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This is to certify that the

thesis entitled

Effect of Gender on Nutritional Requirements
of Nile Tilapia Oreochromis niloticus

presented by

Ibrahim Al—Mohsen

 

 

 

has been accepted towards fulfillment
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1/98 animus-p.14

 

EFFECT OF GENDER ON NUTRITIONAL REQUIREMENTS
OF NILE TILAPIA OREOCHROMIS NILOTICUS
By
Ibrahim Al-Mohsen

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
1 998

ABSTRACT

EFFECT OF GENDER ON NUTRITIONAL REQUIREMENTS
OF NILE TILAPIA OREOCHROMIS NILOTICUS

By

Ibrahim Al-Mohsen

Nile tilapia (O. niloticus) males grow faster than females in mixed gender
groups under intensive aquaculture because of their eady maturation and
frequent breeding. This study was designed to determine if the saturation kinetic
model could be used to describe weight gain and net nutrient deposition as a
function of nutrient intake. Nutrient response curves were developed for female,
male, and mixed gender groups fed varying levels of a commercial diet for six
weeks. The shape of the curve (n), curve parameters (Rm, Kw b), and
calculated maintenance level (ML) varied between gender groups. All-male Nile
tilapia gender groups grew faster than female otmixed-gender groups. Males
exhibited higher Rm and K0,, for growth than female or mixedgender groups
because they used fat, protein and energy more efficiently. Based on our
results, methods to provide all-male tilapia for aquaculture should be used to

maximize growth and performance.

DEDICATION

This thesis is dedicated with gratitude to my father and mother and my wife
Maha without whose encouragement, patience and prayers, this work could
never have been completed; I shall be grateful to them to the rest of my life.

Dedicated also to brothers, sisters, and other relatives.

iii

ACKNOWLEDGMENTS

My most and foremost gratitude and praise go to Allah (God) who
provided me with patience and strength to complete this work. I deeply thank my
wife Maha for her enduring patience, abundant prayers, and unceasing
encouragement during my ups and downs throughout my studies.

Special thanks, respect, and appreciation go to Dr. Donald Garling Jr., my
major professor, for his generous assistance and valuable time, encouragement
he offered me throughout my master program and, particularly, this work. His
prompt response and advice are deeply appreciated. I would like to extend my
sincere thanks to members of my master guidance committee: Dr. Gretchen Hill
and Dr. Ted Batterson for their assistance and advice.

I would like to express my appreciation and thanks to the King Faisal
University, Saudi Arabia, for their financial support.

Special thanks to Dr. L. Preston Mercer (head of the Nutrition department,
University of Kentucky at Lexington) for his assistance and providing the
Saturation Kinetic Model software and to Dr. Ibrahim Belal for his time and
guidance.

Last but not least, warm thanks are extended to my friends: my lab
partner Marty Riche for his time, discussion, and assistance especially during
the experimental work and Ahmed Al-Hajjaj for his assistance in the statistical

analysis part.

iv

TABLE OF CONTENTS

LIST OF TABLES ................................................................................................ vi
LIST OF FIGURES ............................................................................................. viii
INTRODUCTION .................................................................................................. 1
LITERATURE REVIEW ........................................................................................ 6
METHODS AND MATERIALS ............................................................................ 17
Fish .......................................................................................................... 18
Feed and Feeding .................................................................................... 18
Water ....................................................................................................... 19
Proximate Analysis ................................................................................... 19
Statistical Analysis ................................................................................... 20
RESULTS ........................................................................................................... 22
Growth ...................................................................................................... 28
Crude Protein ........................................................................................... 33
Crude Fat ................................................................................................. 38
Total Ash .................................................................................................. 43
Gross Energy ........................................................................................... 48
DISCUSSION ...................................................................................................... 53
Growth ...................................................................................................... 53
Crude Protein ........................................................................................... 58
Crude Fat ................................................................................................. 60
Total Ash .................................................................................................. 61
Gross Energy ........................................................................................... 63
CONCLUSION .................................................................................................... 65
REFERENCES ................................................................................................... 66
APPENDIX TABLES .......................................................................................... 74

Table

LIST OF TABLES

The initial weight, final weight, weight gain and feed fed to female,
male, and mixed gender groups of O. niloticus over a six week
experimental period. Each value represents the mean and
standard deviation for three replicate tanks per feeding rate
percentage ................................................................................... 23

The dietary intake and response analysis for growth, protein, fat,
ash, and gross energy by female, male, and mixed gender groups
of O. niloticus over a six week experimental period. Intake and
responses are in grams for all response variables except gross
energy, which is in Kcal. Each value represents the mean and
standard deviation for three replicate tanks per feeding rate
percentage .................................................................................. 24

The proximate analysis of female, male, and mixed gender groups
of O. niloticus fed varying rates of feed over a six week
experimental period. Each value represents the mean and

standard deviation for three replicate tanks per feeding rate
percentage. All percentages are on a dry matter basis ................. 26

Parameters (Rm, maximum theoretical response; Kors = feed
intake that produced half of the maximum response; n = kinetic
order of the model curve; b = predicted response at % feed intake;
ML = maintenance level) calculated for the theoretical response
curves for growth, protein, fat, ash, and gross energy for female,
male, and mixed gender groups of O. niloticus over a six week
experimental period ....................................................................... 27

Comparison parameters table for growth between the three fish
gender groups of O. niloticus. The degree of freedom = 11. ......... 32

Comparison parameters table for protein between the three fish
gender groups of O. niloticus. The degree of freedom = 11. ......... 37

Comparison parameters table for fat between the three fish gender
groups of O. niloticus. The degree of freedom = 11. ..................... 42

vi

Comparison parameters table for ash between the three fish
gender groups of O. niloticus. The degree of freedom = 11. ......... 47

Comparison parameters table for gross energy between the three
fish gender groups of O. niloticus. The degree of freedom = 11. .. 52

vii

Figure

LIST OF FIGURES

Theoretical nutrient curve of growth weight (g) in the feed intake vs
growth weight (9) response (gain or lose) by the female of Nile
tilapia O. niloticus fish throughout the experiment period (6
Weeks). [The dotted line is the 95% confidence interval, the (A)s
are the real observed group of fish, and the zero (0) line (parallel to
the x-axes) represents the maintenance level]. ............................. 29

Theoretical nutrient curve of growth weight (g) in the feed intake vs
growth weight (9) response (gain or lose) by the male of Nile
tilapia O. niloticus fish throughout the experiment period (6
Weeks). [The dotted line is the 95% confidence interval, the (A)s
are the real observed group of fish, the zero (0) line (parallel to the
x-axes) represents the maintenance level, and the perpendicular
line that join both the zero line and the x-axes represents the
maintenance amount of the treatment for each curve]. ................. 30

Theoretical nutrient curve of growth weight (g) in the feed intake vs
growth weight (9) response (gain or lose) by the mixed gender of
Nile tilapia O. niloticus fish throughout the experiment period (6
Weeks). [The dotted line is the 95% confidence interval, the (A)s
are the real observed group of fish, the zero (0) line (parallel to the
x-axes) represents the maintenance level, and the perpendicular
line that join both the zero line and the x-axes represents the
maintenance amount of the treatment for each curve]. ................. 31

Theoretical nutrient curve of protein weight (g) in the feed intake vs
protein weight (9) response (gain or lose) by the female of Nile
tilapia O. niloticus fish throughout the experiment period (6
Weeks). [The dotted line is the 95% confidence interval, the (A)s
are real the observed group of fish, the zero (0) line (parallel to the
x-axes) represents the maintenance level, and the perpendicular
line that join both the zero line and the x-axes represents the
maintenance amount of the treatment for each curve]. ................. 34
Theoretical nutrient curve of protein weight (g) in the feed intake vs
protein weight (g) response (gain or lose) by the male of Nile tilapia
O. niloticus fish throughout the experiment period (6 Weeks). [The

viii

10.

dotted line is the 95% confidence interval, the (A)s are the real
observed group of fish, the zero (0) line (parallel to the x-axes)
represents the maintenance level, and the perpendicular line that
join both the zero line and the x-axes represents the maintenance
amount of the treatment for each curve]. ...................................... 35

Theoretical nutrient curve of protein weight (g) in the feed intake vs
protein weight (9) response (gain or lose) by the mixed gender of
Nile tilapia O. niloticus fish throughout the experiment period (6
Weeks). [The dotted line is the 95% confidence interval and the
(A)s are the real observed group of fish]. ...................................... 36

Theoretical nutrient curve of fat weight (g) in the feed intake vs fat
weight (9) response (gain or lose) by the female of Nile tilapia O.
niloticus fish throughout the experiment period (6 Weeks). [The
dotted line is the 95% confidence interval, the (A)s are the real
observed group of fish, the zero (0) line (parallel to the x-axes)
represents the maintenance level, and the perpendicular line that
join both the zero line and the x-axes represents the maintenance
amount of the treatment for each curve] ........................................ 39

Theoretical nutrient curve of fat weight (g) in the feed intake vs fat
weight (9) response (gain or lose) by the male of Nile tilapia O.
niloticus fish throughout the experiment period (6 Weeks). [The
dotted line is the 95% confidence interval, the (A)s are the real
observed group of fish, the zero (0) line (parallel to the x-axes)
represents the maintenance level and the perpendicular line that
join both the zero line and the x-axes represents the maintenance
amount of the treatment for each curve] ........................................ 40

Theoretical nutrient curve of fat weight (g) in the feed intake vs fat
weight (9) response (gain or lose) by the mixed gender of Nile
tilapia O. niloticus fish throughout the experiment period (6
Weeks). [The dotted line is the 95% confidence interval, the (A)s
are the real observed group of fish, the zero (0) line (parallel to the
x—axes) represents the maintenance level, and the perpendicular
line that join both the zero line and the x-axes represents the
maintenance amount of the treatment for each curve]. ................. 41

Theoretical nutrient curve of total ash weight (g) in the feed intake
vs total ash weight (9) response (gain or lose) by the female
gender of Nile tilapia O. niloticus fish throughout the experiment
period (6 Weeks). [The dotted line is the 95% confidence interval,
the (A)s are the real observed group of fish, the zero (0) line
(parallel to the x-axes) represents the maintenance level, and the
perpendicular line that join both the zero line and the x-axes

ix

11.

12.

13.

14.

15.

represents the maintenance amount of the treatment for each
curve] ............................................................................................. 44

Theoretical nutrient curve of total ash weight (g) in the feed intake
vs total ash weight (9) response (gain or lose) by the male gender
of Nile tilapia O. niloticus fish throughout the experiment period (6
Weeks). [The dotted line is the 95% confidence interval, the (A)s
are the real observed group of fish, the zero (0) line (parallel to the
x-axes) represents the maintenance level, and the perpendicular
line that join both the zero line and the x-axes represents the
maintenance amount of the treatment for each curve]. ................. 45

Theoretical nutrient curve of total ash weight (g) in the feed intake
vs total ash weight (9) response (gain or lose) by the mixed gender
of Nile tilapia O. niloticus fish throughout the experiment period (6
Weeks). [The dotted line is the 95% confidence interval, the (A)s
are the real observed group of fish, the zero (0) line (parallel to the
x-axes) represents the maintenance level, and the perpendicular
line that join both the zero line and the x-axes represents the
maintenance amount of the treatment for each curve]. ................. 46

Theoretical nutrient curve of energy (Kcal) in the feed intake vs
energy (Kcal) response by the female of Nile tilapia O. niloticus fish
throughout the experiment period (6 Weeks). [The dotted line is the
95% confidence interval and the (A)s are the real observed group
of fish] ............................................................................................ 49

Theoretical nutrient curve of energy (Kcal) in the feed intake vs
energy (Kcal) response by the male of Nile tilapia O. niloticus fish
throughout the experiment period (6 Weeks). [The dotted line is the
95% confidence interval and the (A) s are the real observed group
of fish] ............................................................................................ 50

Theoretical nutrient curve of energy (Kcal) in the feed intake vs
energy (Kcal) response by the mixed gender of Nile tilapia O.
niloticus fish throughout the experiment period (6 Weeks). [The
dotted line is the 95% confidence interval and the (A)s are the real
observed group of fish]. ................................................................. 51

INTRODUCTION

Tilapia1 have been identified as a major source of animal protein in many
developing countries (Pullin and McConnel 1982). These fish were first cultured in
Africa around 4,000 years ago by the ancestors of the Egyptians (Lee and Newman
1992). Over the last six decades, tilapia have been introduced in many countries
around the world because they are relatively easy to raise under tropical and sub-
tropical conditions. The most important species of tilapia for aquaculture have been
Oreochromis aurea, O. homorum, O. mossambicus, O. niloticus, Sarothemdon
melantheron, Tilapia rendaiii, and T. zillii (Pillay 1990).

Nile tilapia, O. niloticus, appears to have gained a wider acceptability than the
other species by consumers and fish farmers (Guerrero 1978; Pillay 1990; Landau
1992; Avault 1996; Egna and Boyd 1997). The Nile tilapia continues to be one of
the most popular and important aquaculture species in Saudi Arabia. Demand for
this species has increased in spite of its darkish gray coloration, which is often
considered an unattractive attribute by consumers (Pillay 1990; Lee and Newman
1992; Avault 1996; Egna and Boyd 1997).

A number of biological factors have made the various species of tilapia
prime candidates for aquaculture development (El-Sayed et al. 1991; Avault
1996; Egna and Boyd 1997):

1) Tilapia can be fed on a wide variety of natural feeds in extensively managed

 

' Tilapia is a generic term used to describe fish from the family Cichlidae, Genera
Oreochromis, Sarotherodon and Tilapia were originally described as members of the
single genus Tilapia.

ponds (i.e., under natural conditions) including algae, zooplankton, soft green
macrophytes, and invertebrates as well as utilizing poor-quality natural foods
such as blue green algae (King and Garling 1983).

2) Tilapia have been amenable to intensive culture (with the addition of nutrients
and water quality management) in different types of ponds, tanks, and aquaria at
different population densities.

3) Tilapia have tolerated a broad range of water quality conditions. For example,
they have tolerated water temperatures ranging from 10 - 40 °C for extended
periods of time, but grow best in water temperatures of 27 °C (Egna and Boyd
1997). They have survived in water with dissolved oxygen concentrations as low
as 1.0 mg/L (Lee and Newman 1992) and have been raised in fresh, brackish
and sea water.

4) Tilapia readily utilizes artificial feeds, and compared to many cultured fish,
grow rapidly on low protein feeds.

5) Tilapia breed reliably in captivity (Lee and Newman 1992).

6) Tilapia have exhibited a high level of disease resistance and have been
handled with a minimum of stress.

Some biological constraints associated with tilapia aquaculture have also
been observed. The main constraint to intensive aquaculture of tilapia has been
their early sexual maturation and frequent breeding. Tilapia have been shown to
breed monthly when they reach sexual maturity (Lee and Newman 1992). Fry
from unintended natural production after stocking has had a negative effect on

growth under culture conditions because of the increased competition for feed

and oxygen. Furthermore, unintended fry have complicated the management of
culture ponds by making it difficult to maintain accurate inventories, project
growth rates, and control feeding.

Many researchers have suggested producing all-male populations to avoid
overpopulation of tilapia in aquaculture and to increase production since male
tilapia grow faster and attain a larger size than females when stocks are mixed
(Pillay 1990; Ridha and Lone 1990; Avault 1996). All-male stocks have been
produced by the following: 1) manual sexing (Egna and Boyd 1997), 2) using of
androgenic hormones to sex reverse females (Hickling 1968; Semakula and
Makora 1968; Shell 1968; Ridha and Lone 1990; Phelps et al.1992; Phelps at al.
1995), 3) inducing triploids (Varadaraj and Pandian 1990; Hussain et al. 1995), 4)
producing YY-supermale (Scott et al. 1989), and 5) hybridization (Lagler and
Steinmentz 1957; Hickling 1960; Al—Daham 1970).

Other methods to reduce reproduction have included combined stocking
of tilapia with piscivorous predators (Swingle 1950, 1960; Bardach et al. 1972;
Dunseth and Bayne 1978; Wohlfarth and Hulata 1983; Ofori 1988), cage culture
(Pagan 1969; Siraj et al. 1988; Lovshin and Ibrahim 1988; Mair et al. 1995), and
high intensive culture systems (Swingle 1960; Avault 1996).

This experiment was designed to determine the effects of gender on
performance and growth of the Nile tilapia, Oreochromis niloticus, in mixed and
separate gender stocks using a saturation kinetics model developed by Morgen
et al. (1975). The model was based on enzyme kinetics equations developed by

Michaelis and Menten (1913) and Hill (1911). The general equation was based

on physiological responses to different environmental factors. The fundamental
basis of this model was the interaction between an independent variable, nutrient
intake (I), and a dependent variable, the observed response (r), as described by
the equation:
b (Kris)n T Rmax In
(Ko.s)" "‘ I"

r:

 

Where:

r = observed response of the fish (body weight gain or nutrient deposition at
specific intake level per day),

b = ordinate intercept,

KM, = nutrient constant (nutrient at ‘/2 of Rm“),

Rm, = maximum response,

n = slope factor (compared to K”, apparent kinetic order of the response with
respect to l as I" becomes negligible ),

l = nutrient intake.

The model has been experimentally tested to measure net nutrient
deposition, plasma nutrient levels, weight gain, tissue enzyme kinetics, dietary
requirements and other physiological processes for many animals such as rats,
mice, chickens, turkeys, fish and humans (Mercer, 1980, 1992; Belal, 1987; Belal
et al. 1992; Mercer et al. 1996). This, or similar models, have been used to
determine optimum feeding levels, standard metabolic rate, protein and energy

requirements, and growth response for tilapia fed upon natural and artificial

feeds. Because of inexpensive equipment and a relatively short time period
required, this model could be used in most developing countries to determine the
nutritional responses of fish to feeds. In addition, this model could be used to
determine basic bioenergetic requirements of fish and to predict the production

response of fish to a specific diet.

LITRATURE REVIEW

More than 70 species and sub-species of tilapia have been used or are
potential candidates for aquaculture Egna and Boyd (1997). Chimits (1955)
reported that both the genus of Tilapia and Oreochromis had about 100 known
species, which originated in Africa and extended north to Jordan. Based on
meristic, ethological, and morphological characteristics, Trewavas (1966, 1973,
1980, 1982a,b) divided the genus Tilapia sensu late! into three genera Tilapia,
Sarctherodon, and Oreochromis based on parental care extended to eggs and
larvae. All three genera initially spawned eggs in nests. Species of the genus
filapia were defined as those species that continued parental care of their
offspring in nests, while the genus Sarctherodon were paternal or bi-parental
mouthbrooders, and the genus Oreochromis were maternal mouthbrooders
(Pouyaud and Agnese 1995). Pouyaud and Agnese (1995) concluded that the
Tilapia senso stn‘cto had the largest number of ancestral characters, which
confirmed the hypothesis that mouthbrooders (Oreochromis and Serotherodon)
arose from substrate spawners.

Early sexual maturation is a physiological characteristic of tilapia. Lee and
Newman (1992) and Avault (1996) observed that tilapia reached sexual maturity
as early as two months of age or at a length of 6 cm (2.4 inches). Mature tilapia
commonly spawn from early spring until late fall and the female can spawn
repeatedly during one spawning season. The optimum temperature for breeding

is in the range of 24 to 29 °C (Lee and Newman, 1992; Egna and Boyd 1997).

Frequency of spawning and the age and size of the female have been identified
as limiting factors that contribute to the number of eggs produced. These
characteristics have created problems for commercial tilapia farmers because
they reduce growth and feed conversion and it is impossible to keep an accurate
inventory to calculate appropriate rates.

Many researchers have developed methods to control and manage the
problems of early sexual maturation. Because male tilapia may grow faster than
the female (Egna and Boyd 1997, Siddiqui et al. 1997), many researchers have
developed techniques to produce all-male populations. Abucay and Mair (1997)
suggested that all-male tilapia culture was important for more unifome sized fish
and higher yields. Preventing overpopulation in tilapia culture could be achieved
by manually sorting the males and the females based on secondary sex
characteristics, sex reversal, androgenic hormones, hybridization, stocking tilapia
at high densities, stocking tilapia with natural predators, by induction of
polyploidy, and by production of superrnales (YY).

Manual sorting is one of the simplest ways to segregate males from
females (Egna and Boyd 1997). However, there 'are some disadvantages to this
method. First, only large and mature fish can be accurately sexed because it is
hard to distinguish genders in young fish that are not ready for spawning.
Moreover, keeping only the males and discarding the females result in using only
approximately half of the fish. The fish also suffer from stress because of the
handling process. For large-scale production, this technique has not only been

time consuming but also required experienced laborers, which increased the

production budget.

Successful sex reversal techniques have been developed for tilapia using
various androgenic hormones (Camerino and Sciaky 1975). Sex reversal
techniques have been practiced for many decades. Females have been
converted to functional phenotypic males. Androgenic hormones have been
applied either by injection or by oral administration in the diet. There are many
factors that can impact the application of androgen hormone treatments such as
fish species, fish age at administration, type and dosage of hormones and
duration of treatment (Hickling 1968; Semakula and Makora 1968; Shell 1968;
Guerrero 1975; Lovshin et al. 1990; Ridha and Lone 1990; Phelps et al. 1992,
1995). There have been, however, some major practical disadvantages for fish
farmers. Injection of the androgenic hormones has caused handling stress to the
fish. The process was labor intensive and required experienced workers. Sex
reversal using androgenic hormones has not been 100% effective. The high cost
of hormones and labor may not be affordable for many farmers, especially in
developing countries. Furthermore, hormone treated feeds may not be effective
when applied in the earthen ponds or lagoons where there are natural food
sources. Thus, in order to insure that fry have consumed the hormone treated
feed, tilapia should be fed treated feeds in tanks, not in ponds. However, Buddle
(1984), Phelps and Cerezo (1992), and Phelps at al. (1995) reported that the
efficiency of the androgen treatment was not affected in the presence of the
natural feed. Androgen treatment has resulted in anatomic and morphological

deformities in fish. It has caused deformities of the jaws and mouth, head and

gonad abnormalities, exposed gills, short operculum, and liver malformations
(Clemens and Inslee 1968; Pandian and Varadaraj 1987; Ridha and Lone 1990).
However, Egna and Boyd (1997) did not observe any gross abnormalities of the
fish in any of their studies. Finally, hormone treatments may also be of concern
to consumers. Anabolic hormones are controlled substances and have not been
approved for use in fish feeds in the USA. Currently, an lnvestigational New
Animal Drug (INAD) permit has been issued to Auburn University by the Federal
Drug Administration for efficacy and safety testing of these hormones for sex
reversal in tilapia with the ultimate goal of approving them for this use in fish
feeds.

Thorgaard (1983) reported that sterile triploid fish exhibited faster growth
than diploid fish. However Bramick et al. (1995) observed no differences in
growth between triploid and diploid Nile tilapia until they reached the age of
maturation. Pandian and Varadaraj (1988) found that the ovaries of triploid
female tilapia were markedly underdeveloped while the size of the testes of male
triploids were not affected. Pandian and Varadaraj (1988) observed that the
female triploid tilapia grew 14% faster than the sex-reversed male and 23%
faster than the male triploid. Bramick et al. (1995) observed that after 285 days
the average body weight of both triploid Nile tilapia males and females were
significantly greater than diploids of the same sex. Brélmick et al. (1995)
recommended raising triploid Nile tilapia whether these fish were males or
females. Others, such as Mair et al. (1995) have concluded that cultivation of

polyploidy Nile tilapia males rather than mixed-sex fish could increase production

by 34%. In general, most studies agreed that mono-sex stocks had a higher
potential yield production than mixed-sex stocks.

Varadaraj and Pandian (1989), Purdom (1993), Tave (1993), Egna and
Boyd (1997) have described the procedures for superrnale (YY) production.
Sexually undifferentiated fry were fed a diet containing estrogen hormone to
produce sex-reversed females. Sex —reversed females are phenotypic females
that are genetic males. The offspring produced by feeding estrogen treated diets
were a mix of normal males (XY), normal (XX) females, and sex-reversed (XY)
females. The sex-reversed females were separated from the normal female
genotype by analyzing the sex ratio of their offspring. Crossing a normal male
with a normal female resulted in an approximately 50:50 sex ratio of phenotypic
males to females. Crossing a normal male with a sex-reversed female produced
an approximately 75:25 ratio of phenotypic males to females (50 XY: 25 W: 25
XX). Superrnales and normal male were identified by analyzing their offspring
when crossed with normal females. Although the process has been successfully
demonstrated, it required a significant investment of time and resources to
produce and identify sex-reversed females and supen'nales. The resources and
time required are beyond the ability of most fish culturists especially in
developing nations.

Hybridization is another method that has been used to a limited extent to
effectively manage tilapia reproduction. It can be used to produce all-male tilapia
(Egna and Boyd, 1997). All-male hybrids have resulted from crossing of a

homogametic female and a homogametic male (Pruginin et al. 1975; Lovshin

10

1982). The first generation of tilapia hybrids with T. homorum have produced all
or nearly all-male populations. In general, hybrids have grown faster and larger
than either parent. One of the most commonly used hybrid tilapia crosses has
been between male Tilapia homorum X female T. nilotica that produced all or
nearly all-male offspring. Production of hybrid tilapia has a number of practical
disadvantages. Maintaining separate stocks of “pure” species and hybrid
offspring is difficult since there may be little difference in morphological
characteristics between the parent stocks and their subsequent hybrid offspring,
especially in later generations (Egna and Boyd, 1997). Tilapia species readily
hybridize, so it has become difficult to obtain the pure species.

Tilapia have been reared at very high densities (super intensive culture
systems) in tanks, ponds, or raceways to inhibit reproduction and to enhance
production. Tilapia normally exhibits aggressive territorial behavior during
breeding. The male defends a territory around his nest to prevent predation of
the eggs or young. If males cannot defend a territory, they may not build nests
and breed with females. However, crowded fish populations require special
management to provide enough feed while maintaining sufficient dissolved
oxygen and safe and adequate water quality.

Predaceous fish have also been used as a method to control
overpopulation in tilapia production ponds (Bardach et al. 1972; Dunseth and
Bayne, 1978; Popma, 1982; McGinty, 1985; Wohlfarth and Hulata, 1983; Egna
and Boyd, 1997). Predator fish such as the largemouth bass (Micropterus

salmoides), jewel fishes (Hemichromis spp.), Guapote tiger (Cichlasoma

ll

manauense), peacock bass (Cichla ace/Ian‘s), snakehead (Ophicephalus spp.),
crappies (Pomoxis spp.), and bowfin (Amia calva) have been suggested to
control the overpopulation of tilapia in the polyculture system. The predators
usually consumed the eggs, fry, and fingerlings that were produced by tilapia.
Predators should not be larger than the juvenile tilapia initially stocked in the
pond, otherwise the tilapia will become easy prey to the predators.

This study was designed to determine the effects of tilapia gender on
performance and growth in separated and mixed-sex using a saturation kinetic
model developed by Morgen et al. (1975). Using enzyme kinetic equations, Hill
(1911) and Michaelis and Menten (1913) developed this model. It is also based
on physiological responses to different environmental and nutritional factors. The
model concept is built on the interaction between a dependent variable, the
observed response (r), and an independent variable, nutrient intake (I). This
model was derived from complicated formulas. The basic step is that any
nutrient (l) given to any animal creates a certain response (r), whether negative
or positive. For example, a nutrient (I) given to an animal, a specific receptor (M)
will respond to yield the complex (Ml), which produces a physiological response

(pr) in a proportional manner to concentration of (MI), as follows:

 

 

K1

I + M <=======> MI (1)
K2

pr = K3 [MI] (2)

(Where K1, K2 and K3 are constants and [] denotes concentration).

At equilibrium, the combination of the above equations is written as follows:

12

[M] ['1 K2
= = Kl
[Ml] K1

 

(Where Kl is also a constant)
Thus, for the total receptor concentration (Mt), where [Mt] = [M] + [Ml],
or

[M] = [Mt] - [Ml], then:

[Mt - MI] [I]

 

= Kl
[Ml]

After rearranging, it gives:

[MI] _ [I]
[Mt] Kl + [l]

 

When all receptors are occupied, the maximal physiological responses of the

system (PRmax) are:

 

PRmax = K3 [Mt] (3)
Then:

pr [Ml]

PR...” - [Mt]

 

 

PRmax ['1
K1 + [I]

From this equation, comes the linear model (straight-line) equation of

 

 

pr (4)

13

Michaelis-Menten (1913), Hegsted and Neff (1970), that is:

Y=aO+a1X (5)

 

There are two limitations to equation 4 that logically and practically do not
match the observed responses. First, responses are found experimentally to be
sigmoidal, but this equation only describes a hyperbola. Adding the parameter n
to the equation may solve this limitation:

PR..." [l]"

pr = (6)
KI "’ III"

 

 

(Where n is the apparent kinetic order)
As n increases above 1, the curve of this equation fluctuates from a hyperbola to
a sigmoidal (n > 1). This equation is known as the “ Hill equation” which has
been utilized in enzyme kinetics (Hill 1911).

The second limitation to this equation is in regard to the (X, Y) coordinate
system, which describes a curve that passes through the point of origin (0, 0) and
does not predict responses such as weight loss. To solve this, it is necessary to

add the parameter b (the intercept on the ordinate y—axis) to the previous

 

 

 

 

equafion:

PR...“ [|]"
pr = + b (7)

In + lfl"
Then:
PR...“ [I]" + b k1 + bl"
pr = (8)
kl "' “I"

14

If (PRmax + b) = Rm”, and simplify pr to r, the four-parameter mathematical
model for physiology response could be then:
b k. + Rm, [l]"

r= (9)
k. + “I"

 

 

This may be written:

b(K0.5)n 1' Rmax [lln

 

 

r = (10)
[Ko.s]" + ill"

where:

r = Physiological observed responses in the fish,

b = intercept on the ordinate y - axis,

K“, = intake constant for ‘/2 of Rm“,
R...“ = maximum responses,
n = slope factor ( compared to K”, apparent kinetic order of the response
with respect to l as I" becomes negligible),
I = nutrient intake.

This model has been used as a successful'test tool with different animals
such as mice, rats, turkeys, chickens, fish and humans (Mercer 1980; Belal 1987;
Mercer et al. 1989; Belal et al. 1992; Mercer 1992; Mercer et al. 1993, 1996). It
was used to estimate weight gain, nutrient deposition, dietary requirements,
plasma nutrient levels, net nutrients, tissue enzyme kinetics and other
physiological processes. Belal et al. (1992) studied two practical feeds fed to

Oreochromis niloticus fingerlings by applying the saturation kinetic model.

15

Including this model, there are other models that have been used for the
determination of the standard metabolic rate, optimum feeding levels, growth
responses and protein energy requirements for tilapia fed both natural and
practical feeds. Annett (1985) used a similar threshold-corrected hyperbolic
model to demonstrate the relationship of the specific growth rate of Tilapia zillii to
three different feeds. He also used this model to determine the relationship

between the fish growth to fish size and water temperature.

16

METHODS AND MATERIALS

This study consisted of three experiments to determine the effects of
gender on growth and performance using the saturation kinetics model. Male,
female, and mixed-genders groups, respectively, were studied in separate
feeding trials. All three feeding trials were conducted after an initial acclimation
period at the Aquaculture Laboratory, Department of Fisheries and Wildlife, at
Michigan State University. The female-gender feeding trial was conducted
followed by concurrent feeding trials for the male and mixed-gender groups.
Each feeding trial took six weeks.

Ten-gallon glass aquariums were used as the experimental unit. Six fish
were stocked in each aquaria with three replicated tanks for each feeding level
for a one week acclimation period. All fish were fed to satiation twice each day
during the acclimation period. After the one week acclimation period, the six fish
in each aquaria were-weighed as a group to determine the initial weight. Fish
were weighed every two weeks in order to adjust feeding rates until the end of
the feeding trial. Aquaria were cleaned on a daily basis throughout each feeding
trial. On the last day of each feeding trial experiment, fish from each aquarium
were weighed, to determine final weight, and were euthanized using Tricaine
methane sulfonate (MS-222). Fish were ground and stored frozen for

subsequent analysis.

17

FISH

Oreochromis niloticus fingerlings were used as the experimental fish.
They were obtained from Illinois State University at Normal. Fish were held at
the Aquaculture Laboratory, Michigan State University for at least two weeks in
order to acclimate to their new environment. During that time, fish were sexed
based on primary characteristics by squeezing the ventral side of the fish, just
anterior to the urogenital duct to test for gamete production and separated into
three gender groups: (1) males, (2) females, and (3) unidentified sex (no
gametes were observed).

Six fingerlings, 7.5 - 9.0 cm (3.0 - 3.5 inch), were randomly assigned to
each tank. Fish for each gender group were randomly selected from holding
tanks containing male or female fish. Each tank was covered with plastic mesh
to prevent them from jumping out of the tanks. Fish were fed at satiation level
twice a day for a one week acclimation period. After the acclimation period, fish
were weighed as a group to determine initial Weight. An additional group of 12
fish were euthanized using Tricaine methane sulfonate (MS-222), ground, and

stored frozen for subsequent proximate analysis.

FEED AND FEEDING

A fresh commercial trout diet (PURlNA lot number 5106), containing
protein not less than 40% and fat not less than 10%, was fed throughout the
feeding trials. Feed was ground to the proper size for the fingerlings then kept

frozen to be used for the experimental feeding trial fish groups. Feeding levels

18

were based on the percentage of the wet body weight for the fish, and adjusted
every two weeks. The feed was fed on a dry weight basis at 0.5, 1.0, 2.0, 4.0,
and 6.0% of the total wet weight per tank per day. The low feeding levels (0.5
and 1.0%) were fed once per day, while the higher feeding levels (2.0, 4.0 and
6.0%) were fed half of the total amount twice per day every 8 -14 hours. Three

replicates for each feeding level were used.

WATER

Well water heated to 26 :l: 2 °C (77- 81 °F) and supplied by a single pass,
flow through culture system. The average water exchange rates were 30.6 L/h
(8.1 gal/h). Dissolved oxygen, temperature, and pH were measured in each
aquarium daily which ranged from 3.75 - 6.05 mg/L, 26 1 2 °C, and 6.3 - 6.7
respectively. Dissolved oxygen and temperature were measured using a YSl 55
meter. Ammonia concentrations were measured weekly and ranged from 0.03 -
0.045 mg/L. The pH and ammonia concentrations were measured using 3 Fisher
Scientific, Accumet model 25 pH/ion meter and the appropriate probes and
standards for calibration. Each morning, solids (feces, food and other residues)
were siphoned from the bottom of the culture tanks. There was no fish mortality

throughout the feeding trials.

PROXIMATE ANALYSIS
At the beginning of a feeding trial a sub-sample of 12 fish were

euthanized, which were considered to be a control fish sample. At the

19

completion of each feeding trial, the remaining fish were euthanized. MS-222
was administrated at rate of 1 g/ 4 L of water. All the fish were ground and
stored frozen at the temperature of - 7.0 to - 8.0 °C (17 — 19 °F). Proximate
analysis of fish and feed samples were determined using standard AOAC (1990)
methods for moisture, crude protein, crude fat, total ash, and total gross energy
as dry matter basis. Moisture was determined from a one 9 subsample at a
temperature of 105 t 1 °C (219 - 223 °F) overnight. Total ash was determined
using a muffle furnace for 18 hours at a temperature 550 °C (1022 °F). A micro-
Kjeldhal system (Labconco Rapid Kjeldahl System) was used to measure the
crude protein. Crude fat was measured by using Ether Extraction. Finally, a Parr
1241 Bomb Calorimeter was used to determine gross energy values (Lovell

1975).

STATISTICAL ANALYSIS:

The saturation kinetic model (equation 10), which was developed by
Mercer et al. (1980) was used to estimate the four parameters (Rmu, K”, n and
b) and the maintenance level of five variables (growth, crude protein, crude fat,
total ash, and gross energy) for the three gender groups. This model was
developed on the SYTAT software CD and provided by Dr. Mercer, Department
of Nutrition, University of Kentucky at Lexington, KY. Along with the above four
parameters, this model also calculated other measurements. Including the
degrees of freedom, the residual standard error, student t-value, and the 95%

confidence interval. Using the student t-distribution, the upper 95% quantile with

20

11 degree of freedom (sample size - # of parameter 15 — 4 = 11) is 1.8. Any t-
value for each parameter (Rmx, K05, n and b) for all the five variables of the

three gender groups greater than 1.8 in absolute value would be considered to

be significant.

21

RESULTS

Dietary and nutrient response curves were developed for different gender
groups of O. niloticus fed varying levels of the same commercial diet for six
weeks. The shape of the curve (n), the curve parameters (Rmx, Ko,5, b), and
calculated maintenance level (ML) varied between gender groups. Feeding rate,
nutrient level intake (feed fed throughout the 6 week experimental period), and
observed response (weight gain or net nutrient deposition) are summarized in
Table 1 and Appendix Tables 1 - 4. The proximate analysis of feed and fish from
each male, female and mixed-gender group of O. niloticus (Table 2) were used to
calculate intake and response relationships for protein, fat, ash, and gross
energy (Table 3). The calculated parameters for growth, protein fat, ash and
gross energy are summarized in Table 4. These calculated parameters were
used to generate nutrient response curves for‘the three gender groups. Each
point on the nutrient response curves in the following sections represents an
observation from an individual tank. The dotted lines represent the 95%
confidence interval. All the points below the intake (I) axis are in negative
balance while all the points above the l axis are in positive balance (Drapper et
al. 1966). The mixed-gender group was observed to have the wider confidence
range compared to the other groups. All the gender groups grew markedly better
at higher feeding rates (2.0.4.0 and 6.0%). At low feeding rates (0.5 and 1.0%),

there was a depression in the growth responses.

22

Table 1.

The initial weight, final weight, weight gain and feed fed to female, male, and

mixed gender groups of O. niloticus over a six week experimental period.
Each value represents the mean and standard deviation for three replicate
tanks per feeding rate percentage.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Gender group Feeding Initial Weight Final Weight Weight Gain Feed Fed
Rate % (9) (9) (9) (9)
106.8 3 1.4 114.7 3 2.6 7.6 3 1.3 22.9 3 0.8
Female 0.5
10 12153190 13153169 10.0350 51937.6
2 0 110.5 3 11.3 163.3 3 4.9 52.6 3 7.7 103.2 3 2.4
4 0 128.7 3 7.2 232.7 3 5.7 104.0 3 4.1 275.6 3 13.1
6 0 131.5 3 12.4 307.7 3 6.3 176.2 3 9.5 480.j8 3 8.9
Male 05 125.6 3 6.9 126.7 3 7.7 2.6 3 0.6 26.3 3 1.4
1 0 130.0 3 5.4 154.0 3 8.7 24.0 3 12.5 55.3 3 1.6
2 0 127.0 3 10.9 215.0 3 23.9 no 3 17.6 130.7 3 13.6
4 0 106.0 3 17.9 - 263.0 3 22.6 155.0 3 24.3 261.5 3 16.4
6 0 129.2 3 10.1 334.2 3 6.6 205.0 3 14.6 515.6 3 33.0
Mixed Gender 05 136.3 3 3.5 137.3 3 2.5 1.0 3 1.0 26.6 3 0.8
1 0 120.2 3 24.7 146.5 3: 36.0 26.3 3 11.6 54.2 3 12.0
2 0 106.6 3 31.2 203.53 61.6 94.7 3 35.6 110.3 3 31.7
4 0 121.5 319.6 252.2 3 11.6 1%] 3 8.1 265.9 3 38.0
6 0 129.3 3 6.5 301.8 3 fi 172.5 3 5.2 432.3 3 26.0

 

 

 

 

 

 

23

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

24

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25

Table 3. The proximate analysis of female, male. and mixed gender groups of O.
niloticus fed varying rates of feed over a six week experimental period. Each

value represents the mean and standard deviation for three replicate tanks

per feeding rate percentage. All percentages are on a dry matter basis.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Gender group Feeding Protein Fat Ash Moisture Gross
Rate % (%) (%) (%) (%) Energy
(Kcal/g)
46.3 1 1.2 3.9 1 0.4 8.6 1 0.7 45
Feed
. . 56.8 1 0.5 8.6 1 0.5 18.4 1 0.8 75.1 1 0.4 1.7 1 0.4
Female Initial
0 5 53.5 1 1.3 2.5 1 0.9 14.8 1 0.2 76.2 1 1.3 1.2 1 0.03
1 0 56.3 1 0.3 9.9 1 0.4 16.8 1 0.4 73.6 1 0.8 1.7 1 0.6
2 o 57.1 1 0.3 15.9 1 2.9 20.5 1 3.1 69.9 1 0.4 2.4 1 0.05
4 0 59.6 1 1.1 21.4 1 1.8 26.3 1 0.9 6H) 1 0.4 3.2 1 0.9
6 o 62.5 1 1.3 24.0 1 0.5 35.2 1 2.9 67.4 1 1.3 4.7 1 1.0
. . 57.84 8.59 18.4 75.1 1 0.4 1.7 1 0.4
Male Initial
0 5 55.3 1 0.6 6.0 1 3.1 16.4 1 0.1 74.9 1 0.7 1.2 1 0.02
10 56610.5 10.7110 17.1105 737181 1.8 1.91 0.2
2 0 57.6 1 0.4 18.8 1 0.7 21.4 1 1.2 73.3 1 3.1 2.9 1 0.5
4 0 58.8 1 0.8 21.4 1 1.0 25.6 1 1.3 72.1 1 2.7 3.9 1 0.6
6 0 60.4 1 0.3 31.8 1 2.8““522 1 7.0 68.9 1 2.1 5.7 1 0.5
Mixed Gender Initial 1'7 t 0'4
0 5 59.2 1 3.5 7.0 1 0.3 13.7 1 0.5 74.5 1 0.4 1.4 1 0.1
10 58213.2 15914.2 16711.0 72711.2 1.9 1 0.6
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40 59210.3 30.4177 24811.1 69.1101 4.2 11.1
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26

 

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27

GROWTH

The estimated growth response using the saturation kinetics model
parameters (Table 4) is presented in Figures 1 - 3. The R...ax for growth was
significantly different among the gender groups (Table 5). The male-gender
group had the highest predicted growth response (Rmax = 218.8) followed by the
female-gender group (Rm, = 202.4 g) and the mixed-gender group (Rm = 189
g). The K01. was highest for the female-gender group (Ko,5 = 229.4 g) followed by
the male-gender group (K05 = 157 g) and the mixed-gender group (K05 = 132.3
g). The kinetic order of the curve (n) can be used to describe the shape of the
line. When n equals one (n = 1) the shape of the curve is a hyperbola. When
kinetic order of the curve is greater than one (n > 1), the curve is sigmoidal.
From the estimated curves for growth, all the gender groups were in a sigmoidal
shape. The highest n was 2.1 in the male-gender group, followed by the female-
gender group (n = 2.0) and the mixed-gender group (n = 1.7). The estimated
dietary response at zero feed intake level (b) was the highest for female-gender
group (b = 6.3 9) followed by the male-gender group (b = — 5.4 g) and the mixed-
gender group (b = —5.7 g. The predicted maintenance level (ML) for growth for
the male-gender group was 26.9 g, which was at a feeding rate of approximately
0.5% of the total weight body weight of the fish. The mixed-gender group ML for
growth was predicted at 16.87 g, which was around 0.3% of feeding rate. There
was no estimation of ML predicted for the female group because the predicted

curve does not intersect the x-axis.

28

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32

CRUDE PROTEIN

The protein response curves using the Saturation Kinetics Model
parameters (Table 4) predicted are illustrated in Figures 4 - 6. The maximum
theoretical amount of protein deposition in the fish bodies (Rum) was significantly
different for all the gender groups (Table 6). The Rm, of protein deposition for
the female-gender group was 53.6 9 followed by the male-gender group (Rm, =
51.2 g) and the mixed-gender group (Rum = 48.7 g). The predicted K05 was
highest for the female-gender group (K05 = 109.9 9) followed by the male-gender
group (Ko.s = 101.5 g) and the mixed-gender group (Ko.5 = 79.4 g). The kinetic
order of the curve model for the protein deposition for all gender groups were
sigmoidal (n > 1). The predicted n parameter for all the gender groups were not
significantly different (male-gender n = 1.8, female-gender group n = 1.7, and
mixed-gender group n = 1.6). The dietary response of protein deposition at zero
feed intake level (b) varied significantly among the fish gender groups. The
lowest b value was -1.6 g in the male-gender group followed by the female-
gender group (b = —1 .1 g) and the mixed-gender group (b = 2.5 g). The
predicted ML for dietary protein level was significantly different among male and
female-gender groups. The male—gender group had the highest ML of 14.8 g,
which was about 0.6% of feeding rate of protein per six weeks followed by the
female-gender group (ML = 11.17 g and approximately 0.47% of protein fed per
six week period) and the mixed-gender group was not predicted because the ML

was less than 0.

33

 

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37

CRUDE FAT

The response curves for fat deposition using the Saturation Kinetic Model
(Table 4) are presented in Figures 7 - 9. The predicted Rmax for fat deposition
were significantly different for all the gender groups (Table 7). The Rm, for the
mixed-gender group was 45.5 9 followed by the male-gender group (Rm, = 36.9
g) and the female-gender group (Rm, = 23.6 g). The K05 were significantly
different among all gender groups. The highest predicted K05 for fat was 10.7 g
for the male-gender group followed by the mixed-gender group (K05 = 8.2 g) and
the female-gender group (K05 = 7.4 g). The kinetic order (n) for the fat deposition
curve predicted that all the gender group curves were sigmoidal (n > 1) and not
significantly different. Both the mixed and the female-gender groups, the n
parameter was 1.8. The n value of the male-gender group was 1.9. The fat
deposition responses at the zero of dietary feed intake (b) were significantly
different among gender groups. The lowest b parameter was —1.8 g for the
female-gender group followed by the male-gender group (b = — 0.8 g) and the
mixed-gender group (b = - 0.4 g). The ML for fat deposition for all the gender
groups was significantly different. The lowest predicted ML was for the mixed-
gender group (ML = 0.59 g of fat per six week) followed by the male-gender
group (ML =1.42 g of fat per six week) and the female-gender group (ML = 1.77 g

of fat per six week).

38

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42

TOTAL ASH

The estimated ash response using the Saturation Kinetic Model
parameters (Table 4) for all the gender groups are presented in Figures 10 -12.
The R...” for total whole body ash were significantly different among all gender
groups (Table 8). The highest predicted Rm, was for the male-gender group
(Rm, = 40.3 9) followed by the female-gender (Rm, = 36.5 g of ash) and the
mixed-gender group (Rm, = 27.6 g). The predicted K”, for total body ash was
significantly different for all the gender groups. The highest predicted KM, for
total ash was for the male-gender group (Ko.5 = 29.5 9) followed by the female-
gender group (KM, = 25.8 g) and the mixed-gender group (KM, = 15.5 g). The
predicted kinetic order (n) for the total body ash predicted that all the curves for
the gender groups were sigmoidal (n > 1). The highest predicted n was 2.3 for
the female-gender group followed by the male-gender group (n = 1.8) and the
mixed-gender group (n =1.7). The total ash deposition response at the zero of
dietary feed intake (b) was significantly different for all gender groups. The
highest predicted b parameter was — 0.5 g for the female-gender group followed
by the male-gender (b = - 0.8 g) and the mixed-gender group (b = -1.3 g). The
predicted ML for total ash deposition was significantly different for all the gender
groups. The highest predicted ML for total ash was 4.0 g of ash per six weeks
for the female-gender group followed by the male-gender group (ML = 3.34 g of

total ash per six week) and the mixed-gender group (ML = 2.3 g).

43

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47

GROSS ENERGY

The estimated theoretical total energy deposition response (Kcal) using
the Saturation Kinetic Model (Table 4) for each gender group are presented in
Figures 13 -15. The predicted Rm, for total body energy deposition were
significantly different for all the gender groups (Table 9). The highest Rm, was
183.1 x10‘Kcal of energy predicted for the male-gender group. The predicted
Rm, for female-gender group was 174.2 x 10‘ Kcal. The lowest Rm“ was 168.4
x 10‘ Kcal of energy for the mixed-gender group. The predicted KM, was
significantly different for all the gender groups. The highest Ko,5 for energy
deposition was 86.9 x 10‘ Kcal predicted in the female-gender group followed by
the male-gender group (KM, = 72.9 x 104 Kcal) and the mixed-gender group (K05
= 69.3 x 10‘ Kcal). The kinetic order (n) for the energy curves were not
significantly different among the three gender groups. All predicted response
curves for the gender groups were sigmoidal (n > 1). For both the female and
the mixed-gender groups, the predicted n was 1.7. The estimated kinetic order
(n) of the energy for the male-gender group was 1.6. The dietary response of net
energy at zero feed intake level (b) was significantly different among the fish
gender groups. The lowest predicted b was 24.9 x 10‘ Kcal of net energy for the
female-gender group followed by the male-gender group (b = 26.1 x 10‘ Kcal)
and mixed-gender group (b = 31.2 x 10‘ Kcal). The predicted ML for dietary
energy for all gender groups was greater than zero (Figures 13 — 15 and Table

4).

48

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52

DISCUSSION

The primary goal of this study was to use the saturation kinetic model
(Morgan et al. 1975) to describe 0. niloticus weight gain and net nutrient
deposition as a function of nutrient intake by gender. The physiological response
variables tested (weight gain, protein deposition, fat deposition, total ash
deposition, and net energy deposition) were used to generate the saturation
kinetic models (Figures 1-15 and Table 4). Responses could be calculated at
any intake level using the model equation after estimating the parameters (Rm,
KM, n, and b) and ML. Each of these parameters interacts with one anther either
directly or indirectly. Rm“, K05, n, and b define the response by the following
equafion:

b (Ko,5)" + Rm“ I"

(Ko.s)" + I"

r:

 

The second goal of this study was to use the model parameters to
determine differences in basic nutritional requirements between the gender
groups of O. niloticus. To compare responses between gender groups, all

parameters and interactions must be considered.

GROWTH

Previous studies on cultured tilapia species have indicated that growth
and performance were varied between mono-sex and mixed-sex cultures. For
instance, Torran and Lowell (1986) reported that the growth rates and mean

weights for male and female in mixed-gender population of Oreochromis aureus

53

 

“3.1.0.2001...“ - I-

tilapia stocked into channel catfish (Ictalurus punctatus) grow out ponds were
2.06 and 1.72 9 [day and 249 and 211 g, respectively.

The hypothesis for growth for this study was that the intake-response
curves would be equal for all gender groups (male, female, and mixed-gender).
The results indicated that the responses were not equal between gender groups.
In this study, growth and performance between gender groups were varied. In
general, the responses by the male-gender group were superior compared to the
other groups (the female and the mixed-gender groups). The maximum
theoretical response for growth (Rum) can be used to estimate the genetic
growth potential of fish relative to feed intake. As the responses approach Rmax
the nutrient causing that response becomes less limiting. This will continue until
limitation on the response passes to some other non-nutritional source such as
the genetic potential of the fish. Similar growth responses were observed using
the saturation kinetics model by Belal et al. (1992) when they compared the
growth rates of O. nilotica fed diets from different countries.

Superior male tilapia growth rates have been reported by Van Someren
and Whitehead, (1960); Fryer and lies (1972); Kubaryk (1980); Egna and Boyd,
(1997); Siddiqui et al. (1997); Abucay and Mair, (1997). The results of this study
are in agreement with these previous studies. The theoretical maximum
response (Rum) value was (218.8 g) for the male-gender group, was significantly
highest among the other groups. Surprisingly, the mixed-gender group had the
lowest predicted response (189.0 9). Size variance was observed for fish in the

mixed-gender group. Furthermore, the response curves from our study indicated

54

that the mixed—gender group had wider confidence limits than the other gender
groups. The wider 95% confidence limits for mixed-gender group might have
been the result of gender variation.

Mair et al. (1995) observed a 34% increase in male tilapia production
compared to mixed-gender production. They confirmed that all-male populations
resulted in higher yields of marketable fish than mixed-gender populations.
Comparing the growth rates of all-male and all-female of Tilapia nigra
populations, Van Someren and Whitehead (1960) found that the separation of
sexes did not affect the faster growth of the males. This superiority of male
growth is due to genetic, environmental, physiological, and behavioral reasons.
Goudie et al. (1995) suggested that there is a major influence of sex on growth
that must be considered to evaluate the role of the genes related to growth along
with the environmental factors. Also, Fryer and lies (1972) studied Tilapia aurea,
and they concluded that along with the environmental factors that moderated the
male growth superiority, genetic basis is a considerable factor could influence the
growth.

McGinty (1985) found that the growth rates of tilapia depends on to a
greater extent on the organization of the social hierarchy. The aggressive
behavior and competition for food and territory probably depressed the Rmax of
the mixed-gender group. The limited volume of water (as an environmental
condition) in our experimental tanks (10 - gallon) may have limited reproductive
behaviors and resulted in higher feed conversion ratios even though reproduction

was not observed in any of the tanks.

55

Metabolic rate could be another factor, which contributed to increased
growth response by male tilapia. Van Dam and Penning De Vries (1995)
observed that the metabolic rate of O. niloticus was 50% higher than the catfish
(Clan'as gan'epinus) because catfish were less aggressive. Hallerman et al.
(1986) suggested that different male and female allozymes physiologically
influenced the growth channel catfish (Ictalurus punctatus). This study agrees
with the observations of previous studies in that the male group growth rates
were higher, probably due to the higher potential metabolic rate, compared to the
females whether they were raised separately or in mixed-gender groups.

The amount of feed intake that produced half of the maximum growth

 

response (K0,!) in gram of feed / fish tank / six weeks for all the gender groups
were estimated. The optimum response is achieved with the highest possible
Rm response combined with the lowest possible Ko,5 value. Accordingly, with
consideration to the Rm value, the female-gender group used the highest
predicted consumption (the less efficient) estimated K0,; = 229.4 9. Whereas, the
male-gender group had the lowest significant estimated Ko_5 = 157.0 g with the
highest Rm value among the gender groups. In contrast, the mixed—gender
group had the lowest K“, = 132.3 g, and Rm... value (189.0 g) the lowest of the all

groups. The differences of K0,; between the groups could be an indicator for the

 

effects of the sex and metabolic rate on the feed uptake.
The predicted kinetic order for the response curve (n) was greater than

one, indicating a sigmoidal relationship. Differences in the n parameter value

56

reflect differences in the magnitude of response. The high n value is a result of
high Rmax response.

The predicted dietary responses of growth at zero feed intake level (b)
varied among the gender groups. The negative sign for this parameter for males
and mixed gender groups indicated fish were using nutrients from their bodies.
This parameter indicated the feed fed was insufficient to meet their basal
metabolic and daily activity requirements. The low b value obtained reflects the
high loss of fish body weight or nutrient. This parameter is directly related to the
Rm parameter. The highest (the best) predicted b value for the growth variable
was 6.3 g for the female-gender group. There was no significant difference for
the predicted b for both the male and the mixed-gender groups, which were -5.4
and -5.7 g, respectively. The high b value for the female-gender group probably
indicated that they have the highest feed efficiency to utilize their feed intake at
low feeding rate than the male whether separately or with the mixed-gender
group. Although, the female performed best at low feeding rates, males
performed better at higher feeding rates as demonstrated by differences
predicted in b versus Rm. Significantly, the feeding levels influenced the mean
final weight and feed conversion ratios (Siddiqui et al. 1997). This predicts that
the female—gender group had preformed growth better than the male at the low
feeding rates, while the male-gender group gained weight better than the female-
gender group at the high feeding rates. Simco et al. (1989) reported that the sex
of channel catfish (Ictalurus punctatus) did not influence the growth at a young

age, but sex had an increasing influence with increasing age.

57

The zero (0) line of response (maintenance level) was significantly
different for the growth response among the male and mixed-gender groups.
The optimum ML occurred at the minimum feed intake at 0 response. In other
words, the ML was the level of feed intake that met the daily activity requirement
without gaining or losing weight. The lower ML (the most efficient) for the growth
was predicted for the female-gender group. There was no predicted value for ML
for the female-gender group because the lowest feeding rate (0.5%) provided
sufficient feed to meet the ML requirements. This indicates the high efficiency of
the female-gender group to maintain their growth at low level of feeding
compared to the male separately or with the mixedvgender group. The ML of the
mixed-gender group was 26.9 g of feed per six week, which was approximately
0.5% of feeding rate. The ML for the male-gender group was 16.9 g of feed per
six week, which was approximately 0.3% of fish body weight per day. The
previous reasons could be involved increasing the ML for the males, whether

they were separate or mixed with the females in the mixed-gender group.

CRUDE PROTEIN

Although the predicted responses of crude protein between the gender
groups were not significantly different for the Rm, value, there were significant
differences in the K”. In this case, the male-gender group most efficiently
utilized protein compared to the other gender groups. The ratio of dietary protein
to energy is an important factor to promote growth efficiency and maximize feed

conversion (Garling and Wilson, 1976). Protein has also been shown to be a

$8

major source of energy for fish (Steffens, 1989). The male-gender group was
predicted to have the highest efficiency level of protein intake compared to the
other groups. Thus, the male-gender group consumed more protein, which could
be used as an energy source. The results of this study are in agreement with the
above studies.

The estimated response of b parameter of protein intake level was
significantly varied between the gender groups. The highest b parameter of
protein was 2.5 g for the mixed-gender group, followed by the female-gender
group (b = -1.1 g of protein) and the male-gender group (b = -1.6 Q). As
indicated above, the male-gender group had lower efficiency at the low feeding
rates (0.5 and 1.0%), where they used more protein than the other gender
groups for maintenance and daily activities. In the case of the mixed-gender
group, they did not loose protein from their bodies. Predicted data indicated that
the mixed-gender group gained some protein at low feeding rates during the
experiment.

The estimated ML of the protein requirements varied significantly among
the male and female-gender groups. The highest (worse) predicted protein
requirement for ML was 14.8 g of protein for the male-gender which was
predicted at 0.6% of feed per body weight of fish per day. Fish have been shown
to derive ATP mainly from protein when fasting or at low feeding levels (Love
1980). This is consistent with our observations of the response of the male-
gender group. The high ML value for the male-gender group may have been due

to the high requirement of protein that was not adequate to meet ML at low

59

feeding levels. The female group was more efficient than male group in using
protein at low intake levels (ML = 11.2 g, at 0.5% of feed per body weight of fish
per day). The mixed-gender group was the most efficient in protein utilization.
The ML = could not be predicted from the predicted growth response by

saturation kinetics model since it would have been less than 0.

CRUDE FAT

Fat has been shown to be a very important energy source for fish (Halver
1972). Typically, the total live weight fat content of tilapia has been between 5
and 6% (Balarin and Hatton 1979). In this study, there were significant
differences between the gender groups in the predicted fat deposition response.
The Rm, differences among the gender groups were significant. The highest
predicted Rm was 45.5 g of fat deposition per six week was observed for the
mixed-gender group. The estimated Rm for the male group was 36.9 g of fat
deposition. The lowest predicted Rm was 23.6 g of fat deposition for the
female-gender group.

The estimated K”, for fat deposition for all the gender groups were
significantly different. The highest estimated K0,; was 10.7 g of fat deposition for
the male-gender group which probably resulted from the high energy requirement
for basal metabolism and daily activities as indicated previously for the growth
and protein variables.

The b parameter is directly related to Rm... The lowest estimated b was —

1.8 g for the female-gender group and indicated that the female-gender group

had the lowest efficiency of crude fat utilization. The highest predicted b was -O.4
g of fat for the mixed-gender group. The predicted b for the male-gender group
was -O.8 g. This explains the high Rmax of fat deposition for the mixed-gender
and depression for the both the female and male-gender groups. Socially, the
aggressive behavior of males in the mixed-gender group may have caused the
females to use fat from their bodies as an energy source. The predicted fat level
for maintenance supports this assumption.

The highest predicted ML of crude fat requirement and fat deposition for
the mixed-gender group was 0.6 g, which was predicated at the 0.3% of feed per
fish weight per day. The ML for the male and the female-gender groups were 1.4
and 1.8 g for fat deposition, respectively, which are 0.7 and 1.0% of feed per fish
weight per day. This indicated that the female group had the highest fat
requirement (least efficient) to meet their daily needs compared to the other
gender groups. Females divert energy into egg production, which reduces the

amount of energy available for somatic growth (Mair et al. 1995).

TOTAL ASH

Unlike land animals, fish can meet part of their requirements for some
minerals, calcium for example, directly from the water through gill uptake
(Steffens 1989). Other minerals must be obtained by fish from their feed, such
as phosphorus (Halver 1972). Therefore, interpreting the total ash response for

fish can be difficult. The Saturation Kinetic Model predictions were based only on

61

the total ash levels provided by feed without consideration to minerals that may
have been provided by the hard water used in our experiments.

The predicted Rmax for total ash were significantly different among the
gender groups. The highest estimated Rmax for ash deposition was 40.3 g for the
male-gender group. Then the Rm“ for the female and the mixed-gender groups
were 36.5 and 27.6 g, respectively. The highest Rm, for the male-gender group
was probably due to their higher and faster potential metabolic rate of growth
compared to the other gender groups. The mixed-gender group had the lowest
estimated b (-1.3 g) and the lowest estimated Rm, (27.6 9) indicating that the
males may not have been responding at the same level compared to the male-
gender group. The estimated Ko.5 parameter for total ash also supports this
conclusion. The highest predicted K0,; for total ash was 29.5 g for the male-
gender group. This indicates that the male-gender group had the highest
demand for total ash for growth among the groups.

The highest prediction for b was -0.5 g of total ash for the female-gender
group because they had less demand than the male-gender group. The lowest b
was -1.3 g of total ash for the mixed-gender group because they gained the
lowest Rm, of total ash. In other words, they have lowest demand of growth due
to the genetic, social, and physiological factors between the male and the female
in the mixed-gender group. The highest predicted ML was 4.0 g for the female-
gender group. This indicates that the female-gender group has probably the
highest requirement for maintenance of total ash. Also, the high ML could be

used an indicator for the high demand of total ash for growth. On other hand,

62

this indicted that the male-gender group utilized total ash more efficiently and / or

retained more ash than the female group.

GROSS ENERGY

Steffens (1989) reported that energy .could be stored as protein or fat in
the fish body. The predicted energy deposition was significantly different among
all gender groups. The higher predicted gross energy response for the male
group was probably due to their capability of utilizing fat and protein compared to
the other gender groups. Feed consumption has been show to be regulated by
caloric intake (Lee and Putman 1973) which was supported by our observations
of Rm. Larger fish tend to a higher rate of energy consumption per unit gain
(Steffens 1989). The lowest predicted Rm response for gross energy was for
the mixed-gender group. This was probably due to the social competition
between males for females, which caused expended energy for defending
territories by the males in this group. Moreover, genetic and metabolic factors for
the females may have decreased the Rm of this group (Hallerman et al. 1986).
Observations of the Ko.s parameter support this assumption. The estimated K0,;
for deposited energy were significantly different for all the gender groups. The
highest (worse) K“, for the female-gender group. The K0,; for both the male and
the mixed-gender groups were not significantly different. The higher estimated
KM, value for the female-gender group indicated that they required higher feed

amounts to meet the half-maximum response.

63

At the zero (0) feed intake level, the predicted b for gross energy were
significantly different among all the gender groups. The estimated b of gross
energy for all the gender groups was positive indicating that the fish were able to
deposit energy even at the lowest feeding level (0.5%). The highest (best)
estimated b was 31.2 g for the mixed-gender group, which indicated that the
mixed-gender group extends the least energy. The b values for the cmde fat and
crude protein for the mixed-gender group were also the highest b values among
the gender groups. The lowest predicted b value was for the female-gender
group (b = 24.9 g), which was related to the low b value for both crude fat and
crude protein, the most essential energy sources, compared to the other groups.
Maintenance level predictions were not made for energy deposition for the
gender groups. The predicted ML for all the groups was greater than 0 which

means the actual ML was less than the lowest feeding rate (0.5%).

CONCLUSION

All-male Nile tilapia gender groups grow faster than female or mixed-
gender groups. The differences in growth can be explained by the saturation
kinetics curves generated during this study. Males exhibited higher Rmax and K05
for growth than female or mixed-gender groups because they used fat, protein
and energy more efficiently.

Based on our results, methods to provide all-male tilapia for aquaculture
should be used to maximize growth and performance.

The Saturation Kinetic Model is an easy tool to assess the nutritional
requirement for fish and other animals around the world and especially in the

developing countries.

65

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73

APPENDIX TABLES

Appendix Table 1. The dietary (intake) and fish (response) analysis for
growth of O. niloticus for the three groups.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Male Female Mixed gender
IFeeding Rate % Intake (9) Response (9) Intake (9) Response (9) Intake (9) Response (9)
0.05 27.8 3.5 23.8 6.5 28.5 1.0
0.05 25.6 3.0 22.6 8.0 27.9 2.0
0.05 25.3 2.0 22.3 9.0 29.4 0.0
1.0 55.4 12.0 43.5 10.0 40.5 13.0
1.0 57.0 13.0 58.3 5.0 62.9 32.0
1.0 53.4 16.0 54.0 15.0 59.2 34.0
2.0 117.9 82.0 106.3 45.0 73.9 59.5
2.0 129.4 74.0 104.2 58.5 125.2 131.0
2.0 144.9 108.0 99.1 58.0 131.7 93.5
4.0 237.2 146.0 266.6 99.5 244.4 140.0
4.0 248.4 182.5 290.6 105.0 294.0 126.5
4.0 299.0 136.5 269.6 107.5 319.2 125.5
6.0 530.5 188.5 491.0 169.0 461.6 169.0
6.0 518.7 209.5 476.3 172.5 405.7 170.0
6.0 499.1 217.0 475.0 187.0 429.7 178.5

 

 

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Appendix table 2. The dietary (intake) and fish (response) analysis for

protein of O. niloticus for the three groups.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Male Female Mixed gender
Feeding Rate % Intake (9) Response (9) Intake (9) Response (9) Intake (9) Response (9)
0.05 12.9 -1.6 11.0 -1.9 13.2 2.2
0.05 11.9 -1.2 10.5 -0.5 12.9 4.4
0.05 , 11.7 -0.9 10.34 0.4 13.6 4.8
1.0 25.7 2.0 20.2 1.5 18.8 5.1
1.0 26.4 1.0 27.0 1.3 29.1 9.3
1.0 24.7 6.5 24.9 3.6 27.4 10.7
2.0 54.6 14.6 49.2 11.9 34.2 11.8
2.0 59.9 7.5 48.2 13.3 58.0 30.2
2.0 67.1 19.9 45.9 13.1 61.0 21.5
4.0 109.8 26.9 123.4 23.3 113.2 31.6
4.0 115.0 33.5 134.6 24.3 136.1 30.3
4.0 138.5 19.9 124.8 25.9 147.8 31.2
6.0 245.6 36.6 227.3 39.7 213.7 43.7
6.0 240.2 48.2 220.5 42.4 187.9 34.9
6.0 230.6 45.0 219.9 49.8 198.9 45.5

 

 

 

 

 

 

 

 

 

75

Appendix table 3. The dietary (intake) and fish (response) analysis for fat of
O. niloticus for the three groups.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Male Female Mixed gender
Feeding Rate % Intake (9) Response (9) Intake (9) Response (9) Intake (9) Response (9)
0.05 1.1 -1.7 0.9 -1.5 1.1 0.01
0.05 1.0 -1.3 0.9 -1.9 1.1 -0.1
0.05 1.0 0.3 0.9 -1.7 1.1 -0.1
1.0 2.1 0.8 1.7 0.5 1.6 1.4
1.0 2.2 1.4 2.3 0.8 2.4 6.3
1.0 2.1 2.0 2.1 1.0 2.3 5.8
2.0 4.6 7.7 4.1 6.2 2.9 6.2
2.0 5.0 5.8 4.0 4.0 4.8 15.7
2.0 5.6 10.5 3.8 6.0 5.1 14.2
4.0 9.2 13.6 10.3 11.1 9.4 17.6
4.0 9.6 15.9 11.2 12.9 11.4 28.6
4.0 11.5 10.5 10.4 13.5 12.3 18.2
6.0 20.5 26.0 19.0 20.8 17.8 40.8
6.0 20.0 30.8 18.4 20.8 15.7 41.8
6.0 19.2 33.5 18.3 21.9 16.6 38.7

 

 

 

 

 

 

 

76

 

Appendix table 4. The dietary (intake) and fish (response) analysis for
ash of O. niloticus for the three groups.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Male Female Mixed gender
Feeding Rate% Intake (9) Response (9) Intake (9) Response (9) Intake (9) Response (9)
0.05 2.4 -0.9 2.0 -1.4 2.4 -0.6
0.05 2.2 -0.8 1.9 -1.0 2.4 -0.7
0.05 2.2 06 1.9 -0.9 2.5 -0.5
1.0 4.8 0.4 3.7 0.03 3.5 0.6
1.0 4.9 0.1 5.0 -0.5 5.4 2.6
1.0 4.6 1.4 4.6 0.4 5.1 2.6
2.0 10.1 7.1 9.1 3.1 6.3 5.6
2.0 11.1 3.8 8.9 5.4 10.7 9.6
2.0 12.4 7.6 8.5 6.4 11.3 15.0
4.0 20.3 12.4 22.8 12.7 21.0 13.6
4.0 21.3 17.1 24.9 12.0 25.2 14.4
4.0 25.6 11.2 23.1 13.4 27.4 15.7
6.0 45.5 24.2 42.1 24.6 39.6 25.3
6.0 44.5 37.9 40.8 28.9 34.8 23.4
6.0 42.7 20.4 40.7 33.6 36.8 24.0

 

 

 

 

 

 

 

77

 

Appendix table 5. The dietary (intake) and fish (response) analysis for

gross energy of O. niloticus for the three groups.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Male Female Mixed gender
Feeding Rate Intake Response Intake Response Intake Response
°/o (Kcal) (Kcal) (Kcal) (Kcal) (Kcal) (Kcal)
005 123.98 314.206 106.315 251,819 127,234 370,344
005 114,276 304.348 100.851 325,155 124,424 351.401
005 1 13,028 275,786 99.602 259.525 131,293 439,543
1 ,0 247,287 477,516 194,208 394,913 18—0.782 290,950
1 ,0 254.156 581,175 260,088 518,206 280,383 651,720
1 ,0 238,232 590,416 239,793 428,795 263,835 61 1,224
20 525,796 873,900 473,966 676,607 329,716 497,362
2.0 577,002 877,601 464.599 696.769 558.269 1 ,155.540
20 646,318 1 .028.315 442.119 634,615 587,618 946,145
40 1,057,838 1.110.456 1,188,974 1,037,963 1,090,310 1,139,686
40 1,107,794 1 .362.101 1,296,382 1,146,432 1,311,369 1,199,072
4.0 1,333,849 1,208,868 1 .202,713 1,088,405 1,423,772 1,201,901
60 2,366,084 1,641,277 2,189,986 1,628,441 2,058,849 1,539,204
60 2,313,629 1 .719,014 2,124,418 1,558,574 1,809,689 1,462,823
60 2,221,834 1,649,984 2,118,797 1,527,827 1 .916.472 1.598.685

 

 

 

 

 

 

 

78

 

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