Evaluation of replacing fish meal with corn protein concentrate in Nile tilapia Oreochromis niloticus fingerlings commercial diet

Four isocaloric‐isonitrogenous diets containing 0, 50, 100 and 190 g/kg corn protein concentrate (CPC) as replacement for dietary fish meal were fed to Nile tilapia Oreochromis niloticus fingerlings for 8 weeks. Tilapia growth parameters were not significantly (p > .05) different in fish fed diets with 0, 50 and 100 g/kg CPC and found to be superior compared to those fed on 190 g/kg CPC. Fish dressing ratios and body composition were similar among all treatments. The electron microscope indicated that the stomach size of control fish was slightly smaller and the wall was thinner while the stomach of the fish fed all other levels of CPC undergone a remarkable size increase and their walls were thicker after feeding diets with CPC. Total aerobic bacterial and coliform counts were significantly decreased in fish intestine when fed diets with 100 and 190 g/kg CPC compared with fish fed diets with 0 g/kg or 50 g/kg CPC. This study indicates that it is possible to replace up to 534 g/kg of dietary fish meal in tilapia fingerlings using 100 g/kg of CPC without any negative effect on fish growth and proximate body composition.     

Effect of using okara meal,a by‐product from soymilk production as a dietary protein source for Nile tilapia (Oreochromis niloticus L.) mono‐sex males

The main objectives of this study was to evaluate the effect of partial and total replacement of fishmeal protein by okara meal (OM) protein in practical diets on growth performance, feed utilization and body composition of Nile tilapia (Oreochromis niloticus L.) mono‐sex males. Fish of an average initial weight of 2.67 ± 0.01 g were stocked in 15 glass aquariums (80 L each) at a rate of 15 fish per aquarium. Fishmeal protein (18% of the diet) was used as the sole source of animal protein in the control diet. Percent replacement of fish meal (FM) by OM on the basis of crude protein was as follows: 0% (control diet A), 25% (diet B), 50% (diet C), 75% (diet D) and 100% (diet E). Diets were fed to fish at a rate of 5%, and then gradually reduced to 4% of the total fish biomass daily, for a period of 12 weeks. The results revealed that the fish fed diets A (100% FM control), B (25% OM), C (50% OM) and D (75% OM) had significantly the best average body weight, weight gain g, specific growth rate (SGR % day^?1), weight gain % and feed intake g fish^?1 compared with diet E (100% OM) which had the lowest values. There were no significant differences (P > 0.05) among all experimental diets and control in terms of feed conversion ratio (FCR), protein efficiency ratio (PER) and survival rate %. Whole body protein contents for fish fed diets B, C and D were superior to the control diet. Incorporation of OM in the diets increased significantly whole body fat content. Incorporation of OM in the diets significantly increased apparent digestibility coefficient of crude protein crude fat and energy. Therefore, these findings suggest that up to 75% of FM protein can be replaced by OM protein in Nile tilapia, mono‐sex male diets.     

Replacement of fish meal with a mixture of different plant protein sources in juvenile Nile tilapia, Oreochromis niloticus (L.) diets

A plant protein mixture (PPM) was tested to replace fish meal (FM) in diets for juvenile Nile tilapia, Oreochromis niloticus. Fish averaging (±SD) 3.7±0.14 g were divided into 15 groups. Three groups were fed each of five isonitrogenous (33.6%) and isocaloric (4.7 kcal g^?1) diets replacing 0%, 25%, 50%, 75% and 100% of the FM protein with similar percentages of PPM (PPM0, PPM25, PPM50, PPM75 or PPM100 respectively). The PPM consisted of 25% soybean meal, 25% cottonseed meal, 25% sunflower meal and 25% linseed meal, and 0.5% of both methionine and lysine were added to each diet except for the control. After 16 weeks of feeding, the fish fed diets PPM75 and PPM100 exhibited growth performance not differing significantly from the fish fed control diet. PPM substitution of up to 75% of the FM protein did not result in differences in the apparent protein digestibility compared with the control, whereas in the PPM100 group digestibility was significantly lower than in the other groups, except for fish fed the PPM75 diet. The incorporation of PPM in diets did not significantly affect whole‐body dry matter, protein, fat or energy compared with the control. The cost–benefit analyses of the test diets indicated that the PPM diets were economically superior to FM. The protein from PPM can completely replace the FM protein in the diets for Nile tilapia, based on the results of this study.     

Use of cottonseed meal supplemented with iron for detoxification of gossypol as a total replacement of fish meal in Nile tilapia, Oreochromis niloticus (L.) diets

The objective of this study was to determine the effect of total replacement of fish meal by cottonseed meal (CSM) supplemented with various levels of iron in practical diets on growth performance, feed utilization, body composition and some biological and haematological parameters of Nile tilapia, Oreochromis niloticus (L.). Juvenile fish (average weight 3.78±0.1 g) were stocked in 18 glass aquariums (80 L each) at 25 fish per aquarium. Fish meal (50% of the diet) was used as the sole source of animal protein in the control diet 1. Diets 2–6 had 100% CSM (0.145% free gossypol) protein with various levels of supplemented iron (86, 486, 972, 1458 and 1944 mg Fe kg diet^?1) in diets 2–6 respectively. Diets were fed to fish twice daily at a rate of 3% of body weight during the first 12 weeks then 2% of the total fish biomass daily until the end of the experiment (30 weeks). The results of this study revealed that, groups of fish fed diets 1, 4, 5 and 6 had significantly (P≤0.01) the higher average body weight and specific growth rate than those of fish fed diet 2 (100% CSM without iron supplementation) and diet 3 (100% CSM plus 486 mg Fe kg diet^?1). The best values for feed conversion ratio, protein efficiency ratio and condition factor (K) were recorded with groups of fish fed diet 4 (100% CSM plus 972 mg Fe kg diet^?1). Red blood cell count, haematocrit and haemoglobin were increased with increasing levels of iron and significantly affected by dietary iron. Hepatosomatic index for diets 3–6 were not significantly different (P>0.05) and superior to that of diet 1 control [100% fish meal (FM)]. The gonadosomatic index of males of Nile tilapia was not influenced by CSM diets with or without iron, while females of Nile tilapia were significantly influenced with iron and the lowest values were recorded with groups of fish fed diet 2 (100% CSM without iron supplementation). Apparent digestibility coefficients of protein, fat dry matter and energy were relatively high for most diets supplemented with iron and increased by increasing iron supplementation. There were no significant differences between groups of fish fed diet 1 (100% FM) and diets 5 and 6 which contained 100% CSM with additional 1458 and 1944 mg Fe kg diet supplemental iron^?1 respectively. Proximate composition of whole body was not influenced by diet. Adding 972 mg Fe kg diet^?1 from ferrous sulphate to the CSM‐based diets that contained 972 mg free gossypol (1:1 iron to free gossypol ratio) for Nile tilapia reduce the negative effects of gossypol and improved growth performance, feed utilization and blood parameters and can totally replace fish meal in tilapia diets.     

Partial replacement of soybean meal by sesame meal in diets of juvenile Nile tilapia,Oreochromis niloticus L.

An 8‐week feeding trial was conducted to determine the effects of replacing of soybean meal (SBM) with sesame meal (SM) in the diets of Oreochromis niloticus fingerlings. Seven practical diets (33 g kg^?1 crude protein, 19.2 MJ kg^?1 dry diet) containing substitution levels of 0%, 8%, 16%, 24%, 32%, 40% and 48% SM for SBM protein were formulated and fed to triplicate groups of O. niloticus fingerlings (mean initial weight of 8.74 ± 0.12 g). The fish survival rate, hepatosomatic index, viscerosomatic index and condition factor were not significantly affected by the contents of SM in the diets (P>0.05). The final body weight, weight gain (WG), specific growth ratio, feed conversion ratio and protein efficiency ratio of the fish fed the diet containing 16% SM were similar (P>0.05) to that of the fish fed the control diet. Except lipid, digestible contents of dry matter, crude protein, ash, gross energy and individual amino acids decreased while phosphorous increased with increasing SM levels. No significant differences were observed in whole‐body dry matter, ash and lipid contents among all the treatments (P>0.05); crude protein contents between fish fed the control diet and a diet containing 24% SM were also not affected significantly (P>0.05), and the phosphorus content was not significantly different when the SM level was increased to 32% (P>0.05). No significant negative differences were observed in the liver composition between fish fed the control diet and the diet containing 24% SM. The most efficient diet in terms of cost per unit WG of fish was obtained in 8% SM dietary substitution, while no significant differences were found among the 0%, 8% and 16% levels. It was indicated that SM can be utilized in the juvenile Nile tilapia diet to replace about 16% of SBM protein without causing negative effects on growth performance, body composition, liver composition and feed utilization.     

Dietary taurine enhances growth and feed utilization in larval Nile tilapia (Oreochromis niloticus) fed soybean meal‐based diets

This study was conducted to evaluate the effects of dietary taurine on growth performance and feed utilization of Nile tilapia (Oreochromis niloticus) larvae. Four plant protein‐based, isonitrogenous (400 g kg^?1 protein), isoenergetic (19 MJ kg^?1) diets supplemented with four taurine concentrations (0.0, 5.0, 10.0 and 15.0 g kg^?1; designated as T₀, T_0.5, T₁ and T_1.5, respectively) were prepared. The diets were fed to triplicate groups of fish larvae (0.024 g average body weight), to apparent satiation, three times per day for 60 days. Larval growth rates and feed utilization efficiency were significantly improved with increasing supplemental taurine up to 10 g kg^?1 and decreased with further taurine supplementation. The quadratic regression analyses indicated that the maximum larval performance occurred at about 9.7 g kg^?1 of total dietary taurine. Fish survival was significantly lower at 15 g kg^?1 dietary taurine than at other taurine levels. Body protein significantly increased, while body moisture and ash decreased, with increasing dietary taurine up to 10 g kg^?1 and decreased with further taurine supplementation to 15 g kg^?1. Body lipid was not significantly affected by dietary taurine concentration. A number of body amino acids (tryptophan, arginine, histidine, leucine, isoleucine, valine, alanine, glycine, threonine and taurine) significantly increased with increasing supplemental taurine up to 10 g kg^?1 and then decreased with further increase in dietary taurine levels. The rest of body amino acids were not significantly affected by dietary taurine. The present results suggest that about 9.7 g kg^?1 dietary taurine is required for optimum performance of Nile tilapia larvae fed soybean meal‐based diets.     

Growth performance and feed utilization of Nile tilapia Oreochromis niloticus (Linnaeus, 1758) and tilapia galilae Sarotherodon galilaeus (Linnaeus, 1758) fingerlings fed plant protein-based diets

This study was designed to determine the effect of complete substitution of fish meal (FM) by three plant protein sources including extruded soybean meal (SBM), extruded full‐fat soybean (FFSB) and corn gluten meal (CGM) on growth and feed utilization of Nile tilapia Oreochromis niloticus and tilapia galilae Sarothrodon galilaeus. Four isonitrogenous of crude protein (ca. 28.0%) and isocaloric (ca. 19 MJ kg⁻¹) experimental diets were formulated. The control diet (diet 1) was prepared with FM as the main protein sources. Diets 2–4, each FM control diet, were completely substituted with SBM (diet 2), FFSB (diet 3) and CGM (diet 4). l ‐lysine and dl ‐methionine were added to plant protein diets to cover the nutritional requirements of tilapia. Each treatment was allocated to three net pens and fed for 17 weeks. Nile tilapia fed the control diet showed significantly higher (P≤0.05) values for final body weight (FBW), feed intake (FI), weight gain (WG) and specific growth rate (SGR), whereas fish fed the diet with CGM achieved the lowest values. Tilapia galilae fed SBM diet recorded the highest (P≤0.05) values for growth performance. Better feed conversion ratio (FCR) for both Oreochromis niloticus and Sarothrodon galilaeus was observed when fish were fed SBM diet, whereas the worse FCR was recorded for FFSB diet. Feed utilization parameters including protein productive value (PPV), fat retention (FR) and energy retention (ER) showed significant differences (P≤0.05) for both the species fed different dietary protein sources. The present results suggest that, for Nile tilapia, both SBM and FFSB supplemented with dl ‐methionine and l ‐lysine can completely replace dietary FM. Meanwhile, S. galilaeus fed SBM diet exhibited comparable growth and feed utilization with those fish fed a fish‐meal‐based diet.     

Complete replacement of fish meal by porcine and poultry by-product meals in practical diets for fingerling Nile tilapia Oreochromis niloticus: digestibility and growth performance

The apparent digestibility coefficients (ADC) of poultry by-product meal-pet food grade (PBM) and porcine meal (PM) were determined for fingerling male Nile tilapia. ADC for protein were 98.1% and 92.3% in PBM and PM, and 87.1% and 79.4% for energy. PBM and PM were then used as complete replacements for fish meal (FM) in practical diets for Nile tilapia formulated to contain equal digestible protein (300 g kg⁻¹) and energy (16.74 MJ per 100 g) on an as-fed basis. Fingerlings (mean initial weight ±SD, 9.5 ± 0.015 g) were fed for 8 weeks on one of the four diets: FM-, PBM- or PM-based and a commercial feed. The ADC for protein in control and PBM diets (89.7% and 87.9%) were significantly higher than those for the control diet (81.96%). Growth performance and feed utilization were statistically similar between fish fed control and PBM diets, whereas the PM diet exhibited significantly lower performance compared with the control. However, the PM diet showed similar results to the commercial reference diet. Survival and feed conversion ratio were not significantly influenced by replacement of FM with either PBM or PM. The results indicated that PBM and PM can effectively replace FM in practical diets for fingerling Nile tilapia.     

Salmon testes meal as a functional feed additive in fish meal and plant protein‐based diets for rainbow trout (Oncorhynchus mykiss Walbaum) and Nile tilapia (Oreochromis niloticus L.) fry

Fishery processing by‐products are a large resource from which to produce fishmeal and other products for a variety of uses. In this study, testes meal (TM) produced from pink salmon processing by‐product was evaluated as a functional ingredient in aquafeeds. Nile tilapia and rainbow trout fry were fed five isonitrogenous and isoenergetic experimental diets for 4 and 9 weeks respectively. Two diets were fishmeal‐based (FM) and three were plant protein‐based (PP). Salmon TM was added to the FM and PP diets at 7% to replace 20% of fishmeal protein (FMTM and PPTM respectively). An additional control diet was prepared in which fishmeal was added to the PP diet to supply an equivalent amount of protein as supplied by TM (PPFM). Inclusion of TM in both the FM‐ and PP‐based diets resulted in higher final body weights, although differences were only significant between rainbow trout fed FM or FMTM diets. Similar differences were calculated for other indices of fish performance, e.g. specific growth rate, feed conversion ratio, protein efficiency ratio and protein retention efficiency. Feed intake was significantly higher for fish fed FMTM compared with FM in rainbow trout. For tilapia, final weights were numerically higher, but not significantly different for fish fed diets containing TM compared with non‐TM diets (FM vs. FMTM; PP vs. PPTM). Performance of trout or tilapia fed the PPFM diet did not increase compared with the PP diet. The results indicate that TM addition to both FM and PP diets increased feed intake and also increased metabolic efficiency, demonstrating that TM can be a functional ingredient in aquafeeds.     

Nutritional evaluation of waste date fruit as partial substitute for soybean meal in practical diets of juvenile Nile tilapia, Oreochromis niloticus L.

The potential of waste date meal (WDM; low-quality date palm, Phoenix dactylifera L.) as a carbohydrate source in formulated diets for Nile tilapia was evaluated. Four isocaloric-practical diets (15.7 kJ g⁻¹) were formulated incorporating WDM at 0, 100, 200 and 300 g kg⁻¹ levels as partial substitutes for soybean meal (SBM). These were designated D₀ [284 g crude protein (CP) and 383 g carbohydrate (CHO) kg⁻¹ diet], D₁ (279 g CP and 446 g CHO kg⁻¹ diet), D₂ (207 g CP and 495 g CHO kg⁻¹ diet) and D₃ (175 g CP and 578 g CHO kg⁻¹ diet). Each diet was fed to three replicate groups of 30 fish [20.20 ± 0.09 g (±SE)] for 75 days. No feed-related mortality was observed during the entire experimental period. Final body weight (FBW) and specific growth rate (SGR) in the different treatments were statistically not significantly different ( P  > 0.05). Protein efficiency rate (PER) was lowest in diet D₀ and increased with decrease of SBM content (D₁–D₃). A significant increase in whole body lipid content was recorded in fish fed diets D₂ and D₃. Results showed that WDM could be a substitute for SBM up to 300 g kg⁻¹ in practical Nile tilapia diets without compromising growth.     

Amino acid availability and protein digestibility of several protein sources for Nile tilapia,Oreochromis niloticus

Apparent amino acid availability coefficients and protein digestibility of four animal products [fish meal (FM), meat and bone meal (MBM), poultry by‐product and feather meal] and four plant protein‐rich products [soybean meal (SBM), cottonseed meal‐28, cottonseed meal‐38 and corn gluten meal (CGM)] were determined for Nile tilapia, Oreochromis niloticus. Ingredients were incorporated to a practical reference diet at a 7 : 3 ratio (70% of reference diet and 30% of test ingredient). Chromic oxide was used as external digestibility marker. Among animal products poultry by‐product meal (PBM; 89.7%) and FM (88.6%) presented the highest apparent protein digestibility (APD) while MBM (78.4%) and feather meal (78.5%) presented the lowest APD. Among plant protein‐rich products CGM (91.4%) and SBM (92.4%) presented the highest APD values while cottonseed meal‐28 presented the lowest APD (78.6%). Average apparent amino acid availability of feed ingredients was similar to protein digestibility with 92.3%, 89.6%, 73.4%, 80.7%, 88.9%, 84.4%, 91.2% and 79.7% values for SBM, CGM, cottonseed meal‐28 and 38, FM, MBM, PBM and feather meal respectively. These results indicate that O. niloticus is able to utilize efficiently different feedstuffs.     

Evaluation of Cassia fistula meal as a replacement for soybean meal in practical diets of Oreochromis niloticus fingerlings

This study was undertaken to determine the replacement value of Cassia fistula seed meal (CFM) for soybean meal (SBM) in practical diets of Oreochromis niloticus fingerlings. Five practical diets (350 g kg^?1 crude protein) containing 0 g kg^?1 (control), 170 g kg^?1 (diet II), 340 g kg^?1 (diet III), 509 g kg^?1 (diet IV) and 670 g kg^?1 (diet V) substitution levels of CFM for SBM were formulated and fed to triplicate groups of O. niloticus fingerlings (mean initial weight of 10.22 ± 0.03 g) for 70 days. Fish mortality increased linearly with increase in inclusion levels of CFM in the diet. Growth and diet utilization efficiency were depressed in fish fed diets containing CFM at varying inclusion levels. Feed conversion ratio, specific growth rate and protein efficiency ratio of O. niloticus fed on diet containing 170 g kg^?1 substitution level of CFM were similar (P > 0.05) to the control diet. Digestibility of the different diets decreased with increase in inclusion levels of CFM. Fish fed diet containing 670 g kg^?1 CFM had significantly lower carcass protein. However, no significant differences were observed in carcass protein and lipid contents between fish fed the control diets and diet containing 170 g kg^?1 CFM. The most efficient diet in terms of cost per unit weight gain of fish was obtained in 170 g kg^?1 CFM dietary substitution.     

Effects of low and medium levels of red alga Nori (Porphyra yezoensis Ueda) in the diets on growth,feed utilization and metabolism in intensively fed Nile tilapia,Oreochromis niloticus (L.)

A 10‐week feeding experiment was conducted in a respirometric system to evaluate the suitability of red alga Nori (Porphyra yezoensis) as a partial replacement for fish meal in intensively fed Nile tilapia. Diets were formulated to be iso‐nitrogenous and iso‐energetic and to replace 0%, 15% and 30% fish meal with Nori, P. yezoensis. No statistically significant differences in growth or feed utilization between the control diet and either Nori diet were found. Tilapia fed on Nori 15 increased their body mass by 415%, those fed the control diet by 341% and fish fed Nori 30 by 317% over the experimental period. Nori 15 fed fish showed the best feed utilization, highest metabolic growth rate and significantly lower oxygen consumption rates than the control. Both Nori supplemented groups (Nori 15: 4.1 g O₂ g^?1 protein gain and Nori 30: 3.9 g O₂ g^?1 protein gain) used less oxygen per gram of protein gain compared to fish fed the control diet (5.4 g O₂ g^?1 protein gain). Our results show that a low replacement level (15%) of fish meal with Nori improves growth and feed utilization while oxygen consumption and amount of oxygen consumed per gram protein gain are significantly decreased.     

Crude protein levels in diets for two growth stages of Nile tilapia (Oreochromis niloticus) in a biofloc system

Biofloc technology (BFT) provides an additional feed source for aquatic organisms through the conversion of waste in microbial flocs. Because of this, the suitable protein level in a diet for animals in this system could be different from those in conventional systems. Our objective was to determine the suitable protein level in the diet of Nile tilapia juveniles reared with BFT. Two experiments were carried out with tilapia weighing ~10 g (first experiment) and about 50 g (second experiment) during 61 and 98 days respectively. Five crude protein (CP) levels (within 17% and 33%) were tested. The increment of CP resulted in a reduction in dissolved oxygen, pH, alkalinity and an increase in dissolved phosphorus, total suspended solids and total ammonium nitrogen. The crude protein level had a significant effect (p < 0.05) on animal performance. The linear response plateau model was the best fit for the final weight and weight gain data in the two growth phases. In conclusion, tilapia juveniles of 10–60 g and 60–230 g in biofloc can be fed on diets with 28% of CP (26% of digestible protein) and 22% CP (20% of digestible protein) respectively.     

Effects of partial and complete replacement of soybean meal with cottonseed meal on growth,feed utilization and haematological indexes for mono‐sex male Nile tilapia,Oreochromis niloticus (L.) fingerlings

The main objective of this study was to evaluate the effects of replacing soybean meal (SBM) with cottonseed meal (CSM) on the growth performance, feed utilization and haematological parameters of mono‐sex male Nile tilapia fingerlings. Five isonitrogenous diets (containing 31.82% crude protein) containing graded levels of CSM to replace SBM protein were fed to triplicate groups of fish. The diets were supplemented with lysine so that they were similar to the control diet. After a 14‐week feeding experiment, the results revealed that up to 75% of SBM could be replaced by CSM without causing a significant reduction in growth. Fish fed the diet highest in CSM had a significantly lower protein efficiency ratio and a significantly higher feed conversion ratio than fish fed the other diets. High survival was observed in all the dietary treatments, and no significant difference was observed among treatments. The apparent digestibility coefficients (ADC) of dry matter and phosphorus decreased significantly with an increase in the dietary CSM level, whereas the ADC of lipid was not affected by the dietary treatment. The hepatosomatic index and the condition factor were significantly affected by the replacement of SBM by CSM. No significant differences were detected in the moisture, lipid and ash content in whole body and muscle samples, but protein in whole‐body samples was significantly affected by the CSM levels. Significant differences were found in the haemoglobin, haematocrit, red blood cell and white blood cell contents in fish fed diets with different CSM levels. Therefore, these findings suggest that up to 41.25% CSM can be used to replace 75% of SBM protein in diets for mono‐sex male Nile tilapia fingerlings without any adverse effects on the growth performance, feed utilization, body composition and haematological indexes.     

Fisheries by-catch and processing waste meals as ingredients in diets for Nile tilapia, Oreochromis niloticus

Digestibility, feeding and growth studies were conducted with Nile tilapia using diets containing fishery by‐catch and processing waste meals. Three meals manufactured from sorted fisheries by‐catch (MBM, from mixed benthic species, SPM, from small pelagic species, CAM, from mixed catfish species) one from tuna cannery waste (TCW) and one commercial anchovy meal (COM) were tested. By‐catch and processing waste meals had lower protein, lower lipid and higher ash contents than anchovy meal. The meals were all highly digestible and no significant differences (P≥0.05) were observed between apparent protein digestibility measurements. Five feeds, containing fish meal as the major protein ingredient, were formulated and fed to triplicate groups of 30 juvenile tilapias for 9 weeks. Survival, weight gain, specific growth rate (SGR), feed conversion ratio, protein efficiency ratio, phosphorus retention and whole body proximate composition were compared. Weight gain and SGRs were similar for each treatment group and compared favourably with the results obtained from juvenile tilapia elsewhere. Growth was the highest for CAM (P≤0.05), which contained both the highest essential amino acid levels and the highest ash content. Phosphorus retention was significantly lower in fish fed with high ash meals, MBM, CAM and TCW (P≤0.05) than in fish fed with the lower ash meals COM and SPM. Overall, the fisheries by‐catch and processing waste meals evaluated in this study are suitable protein ingredients for juvenile tilapia feeds.     

Effect of dietary protein-energy levels and fish initial sizes on growth rate, development and production of Nile tilapia, Oreochromis niloticus L.

The effects of dietary protein‐energy levels on the growth rate, proximate composition and production were examined in Nile tilapia, Oreochromis niloticus, at two starting weights (22.9 and 39.8 g) reared in concrete ponds for 180 days. The highest weight gain (183.1 g) was obtained with fish fed a 30% protein and 10.5 kJ g^?1 diet for the small initial size and 180.2 g for a diet containing 25% protein and 12.6 kJ g^?1 for the large initial size. Dressed yields (edible mass) and fillets increased to 56.9% and 52.5% in fish fed diet with 25% protein and 10.5 kJ g^?1 at the initial size of 22.9 g, while fish started at 39.8 g exhibited the best values (56.5% and 52.1%) when fed the 30% protein and 10.5 kJ g^?1 diet. Proximate composition of soft tissue (wet weight basis) in small fish was significantly influenced by dietary protein‐energy levels. Protein was 26.1±0.3% in fish fed the high protein (30%) and low energy (10.5 kJ g^?1 diet), while lipid content was 6.4±0.3% at diet containing 20% protein and 14.7 kJ g^?1 diet. Large initial size fish fed the diet with 25% protein and 14.7 kJ g^?1 had the highest body protein (32.0±0.4%) and lowest lipid content (2.2±0.3%). Feed conversion ratio (FCR) and protein efficiency ratio varied with different dietary protein‐energy levels and initial fish sizes. Feed conversion ratio increased with increasing protein and decreasing energy level in the diet, and values in small fish were higher than values in large fish. Protein efficiency ratio decreased with increasing dietary protein level and decreasing energy level. The maximum total production (7.6 tons feddan^?1) was with dietary high protein (30%) and low energy (10.5 kJ g^?1) for small‐sized fish, while large initial fish had the highest production (3.7 tons feddan^?1) when fed the 25% protein and 12.6 kJ g^?1 diet energy. Starting with 22.9 g fish was more advantageous than the initial size of 39.8 g for rearing Nile tilapia. Small fish required a high‐protein and low‐energy diet, whereas large fish required a low‐protein and high‐energy diet to achieve highest production.     

Dietary leucine requirement of Juvenile Nile tilapia,Oreochromis niloticus

An 8‐week feeding trial was conducted to evaluate the effects of dietary leucine on growth performance, feed utilization, body composition and non‐specific immune responses of juvenile Nile tilapia. Five isonitrogenous and isoenergetic diets were formulated to contain graded levels of L‐leucine (5.3, 8.1, 10.9, 13.2, 15.6 and 18.1 g kg^?1 diet, respectively) from dietary ingredients and crystalline L‐leucine. Each diet was randomly assigned to triplicate groups of 20 juvenile fish (1.94 ± 0.01 g) three times daily to apparent satiation. Results showed that the weight gain (WG) and specific growth rate (SGR) increased as dietary leucine concentrations increased from 5.3 to 13.2 g kg^?1 and then decreased slightly with further increase in dietary leucine concentrations. Quadratic regression analysis (y = ?522.6x² + 1304.x + 132.6, R² = 0.684) on weight gain against dietary leucine levels indicated that the optimal dietary leucine requirement was estimated to be 12.5 g kg^?1 diet (corresponding to 43.1 g kg^?1 of dietary protein). Leucine supplementation had no impact on the survival and body composition of tilapia. Serum lysozyme activity of fish fed diet containing 13.2 g kg^?1 leucine significantly increased compared to fish fed diet containing 5.3 g kg^?1. Serum superoxide dismutase activity and immunoglobulin M (IgM) concentration were not significantly affected by dietary leucine supplementation.     

Cyclical feed deprivation and refeeding fails to enhance compensatory growth in Nile tilapia, Oreochromis niloticus L.

A 12-week experiment was carried out to evaluate compensatory growth of 6.6 g Nile tilapia Oreochromis niloticus L. under three cyclical regimes of feed deprivation and refeeding. The deprivation and refeeding regimes included four cycles of 1 week of deprivation and 2 weeks of refeeding (S1F2), two cycles of 2 weeks of deprivation and 4 weeks of refeeding (S2F4) and one cycle of 4 weeks of deprivation and 8 weeks of refeeding (S4F8). A group of fish fed to satiation twice daily throughout the experiment served as control. At the end of the refeeding periods, fish deprived and refed cyclically had higher feed intake and specific growth rates (SGR), but lower body weight, than that of the control fish. There was no significant difference in feed efficiency ratio (FER) between the control and fish subjected to feed deprivation during the refeeding periods, and nitrogen retention efficiency (NRE) was not different between any two treatments throughout the experiment. At the end of the experiment, fish subjected to feed deprivation had lower body weight but similar body composition, relative to those of the control fish. No significant differences were found in final body weight, NRE and body composition between the fish subjected to different cycles of deprivation and refeeding, but the fish subjected to one cycle of deprivation and refeeding exhibited high mortality. Our results indicate that partial growth compensation induced by various cycles of feed deprivation and refeeding does not confer a huge advantage in terms of enhancing the production efficiency and reducing the nitrogen waste output in Nile tilapia farming 29–30 °C.     

Effect of feed colour on growth and feed utilization of Nile tilapia (Oreochromis niloticus L.) larvae and fingerlings

Two experiments were conducted to investigate the effects of feed colour on the performance of Nile tilapia (Oreochromis niloticus) larvae and fingerlings. In the first experiment, triplicate groups of newly hatched larvae (0.01 g fish⁻¹) were stocked in 40 L glass aquaria at a density of 2 fish L⁻¹. The fish were fed a test diet (400 g kg⁻¹ crude protein) with six different colours (dark blue, dark green, red, dark brown, yellow and light brown) for 60 days. The best performance and survival were achieved in fish fed on dark‐coloured diets, while light‐coloured diets (yellow and light brown) resulted in inferior performance. Dark diets also produced higher body protein than light diets. Body water, lipids and ash showed irregular trends. In the second experiment, triplicate groups of Nile tilapia fingerlings (5.30 g fish⁻¹) were stocked in 140‐L aquaria, in a recirculating indoor system. The fish were fed a test diet (350 g kg⁻¹ crude protein) with the same colours used in the larval trial, for 60 days. Growth rates, feed efficiency, survival and body composition were not significantly affected by feed colours. These results suggest that Nile tilapia larvae are visual feeders, and they prefer dark‐coloured diets to light‐coloured diets, while fingerling fish showed no preference to diet colours.