substitution of fishmeal by soybean meal in diets for nile tilapia oreochromis niloticus a case study of rwanda

Substitution of fishmeal by soybean meal in diets for Nile tilapia Oreochromis niloticus: A Case study of Rwanda... Substitution of fishmeal by soybean meal in diets for Nile tilapia Ore

Substitution of fishmeal by soybean meal in diets for Nile

tilapia (Oreochromis niloticus): A Case study of Rwanda

Aloys MUSONI

Master thesis

July, 2014

Substitution of fishmeal by soybean meal in diets for Nile

tilapia (Oreochromis niloticus): A Case study of Rwanda

By Aloys MUSONI

June 2014

Dedication

To:

God, for his mercies and faithfulness

My wife Odette Mukanyandwi, my children Sedric Byiringiro and Sabrine Isimbi

Declaration

I hereby declare that this thesis has been produced by myself and is the result of my own investigations It has neither been accepted nor submitted for any other degree All sources of information have been accurately documented

Aloys MUSONI

Acknowledgements

First of all, I wish to express my appreciation to Almighty God for providing a safe environment and strength a long way my studies in Nha Trang University (Vietnam)

My sincere gratitude goes to Dr L A Tuan and Dr N V Minh for their advice,

guidance and technical support of this thesis

I wish to thank the Government of Rwanda which through PAIGELAC project provided funds for these studies Likewise, I would like to thank the Government of Vietnam through Nha Trang University for offering admission in master’s programme

I take this opportunity to express my gratitude to all staff of Nha Trang University for their help and creating a warm environment during my stay in Vietnam

Finally, I would like to extend a heartfelt thank you to all students of Nha Trang University for their moral support, kindness and friendship

Table of contents

Page

Dedication i

Declaration ii

Acknowledgements iii

Table of contents iv

Abstract vii

Abbreviation viii

List of tables ix

List of figures ix

Main parts of the thesis x

Introduction 1

Hypothesis and Research Objectives 3

Hypothesis 1 3

Objective 1 3

Hypothesis 2 3

Objective 2 3

Chapter 1: Literature review 4

1.1 World production and Aquaculture of tilapia 4

1.2 Tilapia Aquaculture in Africa 5

1.3 Status of Aquaculture in Rwanda 5

1.4 Perspective or potential of Aquaculture of Tilapia in Rwanda 6

1 5 Culture systems of Tilapia 8

1.5.1 Cage culture 8

1.5.2 Pond culture 8

1.5.3 Raceways systems 8

1.5.4 Recirculating Systems 9

1.6 Environmental factors of Tilapia 9

1.6.1 Temperature 9

1.6.2 Salinity 10

1.6.3 pH and Ammonia 10

1.6.4 Dissolved Oxygen 10

1.7 Nutrient requirements for tilapia 11

1.7.1 Energetics 11

1.7.2 Protein 12

1.7.3 Lipid 12

1.7.4 Carbohydrate 13

1.7.5 Vitamin and minerals 13

1.7.6 Amino acid profile 14

1.8 Tilapia feed characteristics and feeding behavior 15

1.9 Reproduction of tilapia 16

1.10 Digestibility of soybean meal 17

1.11 Limitation of using soybean meal in tilapia diets 18

1.11.1 Trypsin inhibitors 18

1.11.2 Phytic acid 18

1.11.3 Oligosaccharides 19

1.11.4 Saponins 19

1.12 Replacement of fishmeal with soybean meal in feed for Nile tilapia 19

Chapter 2: Material and Methods 21

2.1 Study area 21

2.1.1 Geography and Climate of Rwanda 21

2.1.2 Feeding trial at Kigembe Fish Farming Station 21

2.2 Experimental fish 22

2.3 Ingredients preparation and feed formulation 22

2.3.1 Protein analysis and procedure 23

2.3.2 Lipid analysis procedure 24

2.4 Feeding experiments 25

2.5 Growth parameters 26

2.6 Feed Conversion Ratio (FCR) 26

2.7 Statistical analysis 27

Chapter 3: Results and Discussion 28

3.1 Results 28

3.1.1 Water quality parameters 28

3.1.2 Growth, feed utilization (feed efficiency) and survival 28

3.1.3 Body crude protein (BCP) 31

3.2 Discussion 32

Chapter 4: Conclusion and Recommendations 35

4.1 Conclusion 35

4.2 Recommendations 35

References 36

Abstract

A feeding trial was conducted at Kigembe fish farming station to determine the effect

of fishmeal replacement in the formulated feed by soybean meal on growth, feed

efficiency and survival for fry Nile tilapia (Oreochromis niloticus) Five experimental

diets were formulated to be isonitrogenous approximately The diet 1 (control diet) included 100% of fishmeal (FM) while for the other diets fishmeal was partially replaced by soybean meal (diet 2, 75%FM & 25%SBM; diet 3, 50%FM & 50%SBM; diet 4, 25%FM & 75%SBM; diet 5, 0%FM & 100%SBM) The fry of Nile tilapia

(body weight 1.34 ± 0.025g) were sorted and stocked into 5 treatments with triplicate

groups for each treatment The experimental units were 15 hapas and all set up in one pond Feeding ration for each treatment was 10% of total fish biomass over the first 30 days which was divided and offered three times per day The amount was reduced up

to 8% of the total fish biomass for the next 30 days while 6% of total fish biomass was provided during the last 30 days The results produced showed that the Mean weight gain recorded for the fish fed with diet 2 (75%FM) and diet 3 (50%FM) were not significantly different from that of the fish fed with the control diet (P>0.05) Compared with the control diet, the results of specific growth rate (SGR) were statistically significant (P<0.05) for fish fed with the diet 5 (0%FM) while for the other diets (diet 2, 3 and 4) were not (P>0.05) The mean FCR recorded for the fish fed different amount of SBM did not show a significant difference (P>0.05) compared

to the mean FCR recorded for the fish fed the control diet The mean percentage survival of fish fed with different experimental diets did not show a significant difference (P>0.05) The results produced from body crude protein did not show a significant difference among treatment (P >0.05) The results showed that the total cost to prepare 1kg of feed was considerably reduced with increase in inclusion levels

of soybean meal in the diets The results proved that up to 50% of the SBM could be utilized by Tilapia safely and efficiently as alternative protein source in tilapia diets when the mean weight gain, specific growth rate, feed conversion ratio, survival and body crude protein are considered

Key words: Oreochromis niloticus, Tilapia feed, feed formulation, fishmeal

replacement, soybean protein alternative

AfDB: Africa Development Bank

AOAC: Association of Official Analytical Chemists

CGM: corn gluten meal

EAA: essential amino acids

FAO: Food and Agriculture Organization of the United Nations

FCR: feed conversion ratio

FFSB: full-fat soybean

FM: fish meal

IFFO: international fishmeal and fish oil organization

MINAGRI: Ministry of Agriculture and Animal Resources

MT: million metric tons (MT)

PAIGELAC: Inland Lakes Integrated Development and Management Support Project PER: protein efficiency ratio

PPV: protein production value

RAB: Rwanda Agriculture Board

SBM: soybean meal

SGR: Specific Growth Rate

USAID: United States Agency for International Development

List of tables

Page

Table 1.1: Limits and optima of water quality parameters for tilapia 11 Table 2.1: Ingredients used for experimental diets (1,000g) 23 Table 2.2: Proximate composition of dietary ingredients used in experimental diets fed

to tilapia fry 24 Table 2.3: The proximate composition of protein and lipid in each experimental diet 25 Table 3 1: Water quality parameters recorded during the experimental period 28 Table 3.2: Growth performance of fry Nile tilapia fed with experimental diets

containing Variable amounts of soybean meal in period of 3 months 29 Table 3.3: The crude protein percentages of Tilapia fish fed different experimental diets and total cost to prepare 1 kg of each experimental diet considering the price of each ingredient 32

List of figures

Page

Figure 3.1: Effect of dietary fishmeal replacement with soybean meal on the Mean Weight Gain of Fry Nile tilapia 30 Figure 3.2: Total number of fish for different treatments during the experimental period of 3 months 31

Main parts of the thesis

Chapter one of the present thesis includes a review of literature Chapter two describes the methodology used in this research thesis Chapter three presents and discusses the results obtained Finally, Chapter four provides conclusion and recommendations

Introduction

Tilapia are known as ‘‘aquatic chicken’’ because of their fast growth, good quality flesh, disease resistance, adaptability to a wide range of environmental conditions, ability to grow and reproduce in captivity, and feed on low trophic levels Therefore, they have become an excellent choice for aquaculture, especially in tropical and subtropical environments [1]

A major determinant of successful growth and intensification of aquaculture production depends on aquafeed Feed is the single largest operating expense (30-70%) in all types of intensive aquaculture farming [2]

The development of commercial aquafeeds has been traditionally based on fishmeal as the main protein source due to its high protein content and balanced amino acid profile Fishmeal has the right combination of essential amino acids, fatty acids, vitamins and minerals for fish growth [3]

Fishmeal has been the most expensive one among the ingredients used for feed formulation Fish made into fish meal are caught from the wild The shortage in global fishmeal production coupled with increased demand and competition for its use in livestock and poultry feeds has further increased fishmeal prices [3]

Therefore, replacement of fishmeal with alternative proteins with sustainable supplier

or less expensive would be beneficial in reducing feed costs Soybean meals widely used as the most cost effective alternative for fishmeal in feeds formulated for many fish species employed in aquaculture [4] Proteins from soybean are widely available, and economical with relatively high digestibility and energy contents [5]

The problem facing with in aquaculture industry is to reduce the inclusion rate of fishmeal in aquafeeds and show the economical importance and environmental friendly of replacing fishmeal in aquafeeds by less expensive plant protein source [6]

Soy protein concentrate (SPC) supplemented with L-methionine totally replaced fish meal in low-fat diets without affecting nutrient utilization of rainbow trout [7] Goda

et al [8], comparatively studied growth performance of Nile tilapia and tilapia galilae

(Sarotherodon galilaeus, Linnaeus, 1758) fed on fishmeal free diets (100% fishmeal

replacement) They found that growth performance of Nile tilapia were reduced when replaced fishmeal by soybean meal (SBM), full-fat soybean (FFSB) or corn gluten meal (CGM) under ideal protein profile The reduction of growth performance and feed utilization was observed when the high levels (> 10%) of FFSB were

incorporated in fish diets However, tilapia galilae (Sarotherodon galilaeus, Linnaeus,

1758) can well accept SBM and CGM diets; so much as fish fed SBM diet showed higher Specific Growth Rate (SGR) and lower feed conversion ratio (FCR) than those

of fish meal (FM) group

Most of the above studies have been conducted within closed indoor rearing systems (i.e Fish usually being reared within small artificial rearing tanks or aquaria within a water recirculation system) It was therefore more important to conduct this study for

Nile tilapia (Oreochromis niloticus) in the same manner of fish farmers (in outdoor

Hypothesis and Research Objectives

Hypothesis 2

Completed replacement of fishmeal with soybean meal as source of protein for Nile

tilapia is not acceptable due to its detrimental effects on fish

Chapter 1: Literature review

1.1 World production and Aquaculture of tilapia

Aquaculture continues to grow rapidly than any other animal-producing sectors, with

an annual growth rate for the world of 8.8 percent since 1970, compared with only 1.2 percent for capture fisheries and 2.8 percent for terrestrial farmed meat production systems over the same period [9]

The annual global total production of tilapia was less than 500,000 metric tons in the early 1990s and reached 3.5 and 3.59 million metric tons in 2011 and 2012 respectively In 2013 it was forecasted to climb 3.4 percent while in this year it should approach around 3.9 million metric tons [10] These observations indicate a significant increment of tilapia production in the world Most of the production came from extensive /semi-intensive systems in developing countries, particularly in Asia [11]

Tilapia is the second most important culture freshwater finfish in the world after the carps Currently, farmed tilapia represents more than 75% of world tilapia production [11], and this contribution has been exponentially growing in recent years Tilapia plays an important role in food security and poverty alleviation in the developing countries such as Indonesia, the Philippines, Thailand and China [12] Several factors have contributed to the rapid global growth of tilapia, such as cultured simple technique and good adaptation to a wide range of environmental conditions

Tilapia is one of the most important omnivorous fish species reared in aquaculture systems They are widely cultured in tropical and subtropical regions of the world

such as Egypt, Taiwan and Senegal There are three genera of tilapia; Oreochromis, Sarotherodon and Tilapia The primary genus reared for aquaculture is Oreochromis which includes Nile Tilapia (O niloticus), Mozambique Tilapia (O mossambicus), and Blue Tilapia (O aureus and O urolepis hornorum) [13]

Tilapia found in the family of Cichlidae, is well adapted to enclosed water The tilapia

is an omnivorous species that uses a wide spectrum of foods [14], efficiently uses dietary carbohydrates and has a great ability to digest plant protein [15]

1.2 Tilapia Aquaculture in Africa

Although Tilapia species are native from Africa and the Middle East, Food insecurity remains a serious problem in the developing world, particularly in Africa This is due

to the low existing biotechnical, economic and institutional challenges, which include lack of national policies to guide aquaculture development, unfriendly investment policies, the absence of linkages between farmers, research/technology development and extensions, and unfavorable investment climates [16]

Fortunately, there have been many attempts to promote aquaculture as a means to address poverty and food insecurity in Africa, although with limited success The outlook in North Africa differs from that of sub-Saharan Africa and the Near East largely due to the impact Egypt has in the region, almost half of total tilapia production in Africa came from Egypt [17] The farmers in this country operate on 1

to 2 ha earthen ponds, producing primarily O niloticus

Although there are no projections for North Africa or the Near East [18], in his review

of Egypt and in his regional review of North Africa and the Near East predicted continued and sustained growth of tilapia aquaculture in those regions

1.3 Status of Aquaculture in Rwanda

As a landlocked country, Rwanda’s aquaculture relies on its rich fresh water resources About 8% of the area is covered by water (210,000 ha), of which lakes occupy 128,000 ha The country’s lakes are the main source of fish production Principally, Rwanda has a large potential for aquaculture Besides pond aquaculture in watershed areas with sufficient water availability, the needed site conditions for cage aquaculture are given in various lakes [19]

Until recently Rwanda has been more or less self-sufficient as regards food supplies However, the estimated population increase is greater than the rate of increase of food

production Thus, the Government of Rwanda is taking various steps to stimulate domestic food production, including strategic measures aimed to increase the production of fish from the numerous subsistence-level ponds operated by small groups of farmers throughout capture fisheries in lakes and aquaculture in ponds [19]

1.4 Perspective or potential of Aquaculture of Tilapia in Rwanda

Although, aquaculture in Rwanda had been introduced in 1949 by the Belgium colonial, it has been promoted in 1983 by the National Fish Culture Project This project was bilaterally funded by the United States Agency for International development (USAID) and the government of Rwanda It continued through 1988 and then reduced funding for a second phase that was part of a Natural Resources Management Project Other several previous fish culture projects had been operating

in Rwanda, including two that were funded by the Food and Agriculture Organization

of the United Nations (FAO) and one that was funded by the government of Canada, but none of these projects demonstrated success due to the absence of linkages between, research/technology development and extensions services [20]

Thereafter, the aquaculture in Rwanda has slowed down slightly between 1990 and

2004 may be due to the political issues [21] After that period, the Inland Lakes Integrated Development and Management Support Project (PAIGELAC), was conceived in 2004 after when the government of Rwanda realized that inland water bodies were degenerating The capture fisheries were dwindling, the massive erosion was silting the lakes and overfishing had reached hazardous levels The ultimate goals were to increase fish production, improve nutrition, ensure food security and improve the incomes of the beneficiaries in a sustainable manner [21] The project was funded

by the Africa Development Bank (AfDB) Initially, PAIGELAC project objectives were focused on only fisheries development, management of inland lakes and water sheds protection

According to the Master plan (2011), the target production from fish farming (in both intensive pond and cage culture) around 112,000 MT by 2020

In order to attain the objective, the Government of Rwanda through the PAIGELAC project, a total of 15 lakes with a surface area of 15,380ha restocked with 381,113 (in

each lake) of Tilapia niloticus fingerlings However, at Midterm review it was realized

that capture fisheries only could not be sufficient to provide enough fish to the growing Rwandan population It was therefore recommended that the project extends its activities in aquaculture development [19]

The low production from capture fisheries was estimated at 17,158 MT while the statistical data from aquaculture sector were not considered due to the insignificant production of the sector [11] Due to the gap presented, the Government also invested

a lot of money in aquaculture by creating new ponds and rehabilitating the old ones as sponsorship for fish farmers working as cooperatives The project has rehabilitated

nearly 218 ha of fish ponds and had also stocked with Nile tilapia (Orechromis niloticus) in May 2012 It was in this context that Kigembe Fish Farm was also

rehabilitated and expanded to become a modern tilapia fish hatchery center The center was supplied with fresh brood stock (Nile tilapia) from Lake Albert and some form of selective breeding has also begun so as to ensure supply of good seed in future The hatchery has a capacity of producing up to 10 million fingerlings every year The project introduced also the cage culture techniques in lakes A total of 678 cages with volume ranged between 8m3 to 27m3 were installed in Lake Bulera, Ruhondo, Kivu and Muhazi for Tilapia intensive farming [22]

The main species cultured in Rwanda is Tilapia nilotica (Oreochromis niloticus) Common carp are also raised in ponds, but on a very small scale Tilapia macrochir and T rendalli are not fast growing species and experience elsewhere in Africa suggests that growth rates of Tilapia macrochir and T rendalli are generally only 0.5

g/day and never exceed 1 g/day, even with fertilization of the ponds and artificial

feeding [23] Clarias carsonii occurs sometimes in ponds, but are not appreciated by

population

One of the main bottlenecks in development of aquaculture in Rwanda is the all-year round availability of fingerlings of suitable fast growing species for pond culture At

present only fingerlings of Tilapia nilotica (Oreochromis niloticus) are recommended

and available at the Kigembe Fish Farming Station

1 5 Culture systems of Tilapia

Tilapia can be raised under a number of different culture systems including cages, ponds, raceways, closed and semi-closed indoor recirculating systems While each culture system is unique and has many advantages and disadvantages, they all share the common goal of efficient production [24]

1.5.1 Cage culture

The cages are used in circumstances where fish cannot be controlled without human interaction Lakes, streams, and reservoirs often require fish to be enclosed with wire fabric or nylon netting which is attached to a rigid frame that may be suspended to a floating platform or flotation devices [24] Generally, good water quality is achieved

in cage systems which allow for higher stocking rates The startup costs, maintenance, and replacement costs of cages can be quite high [24] As well, it is difficult to control diseases, and production may be lost due to net damage

1.5.2 Pond culture

The Ponds are used by small culturists and researchers because they are easy to maintain and have low costs associated with them [24] Production levels are directly related to pond design including side slopes, drain structure and inflow lines, which are needed to ensure adequate water levels at all times, provide proper drainage and prevent vegetation growth within the pond [24]

1.5.3 Raceways systems

The production of tilapia in raceways, an enclosed channel system, is very efficient Raceways can accommodate extremely high densities of fish which can be maintained due to the high rates of water flow (from gravity) resulting in exceptional water quality [24]

1.5.4 Recirculating Systems

The systems known as recirculating systems, allow water to circulate within a number

of culture tanks passed through a settling column to remove solids, and a biofilter to detoxify the ammonia produced by fish [24] Recirculating systems can also be a semi-closed system where small amounts of water are removed and replaced with fresh water Closed or semi-closed systems are beneficial for production of tilapia species in countries that do not have warm year-round climates or have a shortage of fresh water or available land [25] Recirculating systems designs are based on cost-effective water treatment Culturing tilapia in recirculating systems has a number of disadvantages Complete diets must be formulated and a feeding system implemented using either hand or a mechanical feeder Depending on the type of system, pollution

of surrounding water or land with nutrients and organic matter may arise from water and waste discharge [26] Pumps, aerators, filters, CO2 and heaters can be costly and need constant maintenance [26] Finally, with high stocking densities, fish are subjected to increased stress which may result in disease outbreaks [26]

1.6 Environmental factors of Tilapia

This group of warm water, omnivorous species cultured throughout the world and comprising a large portion of global production is various tilapia species

(Oreochromis and Tilapia sp.) These fish are native to Africa and the Middle East,

but have been cultured in tropical and temperate regions around the world The Nile tilapia will reportedly thrive in any aquatic habitat except for torrential river systems and the major factors limiting its distribution are salinity and temperature [27] Tilapia can also tolerate dissolved oxygen, pH, and ammonia levels than most cultured freshwater fishes can [1]

1.6.1 Temperature

Temperature is a major metabolic modifier for Tilapia fish Optimal growing temperatures are typically between 22°C (72° F) and 29°C (84°F); spawning normally occurs at temperatures greater than 22°C (72°F) Most tilapia species are unable to survive at temperatures below 10°C (50°F), and growth is poor below 20°C [28]

Oreochromis niloticus is described as having a high tolerance for a range of

temperatures, with a lower lethal limit of 8ºC and an upper limit of 42ºC Temperature tolerance not only depends on each species, but it also depends on the size of the individual Young fish, which are smaller in size than adults, are typically more tolerant of high and low temperatures [29]

1.6.2 Salinity

In general, most tilapias are highly tolerant of saline waters, although salinity tolerance differs among species Nile tilapia is thought to be the least adaptable to noticeable changes (direct transfer, 18 parts per thousand in salinity); Mozambique,

blue, and redbelly (T zilli) are the most salt tolerant With the exception of Nile

tilapia, other tilapia species can grow and reproduce at salinity concentrations of up to

36 parts per thousand, but optimal performance measures (reproduction and growth) are attained at salinities up to 19 parts per thousand [1]

1.6.3 pH and Ammonia

Other water quality characteristics relevant to tilapia culture are pH and ammonia In general, tilapia can tolerate a pH range of 3.7 to 11, but best growth rates are achieved between pH 7 to 9 [30] Ammonia is toxic to tilapia at concentrations of 2.5 and 7.1 mg/L as unionized ammonia, respectively, for blue and Nile tilapia, and depresses feed intake and growth at concentrations as below as 0.1 mg/L Optimum concentrations are estimated to be below 0.05 mg/L [31]

1.6.4 Dissolved Oxygen

Tilapia are, in general, highly tolerant of low dissolved oxygen concentration, even down to 0.1 mg/L [32], but optimum Tilapia growth is obtained at concentrations greater than 3 mg/L [30] The following table summarizes the range and optimum for growth of Nile tilapia

Table 1.1: Limits and optima of water quality parameters for tilapia

1.7 Nutrient requirements for tilapia

The low trophic level and the omnivorous food habits of tilapia make them a relatively inexpensive fish to feed, unlike other finfish, such as salmon, which rely on high protein and lipid diets based on more expensive protein sources like fish meal In

addition, tilapia are similar to channel catfish (Ictalurus punctatus), in that they can

tolerate higher dietary fiber and carbohydrate concentrations than most other cultured fish To ensure high yield and fast growth at least cost, a well-balanced prepared feed

is essential to successful tilapia culture [33]

1.7.1 Energetics

Energy is not a nutrient but is a property of nutrients that are released during the metabolic oxidation of proteins, carbohydrates and lipids Available data on energy requirements of tilapias have been reported in terms of gross energy (GE), digestible energy (DE) or metabolizable energy (ME) in relation to the dietary level of protein

[33] As the digestible energy (DE) content in the diet increased, consumption by O niloticus decreased, but the amount of protein in the diet did not affect consumption

[34]

Energy needed for fish is significantly different than in mammals and birds This is due to 2 factors: 1) fish are poikilothermic and 2) energy expenditure to produce urea

or uric acid is avoided because fish excrete ammonia directly through their gills [35]

In terrestrial livestock, the energy losses due to the heat increment can be 20-30% of the intake energy [36] while for fish this is only 5-15% of intake energy [37] Furthermore, the maintenance energy requirements of fish are only 5-10% of those for similar sized terrestrial livestock [38] These differences mean that fish are significantly more efficient in converting feed into body tissues than terrestrial species

if an optimal environment is provided

1.7.2 Protein

Protein is responsible for a large part of the cost of most prepared diets Generally, protein is given the first priority in formulating fish diets because it is the most expensive component of the prepared diets [39] The protein requirement of tilapia decreases with age and size, with higher dietary CP concentrations required for fry (30–56%) and fingerlings (30–40%) tilapia but lower protein levels (28–30%) for larger tilapia [40]

1.7.3 Lipid

Dietary lipids provide a major source of energy, facilitate the absorption of fat soluble vitamins, play an important role in membrane structure and function, serve as precursors for steroid hormones and prostaglandins, and serve as metabolizable sources of essential fatty acids needed by fish for normal growth and development [41] Protein – sparing effects of non-protein nutrients such as lipids is necessary and should be used to reduce diet costs and maximize nitrogen retention Lipids, especially phospholipids, are important for cellular structure and maintenance of membrane flexibility and permeability [42] Studies on T Zillii [43] indicated that increasing dietary lipid up to 15% resulted in a significant improvement in protein efficiency ratio (PER) and protein production value (PPV) Dietary lipids have been shown to have a sparing effect on the utilization of dietary protein The level of protein in the

diet of O niloticus can be reduced from 33.2% to 25.7% by increasing dietary lipid

from 5.7% to 9.4% and carbohydrate from 31.9% to 36.9% [42] A right amount of fat

can improve taste and texture but excessive fat may pose a health hazard to fish The amount of 5% dietary lipid appeared to be sufficient to meet the minimal requirement

of juvenile tilapia, but a level of 12% was needed for maximal growth [44] Similarly, Jauncey [39], suggested that to maximize protein utilization, dietary fat concentration should be between 8 and 12% for tilapia up to 25 g, and 6 to 8% for larger fish

1.7.4 Carbohydrate

Carbohydrates are the least expensive form of dietary energy for human and domestic animals, but their utilization by fish varies and remains somewhat obscure It provides energy but most of them are not easily digested by ordinary carnivorous marine species such as grouper, red snapper and mangrove snapper Fish in general utilizes dietary carbohydrate poorly No dietary requirement of carbohydrate has been demonstrated in fish It has been reported that the utilization of starch was significantly higher than that of glucose for tilapia It has also been reported that tilapia utilizes disaccharides better than glucose but more poorly than starch [45] Carbohydrates provide a relatively inexpensive source of energy compared to protein, and their inclusion can improve the quality of pelleted feeds Tilapia can effectively utilize carbohydrate levels up to 30 to 40% in the diet, which is considerably more than most cultured fish [46] Fiber is usually considered indigestible, as tilapia does not possess the required enzymes for fiber digestion (although some cellulase activity

from microbes has been found in the gut of O mossambicus [47] For this reason, and

to attain maximum growth, crude fiber levels in tilapia diets should probably not exceed 5% [46]

1.7.5 Vitamin and minerals

Vitamins are organic substances that are essential for growth, health, reproduction and maintenance in animals, but required in small amounts Since fish cannot synthesize vitamins at all or can only synthesize in insufficient quantity for normal development, growth and maintenance, they must be supplied in the diet Other than the 13 known vitamins, i.e thiamin, riboflavin, niacin, pantothenic acid, biotic, folic acid, vitamin B6, B12, C, A, D, E, and K their requirements have been quantified for tilapia [48]

Basic knowledge of mineral toxicity and interactions among minerals is necessary when supplementation is made Though not specific to tilapia, excessive supplies of certain minerals can cause deficiencies of others and in extreme cases toxicity to fish For example, high dietary calcium can cause deficiencies in phosphorus, zinc, iron, and manganese On the other hand, it has been shown that zinc, copper, and selenium,

at high concentrations, can be toxic to various finfish species Vitamins and minerals are the essential trace elements that can enhance natural resistance and feed conversion rate [48]

1.7.6 Amino acid profile

In general, Tilapias require the same ten essential amino acids (arginine, histidine, isoleucine, leucine, lysine, phenylalanine, methionine, threonine, tryptophane, and valine) as the other fish and terrestrial animals [49]

The supplementation of these EAA into the diets has been a common practice in tilapia diet However, it was found that the utilization of many protein sources in tilapia feeds may be limited by dietary minerals (such as phosphorus and zinc), rather than the deficient EAA This means that the inclusion of dietary EAA may not be necessary if the diet contains proper levels of certain minerals For example, the inclusion of dietary phosphorus source to SBM-based diet may meet the requirement for deficient EAA (Methionine) The non inclusion of the deficient EAA to SBM-based diet did not result in any growth retardation, while SBM supplemented with 3% dicalcium phosphate (DCP) and oil completely replaced FM without any adverse effects on fish growth [50] The non-necessity of EAA supplementation has also been reported with sesame seeds [51] Sesame seeds are deficient in Lys and zinc The supplementation of either Lys or zinc significantly improved the growth and survival

of T zillii [51] Once again, Lys or zinc may meet the requirement of one another,

supporting the argument that certain minerals rather than EAA deficiency may be the limiting factor in sesame seeds Adopting this approach, it may improve the protein quality and reduce the cost of the diets

1.8 Tilapia feed characteristics and feeding behavior

Feed is available in a variety of sizes ranging from fine crumbles for small fish to large (1/2 inch or larger) pellets Tilapia generally feed on slow sinking pellets, but they will also consume feed that has fallen to the bottom of the culture tank [52] The pellet size should be approximately 20-30% of the size of the fish species mouth gape Feeding too small a pellet results in inefficient feeding because more energy is used in finding and eating more pellets Conversely, pellets that are too large will depress feeding and, in the extreme, cause choking Select the largest sized feed the fish will actively eat Commercial fish diets are manufactured as either extruded (floating or buoyant) or pressure-pelleted (sinking) feeds Both floating and sinking feed can produce satisfactory growth, but some fish species prefer floating, others sinking Shrimp, for example, will not accept a floating feed, but most fish species can be trained to accept a floating pellet [52]

Tilapias are naturally habituated to eating plant ingredients, and are typically

considered strict herbivores once they reach maturity [53] Nile tilapia (Oreochromis niloticus) has considerable potential for aquaculture in many tropical and subtropical

regions of the world These species typically do not exhibit reduced acceptability of prepared diets containing plant feedstuffs and are generally less dependent on fish meal and other protein feedstuffs of animal origin compared to carnivorous species Tilapia feed on a wide variety of dietary sources, including phytoplankton, zooplanktons, larval fish, and detritus [54]

Adult tilapias are principally herbivorous but readily adapt to complete commercial diets based on plant and animal protein sources Therefore, the ability to substitute soybean meal for fish meal in diet formulations for these species is significant [55]

Floating feed (Dry feed) and Sinking feed (moisture feed)

The dry type process of pellet feed can eliminate most bacteria Dry pellet feed does not decay easily because it is very low in moisture content (about 10%) Extruded feeds are more expensive due to the higher manufacturing costs Usually, it is

advantageous to feed a floating (extruded) feed, because the farmer can directly observe the feeding intensity of his fish and adjust feeding rates accordingly The moisture content of moist pellet feed is about 35% but the trash fish added makes it rot more easily Refrigeration is therefore essential Determining whether feeding rates are too low or too high is important in maximizing fish growth and feed use efficiency [35]

1.9 Reproduction of tilapia

Tilapia species (Oreochromis niloticus) are the species that exhibit a high degree of

Parental care Parental care is a rare feature in most fish, but is a successful reproductive strategy in fish of the Cichlidae family of tilapia The importance of parental care is to increase fitness by supporting growth and development of the young and providing protection from predators Parental care is provided predominantly by the maternal side [53]

Oreochromis niloticus species are maternal mouth brooders, the male selects an

appropriate mating site to dig a nest, on the shallow of water body [56] With a little luck, the male attracts a ripe female with courtship displays who lays eggs in the nest She then picks up the eggs in her mouth and finds a safe zone while the male is fertilizing them The males will continue to court other females, while the female that has just spawned retreats away from the nest to incubate the eggs Males play no part

in parental care and can mate with many females at a time; therefore sex ratios in breeding ponds can be as high as seven females to one male

The eggs hatch in the mouth of the female after about five to seven days (depending

on water temperature) and the hatchlings remain in the mouth while they absorb their yolk sacs [53] Tilapia fry start swimming out of the mouth to feed but return back to the mouth of the female at any sign of danger Once the fry have become too large to fit in the females’ mouth they become totally independent and move to warm, sheltered water such as near the edge of a pond The number of eggs a female will produce is dependent on body size This can range from 100 eggs (produced by a 100g