or 7.9 in total
length) were to be removed from the continuous loading-multiple size cohort

tanks and replaced by 5 - 7.5 cm (2 - 3 in) total length ﬁsh.

26

Fish were fed a commercial trout diet, Purina AquaMax Grower 400 (lot A-
5004), containing at least 45% crude protein and at least 16% crude lipids. Feed
was fed at a rate of 2% total body weight per day, split into 3 feedings (08:00,
12:00, 18:00). The feed and feeding rates were set at a rate and frequency
similar to the commercial cooperators (C. Starr, Bay Port Aquaculture, personal
communication). The initial pellet size was 3 mm (0.12 in), optimum size for the
smallest-sized ﬁsh used. Feed was introduced by hand.

Growth was measured as total wet weight per tank every 4 weeks and
feeding amounts were adjusted. Total tank weight was monitored using the
following method:

1. A single tank was drained to 1/4 volume for easier ﬁsh collection.
2. All ﬁsh from one tank were netted and placed in a tared 7.57 L (2 gal)
bucket + water.
3. Total ﬁsh wet weight was recorded to the nearest 0.1 g (0.004 02).
4. Fish were returned to their tank and water volume was returned to original
level.
Total length of large-size ﬁsh in mixed-size cohorts was measured during
weighing to determine if any had reached market size.

Upon completion of the experiment, all ﬁsh were euthanized using MS-222
at a dose rate of 1ppt for at least 10 minutes. Immediately following euthanasia,
ﬁsh were weighed to the nearest 0.019 (0.0004 02) and total length (mm) was
recorded. The presence/absence of a right pelvic ﬁn clip was identiﬁed and

dissection was performed to determine gender. Fish were placed into freezer

27

bags by gender, size cohort and tank, then frozen at a temperature of -20°C (-

4°F) for 24 hours. Frozen ﬁsh samples were homogenized using a hand grinder.

Proximate analysis

Proximate analysis (moisture, ash, crude protein, crude fat, and total gross
energy) was determined using standard AOAC (1990) methods. One gram (0.04
oz) subsamples per homogenate sample were analyzed in triplicate. Moisture
content was determined by using a Fisher Scientiﬁc |sotemp® Oven Model 655F
(MSU Fisheries Research Lab) at a temperature of 104 i 1°C (219 i 1.8°F) for
48 hours. Ash content was determined by using a Hotpack Model # 770770
mufﬂe furnace (USGS, Ann Arbor) at a temperature of 600°C (1112°F) for 18
hours. Crude protein content was determined by using a Leco 2000 FP nitrogen
analyzer (Animal Science Department, Michigan State University). Crude fat was
determined by using ether extraction in a Sockslet Apparatus (Animal Science
Department, Michigan State University). Total gross energy was determined by
using a Parr 1241 Bomb Calorimeter (Animal Science Department, Michigan
State University). Final proximate analysis data was determined on a percent dry

matter basis.

Statistical analysis
A linear regression model was used to extrapolate when the large and
small-size cohorts would reach market size by using total tank weight of 2300 g

(5.1 lbs) (mean weight 115 g or 0.25 lbs), assuming growth rate remained

28

constant past the end of the experiment. An analysis of covariance was used to
determine differences between the growth rate of large- and small-sized cohorts
(SYSTAT 9, 1999). A Chi-squared test was used to test for even gender
distribution throughout single and mixed-size cohorts. A 2 x 2 Chi-squared test .
was used to determine if there was a signiﬁcant difference in gender ratio
between single and mixed-size cohorts. A one-way ANOVA and Tukey-Kramer
test (SYSTAT 9, 1999) was used to compare ﬁnal size differences between
single— and mixed-cohorts and gender, and to compare moisture, ash, crude
protein, crude fat and total gross energy content by cohort and gender.
Differences were considered signiﬁcant if P s 0.05. A Bonferroni adjustment for
multiple comparisons was applied to the P value for proximate analysis data
because samples were taken from the same homogenate and multiple
comparisons were made with each sample. The adjusted P value considered to

be signiﬁcant for proximate analysis data was P 5 0.002.

29

RESULTS

The main objective of this study was to compare the growth rate of small-
and large-size yellow perch cohorts cultured in either a continuous loading-
multiple size cohort system or a single-size cohort system. The results from this
experiment were to have been compared to the results of the two commercial-
scale projects funded through NCRAC. Paragon Aquaculture (Oshkosh, WI) was
not able to complete their portion of the project. Paragon purchased ﬁsh from
Bay Port Aquaculture and stocked them into the RAS containing ﬁsh as part of
their continuous loading-multiple cohort management strategy. These ﬁsh were
infected with a disease of unknown origin, causing a near 100% ﬁsh kill in
Paragon’s grow-out system. Paragon ceased business operations in the ﬁrst
year of the project (NCRAC 1999). Bay Port Aquaculture Systems, Inc. (West
Olive, MI) was not able to perform their part of the project due, in part, to a near
100% ﬁsh kill from chlorine toxicity caused by a faulty chlorine treatment by
Consumers Energy, Bay Port’s main source of water. Bay Port Aquaculture
ceased operation of their yellow perch facility in the third year of the project
(NCRAC 2001).

The experiment conducted at MSU was to be the ﬁrst of at least two
experiments comparing continuous loading-multiple size cohort management to
single-size cohort management for yellow perch aquaculture. Subsequent
experiments were to be conducted based on the ﬁndings of the initial experiment

and other yellow perch research conducted by MSU researchers. The initial

30

experiment was delayed three times and started over a year later than planned
because of ﬁsh health problems and ﬁsh availability. MSU researchers decided

only one experiment could be conducted because of these delays.

 

Total tank weight

Total tank weight of 20 ﬁsh per tank was used to determine growth
throughout the experiment to minimize handling stress from weighing individual
ﬁsh. Mean initial total tank weight for the single-sized small cohort tanks was

178.3 i 8.8 g (0.39 i 0.02 lbs). Mean initial total tank weight for the single-sized
large cohort tanks was 317.8 i 6.6 g (0.70 i 0.01 lbs). Mean initial total tank
weight for the mixed-size cohort tanks was 259.3 :l: 4.9 g (0.57 :t 0.01 lbs). Total

tank weight was measured every 4 weeks throughout the 277 day experimental
period (Table 1). Mean ﬁnal tank weight for the single-sized small cohort tanks
was 1227.5 : 16.8 g (2.70 i 0.04 lbs). Mean ﬁnal tank weight for the single-sized
large cohort tanks was 1607.1 : 75.5 g (3.54 i 0.17 lbs). Mean ﬁnal tank weight
for the mixed-size cohort tanks was 1461.1 i 211.0 g (3.21 i 0.46 lbs).

Yellow perch in the mixed-size cohorts did not reach market size by the
end of the experiment, so no ﬁsh were replaced. One pellet size was used
throughout the experiment because the smallest ﬁsh in both the single— and
mixed-size tanks did not grow large enough to consume the next larger-sized
pellet. A pellet diameter of 3-4 mm (0.12 — 0.16 in) was used (Cho 1990).

Linear regression equations were generated to predict when large and

small single-size cohorts would reach a mean market size of 115 g (0.25 lbs) by

31

Table 1. A summary of total tank weight (9) over 9-month experiment. SS =
Single-Size Small Cohort, SL = Single-Size Large Cohort, M = Mixed-Size
Cohort.

tank 4 tank5 tank6
SS SL SL SS SS M

168.7 310.2 . .4 180. 186.0 265.
.5 .
7.

6-Jan .5
eb 1 45.5

 

32

using total tank weight. If total tank weight were 2300 g (5.1 lbs), perch would
have been a mean size of 115 g (2300 total 9 of ﬁsh/20 ﬁsh). The generated
equation for the large-size cohort was y = 4.9466x + 262.8, where x = days and y
= total tank weight of 2300 g. The large-size cohort would have taken a total of
412 days to attain market size. The trial would have required an additional 135
days (412 total days - 277 days of the trial) for the large size cohort to reach
2300 g (R2 = 0.9823) assuming continued linear growth (Figure 2). The
generated equation for the small-size cohort was y = 4.0726x + 119.85, where x
= days and y = total tank weight of 2300 g. The small-size cohort would have
taken a total of 535 days to attain market size. The trial would have required an
additional 258 days (535 total days - 277 days of the trial) for the small-size
cohort to reach 2300 g (R2 = 0.9825) assuming continued linear growth (Figure

3). Final mean weight and length data are reported in Table 2.

Gender distribution

 

Sex distribution throughout single— and mixed-size cohorts was 89:91
females to males. Single-size small cohorts contained 27:33 females to males.
Single-size large cohorts contained 32:28 females to males. Mixed-sized cohorts
contained 14:16 small-size females to males and 16:14 large-size females to
males. All cohorts were not signiﬁcantly different from a 50:50 gender
distribution and there were no signiﬁcant differences in gender distribution

between single— and mixed-size cohorts.

33

Figure 2. Growth of large single-size cohort over nine month experiment. Linear
regression equation predicts the cohort would have reached market size 135
days (4.5 months) after completion of grow-out trial assuming continued linear
growth.

1800
1600 3
1400 I

1200 l

 

1000,

  

weight (g)

800 J
y = 4.9466x + 262.8

R2 = 0.9823

 

ﬂ—l

0 30 60 90 120 150 180 210 240 270 300
days

34

Figure 3. Growth of small single-size cohort over nine month experiment. Linear
regression equation predicts the cohort would have reached market size 258

days (8.5 months) after completion of grow-out trial assuming continued linear
growth.

weight (g)

1200

1000 .f

1800 -,

l

1600 .7

y = 4.0726x + 119.85

1400 ., R2 = 0.9825

l

      
 

l

800

600 ,

 

 

400 f.
200
l
0 "T" _-— .T ' T _—‘_—_ T ""—_‘T__ "—_"' "—T___ # —ﬁ
0 50 100 150 200 250 300

days

35

Table 2. Final mean lengths (mm) and weights (9) of yellow perch by gender and
cohort. SS = Single-Size Small Cohort, SL = Single-Size Large Cohort, MS =

Small Fish Within Mixed Size Cohort, ML = Large Fish Within Mixed-Size Cohort.
Corresponding letters indicate no signiﬁcant difference between means, P > 0.05.

_ SS

 

186.78 :t 11.65‘1

186.36 i 14.12El

199.62 i 15.02”

199.69 i 12.54"

 

74.03 :I: 13.88c

75.69 :t 18.31°

90.78 i 1927"

93.83 i 20.65"

 

males mean
length

164.12: 9.189

170.37 :1: 86C?

178.64 i 7.84'

176.23 i 10.66Y

 

males mean

 

48.61 :I: 8.699

 

57.65 1; 11.89'1

36

 

64.33 i 10.15n

 

62.00 :I: 13.26"

 

Final size difference by cohort aniqender

The ﬁnal mean weight of large- and small-size females and males in
single-size cohorts was compared to the ﬁnal mean weight of large- and small-
size females and males in the mixed-size cohorts (Figures 4, 5, 6 and 7). The
only signiﬁcant difference was the ﬁnal mean weight of small males in the single-
size cohort was signiﬁcantly lower than the ﬁnal mean weight of small males in
the mixed-size cohort, P < 0.05 (Figure 7). There was no signiﬁcant difference
between small and large males within mixed-size cohorts, P > 0.05 (Figure 8).
Females were signiﬁcantly larger than males within each size class in single and

mixed-size cohorts, P < 0.05 (Figures 9, 10, 11 and 12).

Proximate analysis

 

Final proximate analysis data for feed and single and mixed-size cohorts
by gender is summarized in Table 3. Comparisons between single and mixed-
size cohorts were made within and between genders. Comparisons were also
made between large and small cohorts and total males and females. All values
were reported as a percent dry weight basis.

Mean percent moisture content for males ranged from 69 to 71% within
single and mixed-size cohorts. Mean percent moisture content for females was
70% within single— and mixed-size cohorts. No signiﬁcant differences in percent
moisture content were observed in comparisons between cohorts or genders.

Mean percent ash content for males and females ranged from 4 to 5%

within single- and mixed-size cohorts. No signiﬁcant differences in percent ash

37

Figure 4. Final mean weight and standard deviation of large-size females within
single- and mixed-size cohorts. Values were not signiﬁcantly different, P > 0.05.

120

 

100 l——

 

 

 

 

I mixed cohort

weight (g)
8

 

to single 00an

 

 

20

 

 

 

 

 

 

38

Figure 5. Final mean weight and standard deviation of small-size females within
single- and mixed-size cohorts. Values were not signiﬁcantly different, P > 0.05.

120

 

 

100 l.-..-._. l. l_ _. ,r_l_l -

 

 

 

a single cohort
I mixed cohort i

 

 

weight (g)

 

 

 

 

 

39

Figure 6. Final mean weight and standard deviation of large-size males within
single- and mixed-size cohorts. Values were not signiﬁcantly different, P > 0.05.

 

120

100 ..._ , v A '._,A-,____ _.

 

; [3 single cohortl
. mixed cohort
L_

weight (g)

 

 

 

 

 

40

Figure 7. Final mean weight and standard deviation of small-size males within
single- and mixed-size cohorts. Small-size males in mixed-size cohorts were
signiﬁcantly larger than small-size males in single-size cohorts, P < 0.05.

 

 

 

 

120

100-_l___,-lll_l_l_r

80 ._ - - l -v +
a ' 0
g gsmglecohort]
-% (.mixedcohort
3

 

 

 

 

 

 

 

 

 

41

Figure 8. Final mean weight and standard deviation of large- and small-size
males within mixed-size cohorts. Values were not signiﬁcantly different, P >
0.05.

120

 

100 L_l_. l_l_w-l_rlll__ll_l.ll,v__,_m

80 +m_mn ll. 2, . __- __l__. ____-

62 00 ”3 large males :

I. small males

 

 

weight (g)
8
l
l
0|
‘1
a:
ct

 

 

40 3.“. .22

20 _____ l

 

 

 

 

 

males

42

Figure 9. Final mean weight and standard deviation of large-size females and
males within single-size cohorts. Females were signiﬁcantly larger than males, P
< 0.05.

120

 

100 _. l #-l_.____. ‘I’_A _

 

80 +— __ .. WM __ﬁ.ﬂ

 

 

 

Cl large females l
"—’T“ |

. large males ‘

 

weight (g)
8
l
l
l

40 -. _._. -2

20 + .2

 

 

 

 

 

gender

43

 

Figure 10. Final mean weight and standard deviation of large-size females and

males within mixed-size cohorts. Females were signiﬁcantly larger than males, P
< 0.05.

120

 

10° -- A—Essas—m—E —~

 

80 l- tr-

 

 

[jlarge females 1
- large males I

__J

 

 

60 t.. ___s

weight (g)

 

40 l _,l“_

20 l_l___

 

 

 

 

 

gender

Figure 11. Final mean weight and standard deviation of small-size females and

males within single-size cohorts. Females were signiﬁcantly larger than males, P
< 0.05.

120

 

100 .9 __ v _..- Al __#-l_.___.r

 

 

 

(3 small females
I small males

 

 

weight (g)
S
l

 

 

20 .___ .—

 

 

 

 

 

gender

45

Figure 12. Final mean weight and standard deviation of small-size females and
males within mixed-size cohorts. Females were signiﬁcantly larger than males, P

< 0.05.

120

 

 

 

IE] small females I
I. small males

 

 

 

 

 

 

weight (g)

 

 

 

 

 

 

gender

46

Table 3. Proximate analysis, on a dry matter basis, for yellow perch fed 2% total
body weight for 9 months. SFS = Small Females Single Cohort, SMS = Small
Males Single Cohort, LFS = Large Females Single Cohort, LMS = Large Males
Single Cohort, LFM = Large Females Mixed Cohort, LMM = Large Males Mixed
Cohort, SFM = Small Females Mixed Cohort, SMM = Small Males Mixed Cohort.
Feed values were signiﬁcantly different from ﬁsh values, all other values are
marked with a x to indicate signiﬁcant difference between means in that column,
P > 0.002.

Protein

H-

1+1+1+1+1+1+1+1+1+1+1+1+1+1+I+
1+ 1+ 1+ 1+ 1+ 1+ 1+ 1+ 1+ 1+ 1+ 1+ 1+ 1+ 1+
1+ 1+ 1+ l+ 1+ 1+ 1+ 1+ 1+ l+ 1+ 1+ 1+ 1+ 1+
1+ 1+ 1+ 1+ 1+ 1+ 1+ 1+ 1+ 1+ 1+ 1+ 1+ H 1+

i
i
i
i
i
i
i
i
i
i'
i
i
i
i'

 

47

content were observed in comparisons between cohorts or genders.

Mean percent crude protein content for males ranged from 59 to 61%
within single- and mixed-size cohorts. Mean percent crude protein content for
females ranged from 58 to 60% within singe- and mixed-size cohorts. No
signiﬁcant differences in percent crude protein content were observed in
comparisons between cohorts or genders.

Mean percent crude fat content for males ranged from 22 to 27% within
single— and mixed-size cohorts. Mean percent crude fat content for females
ranged from 23 to 26% within single- and mixed-size cohorts. A signiﬁcant
difference in percent crude fat content existed between large-size females in
single- and mixed-size cohorts. No other signiﬁcant differences in percent crude
fat content were observed in comparisons between cohorts or gender.

Mean total gross energy (Kcal/g) content for males ranged from 5.43 to
5.62 Kcal/g within single- and mixed-size cohorts. Mean total gross energy
content for females ranged from 5.51 to 5.63 Kcal/g within single- and mixed-size
cohorts. A signiﬁcant difference in total gross energy content was observed
between small-size females and males within single-size cohorts. No other
signiﬁcant differences in total gross energy content were observed in

comparisons between cohorts or gender.

Water quality parameters and mortalities

Water quality parameters were measured biweekly. Total ammonia

ranged from 0.0 to 0.01 ppm, pH ranged from 8.0 to 8.2 and DO ranged from 7.8

48

to 8.4 ppm. Six mortalities occurred throughout the 277 day experiment. Dead
ﬁsh were removed from the culture tank and wet weight in grams was recorded.
The ﬁsh were replaced with a similar size ﬁsh from the original stock of ﬁsh used

at the initiation of the experiment (Table 4).

49

Table 4. Wet weight (g) of mortalities and replacement ﬁsh.

 

 

 

 

 

 

wet weight (g) of wet weight (g) of

mortalities and date replacement ﬁsh
tank 3 14.8 (5/17/00) 15.2
tank 4 16.9 (5/17/00) 16.6
tank 2 33.0 (6/16/00) 32.6
tank 2 16.9 (6/16/00) 16.1
tank 2 23.0 (6/16/00) 22.9
tank 1 46.8 (1/31/01) 47.2

 

 

50

DISCUSSION

Objective 1

The main objective of this study was to compare continuous loading-
multiple size cohort management to single-size cohort management for yellow
perch aquaculture. Prior to this experiment, research had not compared these
two management strategies for yellow perch culture. The ﬁrst null hypothesis
predicted mixed-size cohorts would grow at the same rate as single-size cohorts.
This was true for both genders in the large-size cohorts and for females in the
small-size cohorts. However, the males in the small mixed-size cohort were
larger than the males in the small single-size cohort, thus the null hypothesis for
this case was rejected. Mixed-size cohorts were expected to grow slower than
single-size cohorts due to competition between large and small ﬁsh (Collier and
Schwedler 1990) and differences in food conversion efﬁciency (Busch 1985) that
have been observed in channel catﬁsh production when using mixed-size cohort
management strategies.

The small-size males in mixed-size cohorts grew faster than all other
males in the experiment and were not signiﬁcantly different in size than large-size
males at the end of the experiment. The small-size males in the mixed-size
cohort may have been more aggressive than their counterparts in the single-size
cohort. Research has indicated that male yellow perch of uniform size were not
aggressive feeders (Amberg 2001). The presence of large-size males could

have caused the small-size males in the mixed-size cohort to become more

51

competitive feeders. Studies have shown small-size elvers (Anguilla anguilla)
grew at faster rates than large-size elvers in mixed-size cohorts (Wickins 1987).
Small-size elvers were the same size or larger than 36% of the large-size elvers
after 82 days in mixed-size cohorts (Wickins 1987). The expression of growth in
elvers was not governed by hierarchical position; some other behavioral or
physiological mechanism(s) controlled growth expression (Wickins 1987).

A possible explanation for the male perch in small mixed-size cohorts
being larger than their counterparts in the single-size cohort could have been a
difference in crude fat or protein. However, the proximate analysis data indicated
that the body composition of the small mixed-size males was not signiﬁcantly

different from all the other males.

Objective 2

 

Female perch grew faster than males so the second null hypothesis,
which predicted that male and female yellow perch would grow at the same rate,
was rejected. The results of this experiment were similar to previous
observations by Scott and Crossman (1973), Schott (1980) and Malison et al.
(1986). Amberg (2001) observed that the optimal feeding level for yellow perch
was 1% of total body weight. Perch fed at this ration level did not exhibit as great
of a difference in gender-related growth differences. However, females fed a 1%
ration level grew slower than females fed a higher ration level. Decreasing the

growth rate of perch females would increase the amount of time needed for ﬁsh

52

to reach market size and would not be a management strategy readily accepted
by aquaculturists.

If all-female stocks of yellow perch become readily available at affordable
prices, they may become more desirable than mixed-gender stocks to
commercial producers (Malison and Garcia-Abiado 1996) using continuous
loading-multiple cohort management strategies. This research indicated female
perch in mixed-size cohorts grew at the same rate as females in single-size
cohorts. Since females grew at the same rate using both management
strategies, than there should be no drop-off in production for culturists using the
continuous loading-multiple harvest strategy. However, the results of this
research are only preliminary ﬁndings because the continuous loading
component was not conducted since the large-size ﬁsh did not attain market size
by the end of the experiment. Long-term growth performance of female perch in

a continuous loading-multiple harvest cohort system still needs to be evaluated.

Initial tank wekght

 

Mean initial total tank weight was lower than desired because the large-
size cohort ﬁsh were smaller than originally proposed, 11.5 i 0.8 cm (4.5 i 0.3
in) as opposed to 16.2 i 1.2 cm (6.0 :t 0.5 in). Larger yellow perch were not
available at the initiation of the experiment so smaller ﬁsh were used. The large-
size ﬁsh in the single- and mixed-size cohorts most likely did not reach market
size during the nine month experiment because of their initial size. Feed pellet

size was not changed since some ﬁsh in the large single-size cohort did not

53

attain a large enough mouth gape to consume larger-sized pellets. Larger pellet
sizes could have been fed to the large single-size cohort if the initial stocking size

had been larger.

Mession analysis

Using linear regression equations, the large single-size cohort and small
single-size cohort perch were projected to reach market size approximately 135
and 258 days after the completion of this trial, respectively. The estimated
number of days to market size was based upon the assumption that the perch
would have continued to grow at the same rate, which may not be a valid
assumption. Many researchers have noted that perch growth slows signiﬁcantly
after they reach 150 mm in total length (Huh 1975; Schott 1980; Malison et al.
1985). Large-size ﬁsh in the single- and mixed-size cohorts were not signiﬁcantly
different, so the assumption was made that large-size ﬁsh in mixed-size cohorts
would reach market size at the same time as ﬁsh in the large single-size cohort.

The small mixed-size cohort was not projected to reach market size at the
same time as the small single-size cohort because males in the mixed-size
cohort grew faster than males in the single-size cohort. Assuming growth rates
remained consistent, the small mixed-size cohort would have attained market
size before the small single-size cohort. A projected date was not determined
because small-size ﬁsh in the mixed-size cohort were not measured separately
from large-size ﬁsh. The individual ﬁsh size cohorts would have had to be

identiﬁed and separated at each weigh out causing increased handling stress.

54

A linear regression equation was also used to predict when the large-size
cohorts would have reached market size had the target size of 16.2 i 1.2 cm (6.0
i 0.5 in) or approximately 65 g (0.14 lbs) been available. The large single-size
cohort was predicted to reach a mean tank weight of 1300 g (2.86 lbs) (65 g/ﬁsh
x 20 ﬁsh) 210 days into the 277-day experiment. The large-size ﬁsh in the singe—
and mixed-size cohorts were predicted to reach market size 202 days into the
experiment (277 — 210 + 135) if the initial size had been stocked at the original
desired size and the growth rates continued at the same linear rate.

Finally, the slopes of the two regression equations indicated that the large
single-size cohort grew at a signiﬁcantly faster rate than the small single-size
cohort, 4.95 to 4.07 glday, respectively. Despite the fact there was no signiﬁcant
difference in gender distribution between the large- and small-size cohorts, the
large single-size cohort was 53% female and the small single-size cohort was
45% female which may explain the observed signiﬁcant difference in the

regression slopes.

Proximate analysis

Results of proximate analysis from this experiment were similar to
previously published results for yellow perch. Reinitz and Austin (1980) reported
whole body proximate analysis data for yellow perch fed four different potential
yellow perch diets. Reinitz and Austin (1980) reported values for crude protein,
crude fat, ash and moisture levels of 66.7, 16.5, 15.3 and 73.9% respectively

when fed a diet containing 53.1% crude protein, 15.4% crude fat, 8.6% ash and

55

7.4% moisture. All ﬁsh used in the mixed versus single-size cohort trial
contained crude protein, crude fat, ash and moisture levels of 59.5, 24.5, 4.5, and
70.2% respectively when fed a diet containing 47.9% crude protein, 17.9% crude
fat, 10.3% ash and 7.5% moisture. Amberg (2001) reported similar proximate
analysis values for yellow perch fed the same feed (PURINA AquaMax Grower
400) in a saturation kinetics model used to determine optimal feeding rate.
Amberg (2001) reported values of 60.7% cmde protein, 23.7% crude fat, 9.7%
ash and 68.1% moisture. Amberg (2001) also reported total gross energy levels
of 4.91 KcaI/g compared to 5.56 Kcal/g for perch used in the single versus
mixed-size cohort trial.

The difference between the ash content values reported for the single
versus mixed-size cohort trial and the values reported by Reinitz and Austin
(1980) and Amberg (2001) may have been caused by differences in
methodology. Amberg (Michigan State University, Master’s degree candidate,
personal communication) reported that after ashing samples of homogenized
yellow perch at 550°C, pieces of bone and scale were still intact. Bob Burnett
(Michigan State University, Department of Animal Science Laboratory Manager,
personal communication) indicated samples with intact bone should be ashed at

600°C to assure all organic matter is completely burnt away. Differences

between the crude protein and crude fat values reported by Reinitz and Austin
(1980) and values reported from trials completed at MSU may have resulted from
differences in crude protein and crude fat levels in the diets. Tidwell et al. (1999)

compared temperature to growth, survival, and whole body composition of yellow

56

perch fed a salmonid diet (45% crude protein and 16% crude fat) similar to the
one used in MSU’s aquaculture facility. Reported proximate analysis values for
crude protein, crude fat and ash content were 59.7, 27.5 and 11.1%,
respectively.

Differences in feeding rates, yellow perch stocks, rearing conditions,
experimental duration, and ﬁsh size could account for discrepancies between
previously reported proximate analysis data and data reported here.

Observed signiﬁcant differences in proximate analysis values for the
single versus mixed-size cohort experiment were not consistent. Large-size
females in mixed-size cohorts had a signiﬁcantly higher crude fat level than
large-size females in single-size cohorts, however there were no corresponding
signiﬁcant differences in crude protein or total gross energy content. Small-size
females in the single-size cohort had a signiﬁcantly higher total gross energy
content than small-size males in the mixed-size cohort, but no corresponding
signiﬁcant differences in crude protein or crude fat level. Amberg (2001) reported
no gender related signiﬁcant differences in whole body proximate analysis data
between yellow perch fed a 2% ration.

A possible explanation for the observed signiﬁcant differences may be the
homogenizing process. The ﬁsh were ground using a hand grinder. The grinder
did not produce a consistent whole ﬁsh paste. Large pieces of skin and scale
were left intact through hand grinder inefﬁciency. A blender was used to further
homogenize the whole ﬁsh samples, but it was not sufﬁciently powerful to

homogenize all skin and scale. Some sample loss might have caused the

57

observed signiﬁcant differences in proximate analysis values. lnaccuracy in

measuring techniques could also have been a cause for the observed signiﬁcant

differences.

Objective 3

 

Future research should be conducted to isolate the mechanism(s) causing
the increased growth of small-size male yellow perch in mixed-size cohorts.
Testosterone levels could be measured in both mixed- and single-size cohort
males to determine if small-size males in the mixed-size cohort had signiﬁcantly
higher levels than males in single-size cohorts. Measurements of testosterone
levels needed to be taken from the blood senirn (Dr. Sandy Scott, The Center for
Environment, Fisheries and Aquaculture Sciences United Kingdom, personal
communication). The ﬁsh used in this research were homogenized upon
completion of the experiment. Total body hormone content of the perch used in
the experiment could have been measured, however chances of identifying a
signiﬁcant difference would have been slight because their levels would have
been diluted during the homogenizing process (Dr. Sandy Scott, The Center for
Environment, Fisheries and Aquaculture Sciences United Kingdom, personal
communication). If there had been signiﬁcant differences in testosterone levels
between the small-size ﬁsh in the single- and mixed-size cohorts, than
testosterone concentration differences would have been most obvious in the
blood serum (Dr. Sandy Scott, The Center for Environment, Fisheries and

Aquaculture Sciences United Kingdom, personal communication).

58

The cause of the increased growth of small-size males in mixed cohorts
needs to be isolated. The mechanism(s) possibly could be used to increase
competitiveness of all sizes of male yellow perch.

Small-size males reared in a continuous loading-multiple size cohort may
have grown faster than small-size males reared in a single-size cohort, but the
growth rate was still slower than small-size females.

Commercial aquaculturists using continuous loading-multiple size cohort
management for yellow perch may develop gender-related problems in their
culture system. Since females grow faster, the ﬁrst market size ﬁsh harvested
from the system would have a high female to male ratio. The harvested ﬁsh
would be replaced with smaller ﬁsh presumably exhibiting a 50:50 gender
distribution. There would be an uneven gender distribution in the grow-out
system because the unharvested ﬁsh would exhibit a higher male to female ratio
after the ﬁrst harvest. As this process continues, slower growing males could
come to dominate the grow-out system and cause a decrease in harvest of
marketable size perch.

A shift in gender distribution, to predominantly males, was not observed in
the mixed-size cohorts in the MSU experiment because ﬁsh were not replaced.
The small and large-size females in the single— and mixed-size cohorts were
larger than the large-size males in the single- and mixed-size cohorts (Table 2).
Assuming the growth rates would have remained constant in the mixed-size
cohort, if the experiment had continued, large- and small-size females would

have been harvested before large-size males. Presumably the harvested ﬁsh

59

would have been replaced with perch that were not signiﬁcantly different from an
even gender distribution. An uneven gender distribution would have likely been
observed after the ﬁrst harvest. The predominant male rearing population would
have slowed down production in the mixed-size cohort.

Research needs to focus on ways to increase male yellow perch growth
rates or economical ways to obtain an all-female stock. Commercial perch
producers need to use multiple harvests to provide fresh ﬁsh to their primary
market throughout the year (Mike Libbin, Paragon Aquaculture, personal
communication). Faster growing males should be selected when developing
brood stock. Faster growing male offspring should be used during spawning to
further select for faster growing male brood stock. If the mechanism(s) causing
faster growth in small-size males in mixed-size cohorts could be combined with
selective breeding for faster growing males, problems associated with slower

growing male yellow perch could be eliminated.

60

SUMMARY AND CONCLUSIONS

Average annual temperatures in the NCR are lower than the optimal
temperature for growth of yellow perch (Huh et al 1976; Carlander 1997; NWS
2001), which makes proﬁtable pond culture less feasible. Commercial pond
producers currently operating in the NCR have not reported proﬁtable enterprises
(Malison 1999).

RAS technologies have provided year-round optimum grow-out
temperatures for yellow perch aquaculturists operating in the NCR, however
commercial operators utilizing RAS have not been successful and many have
gone out of business (Malison 1999). During the three years required to
complete the mixed versus single-size cohort trial at Michigan State University,
many commercial producers of yellow perch went out of business. RAS
aquaculture needs further development to reduce costs of production if it is going
to be a successful business venture in the NCR.

The results of this study, by objective, indicate that:

Objective 1: Large- and small-size female yellow perch reared in mixed-
size cohorts grow at the same rate as large- and small-size
females reared in single-size cohorts.

Objective 1: Large-size male yellow perch reared in mixed-size cohorts
grow at the same rate as large-size males reared in single-

size cohorts.

61

Objective 1: Small-size male yellow perch reared in mixed-size cohorts
grow at a signiﬁcantly higher rate than small-size males in
single-size cohorts and grow at a signiﬁcantly higher rate than
Large-size males in single— and mixed-size cohorts.

Objective 2: Large- and small-size female yellow perch reared in single-
and mixed-size cohorts grow at a signiﬁcantly higher rate
than large- and small-size males reared in single- and mixed-

size cohorts.

 

Objective 3: Continuing research needs to be performed to determine the r
mechanism(s) causing small-size male perch in mixed-size
cohorts to grow at a higher rate than their counterparts in
single-size cohorts. Blood hormonal content should be
measured to determine if the small-size males in mixed-size
cohorts have signiﬁcantly higher levels of testosterone than
other males in the experiment.

This research further demonstrated that female yellow perch grow at a
faster rate than male perch. This research also demonstrated that females
reared in mixed-size cohorts grew at the same rate as females reared in single-
size cohorts. These preliminary results indicate that yellow perch aquaculturists
using RAS may be able to use continuous loading-multiple size cohort
management strategies using an all-female stock of ﬁsh. However, if a mixed-
gender stock is used, over time slower growing males may predominate the

biomass. lf mechanism(s) causing faster growth rate of small-size male perch in

62

 

mixed-size cohorts can be identiﬁed and used to increase the growth rate of all
male perch, culturists could use continuous loading-multiple size cohort
management strategies without obtaining an all-female stock. Methods for
selecting faster growing male yellow perch or Federal approval for the use of
testosterone to create all-female stocks need to be developed to overcome the
gender-related growth differences observed in yellow perch aquaculture.
Research is needed to enhance the proﬁtability of commercial yellow
perch aquaculture in the NCR. Improvements in larval rearing techniques,
recirculating technologies, stocking strategies, and brood stock development are

some of the areas that need further development.

63

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