Dry whey meal as a protein source in practical diets for Nile tilapia,Oreochromis niloticus fingerlings

ABSTRACT

This study was conducted as a trial of using dry whey meal (DWM) as a substitute for fish meal (FM) in practical diets for Nile tilapia, Oreochromis niloticus. Triplicate fish groups were fed on five isonitrogenous (30.2%) and isolipidic (6.9%) diets. The control diet (D1) used FM as the sole protein source. In the other four diets (D2–D5), FM protein was substituted by 25, 50, 75, or 100% DWM. Fish (3.5 ± 0.1 g) were stocked at a rate of 20 fish per 100-L aquarium and fed one of the tested diets up to satiation twice daily for 12 weeks. Fish growth, feed utilization, protein efficiency ratio, apparent protein utilization, and energy utilization for fish fed DWM diets up to 75% FM (D2–D4) tended to be higher but were not statistically different than the control diet. No significant effect of diet was found in whole-body moisture, crude protein, and total ash contents. Whole-body lipid content in fish fed the 100% DWM (D5) diet was significantly higher than that for fish fed the control diet. The optimal replacement level of FM by DWM was estimated by second-order polynomial regression to be 62.5%.     

Utilization of torula yeast (Candida utilis) as a protein source in diets for tilapia (Oreochromis mossambicus Peters) fry

A 63  day^–1 feeding trial was conducted under laboratory conditions to evaluate the effects of substituting animal protein with a mixture of plant feedstuffs including 25, 30, 35, 40 and 45% of the protein with torula yeast ( Candida utilis ), 20% with soybean meal and 15% with Alfalfa Leaf Protein Concentrate (ALC), in diets for tilapia ( Oreochromis mossambicus Peters) fry. Feeding efficiency was compared against a diet with fish meal as the sole protein source. Diet nutritional quality was very similar independent of composition, with no differences in growth parameters, but fish fed with 30% yeast diet showed the best growth performance. Diet composition did not affect feed or protein utilization, with the best feed conversion ratio, protein efficiency ratio and apparent nitrogen utilization in the 25% yeast diet. Protein digestibility was above 80% for all diets, and no differences in carcass composition were observed. The best incidence cost was obtained with 25% yeast and the highest profit index with 30% yeast, but no statistical differences were observed with the other treatments. The results suggest that it is possible to replace up to 65% of animal protein with a mixture of plant proteins, including 30% from torula yeast, in tilapia fry diets without adverse effects on fish performance and culture profit.     

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.     

The potential for rice wine residual as an alternative protein source in a practical diet for Nile tilapia (Oreochromis niloticus) at the juvenile stage

This study investigated the utilization level of rice wine residual (RWS) in a diet for juvenile Nile tilapia. The effects of RWS in diets were evaluated for growth (at week 4), fillet composition, haematological and blood chemical parameters (at weeks 3 and 6) and intestinal morphology (at week 6). The dietary treatments (each diet in triplicate groups) consisted of seven isonitrogenous (320 g kg^?1 crude protein) servings that were formulated to include RWS at levels of 0 (control diet), 75, 150, 225, 300, 375 and 450 g kg^?1 dry diet (Diets 1–7, respectively) and a commercial diet (Diet 8). The growth performances of fish in the groups on Diets 1–4 did not differ significantly. There were no marked variations in fillet composition, serum lysozyme, haematological profiles and blood urea nitrogen (BUN) among treatment diets, except for haematocrit and BUN (week 3) and haemoglobin (week 6) of fish on Diets 6–7. While the blood glucose increased as the amount of RWS incorporation increased (P < 0.05), the cholesterol decreased (P < 0.05). Only intestinal morphometry of fish fed Diet 7 differed significantly from any of the other treatments. Taken together, RWS (at 225 g kg^?1 diet) has the potential for use in juvenile Nile tilapia diet without negative effects.     

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 ideal protein concept for precision formulation of amino acid levels in fish-meal-free diets for juvenile Nile tilapia (Oreochromis niloticus L.)

This study was undertaken in a closed system with Nile tilapia (Oreochromis niloticus) to examine the effects of total replacement of fish meal (FM) by soybean meal. Nile tilapia fingerlings with an average weight of 5.34±0.08 g were hand‐fed one of the five isoenergetic (≈13.5 MJ digestible energy kg^?1) and isoproteic (≈31% of digestible protein) experimental diets to satiation, six times a day during 85 days in eight replicate fibreglass tanks (six fish per tank). The control diet containing FM was substituted by soybean meal, with and without essential amino acids (lysine, methionine and threonine) or dicalcium phosphate supplementation. The supplemental amino acids were added at levels to simulate the reference amino acid profile of Nile tilapia carcass protein, based on the ideal protein concept. The results showed that soybean meal diet supplemented only with dicalcium phosphate was inferior to the control diet with FM and soybean meal diets supplemented with dicalcium phosphate and essential amino acids. Multiple essential amino acids and dicalcium phosphate incorporation in soybean meal diets was associated with performance, whole‐body composition and carcass yield equal to that of the fish fed with the control diet containing FM. These data suggest that a diet with all plant protein source, supplemented with essential amino acids, based on tissue amino acid profile, can totally replace FM in a diet for Nile tilapia, without adverse effects on the growth performance, carcass yield and composition.     

无鱼粉饲料中添加磷和植酸酶对奥尼罗非鱼生长性能及体成分的影响

奥尼罗非鱼(Oreochromis niloticus×O.aureus)幼鱼的初始体重约5.0 g,试验共设5组饲料,以全鱼粉饲料为对照组(D0),以豆粕和花生粕完全替代鱼粉为试验组,其中两组为不补充磷酸二氢钙的情况下不添加植酸酶(D1)和添加植酸酶(D2),另两组为在补充磷酸二氢钙的情况下不添加植酸酶(D3)和添加植酸酶(D4)。每一饲料组设3个重复,每箱养鱼30尾,在流水系统中饲养,表观饱食投喂,投喂率为5%~6%。饲养实验周期为8周。试验结果表明,添加磷组(D3、D4)和全鱼粉组(D0)的特定生长率和饲料系数在组间差异不显著(P>0.05),但显著高于不添加磷组(D1、D2)(P<0.05);磷的表观消化率在添加植酸酶组(D2、D4)均显著高于不添加植酸酶(D1、D3),但与全鱼粉组(D0)差异不显著;鱼体粗蛋白含量在不添加磷和植酸酶组(D1)显著低于其他4组;体粗脂肪含量在不添加磷(D1、D2)组显著高于其他组;体灰分含量由高到低依次为全鱼粉组(D0)、添加磷和植酸酶组(D4)、添加磷不添加植酸酶组(D3)、不添加磷添加植酸酶组(D2)和不添加磷不添加植酸酶组(D1),且两两组间差异显著;体钙、磷、镁、锌含量和脱脂骨灰分、钙、磷含量在全鱼粉组(D0)最高。不添加磷组(D1、D2)血清磷含量显著低于其他3组,而血清碱性磷酸酶活性显著地高。试验结果说明,无鱼粉饲料中补充磷可保持奥尼罗非鱼幼鱼生长率,饲料利用和全鱼可食部分营养成分含量;同时添加植酸酶,能显著提高饲料中磷的利用率,促进磷、锌和镁在鱼体内沉积,并有进一步提高奥尼罗非鱼幼鱼生长和饲料利用的趋势。[中国水产科学,2006,13(1):112-118]     

投喂频率对尼罗系吉富罗非鱼幼鱼胃排空、生长性能和体组成的影响

通过胃排空试验与养殖试验研究了不同投喂频率对尼罗系吉富罗非鱼幼鱼的胃排空、生长性能以及体组成的影响.在试验开始时,观测尼罗系吉富罗非鱼幼鱼的胃内饲料排空情况,胃排空试验结果表明,胃排空率的最佳描述为平方根函数,胃内饲料在饱食投喂后15 h左右完全排空,达到投喂前水平,80％胃排空为9h,也就是投喂后大约9h恢复食欲.360尾试验鱼(初始体质量3.72 g)以不同的投喂频率(1d4次、1d3次、1d2次、2d4次、2d3次、2d2次)分组,每组设立3个平行组,随机养殖于18个网箱中,每箱养殖20尾鱼,按饱食量投饲膨化饲料.养殖期为6周.尼罗系吉富罗非鱼幼鱼在投喂频率为1d4次、1d3次和1d2次时特定生长率和饲料效率显著高于投喂频率为2d4次、2d3次和2d2次时(P＜0.05);投喂频率为1d2次、2d4次、2d3次和2d2次时其摄食量显著低于1d4次和1d3次时(P＜0.05).随着投喂频率降低,鱼体水分含量逐步上升,脂肪和蛋白质含量逐步下降,其中1d4次、1d3次组鱼与2d2次组鱼有显著性差异(P＜0.05).各投喂频率组间的肝体指数无显著性差异(P＞0.05).3.7～48.0 g尼罗系吉富罗非鱼幼鱼的适宜投喂频率为1d2次,较2d2次、2d3次和2d4次时明显提高了生长速度和饲料效率,较1d3次、1d4次摄食量显著降低.2种试验结果较为一致.     

吉富罗非鱼生长过程中氮收支变化的研究

为充实有关鱼类研究数据,提供实际生产理论依据,研究了吉富品系尼罗罗非鱼（Oreochromis niloticus）从鱼种（18 g）生长至成鱼（180 g）过程中氮收支变化。试验为期73 d,每日饱食投喂并收集鱼粪,溶解氧质量浓度为8.0-6.0 mg·L-1,pH为 7.5-6.5,水温为24-30 ℃。在鱼均质量达到50 g、100 g和180 g时测定并计算当前生长阶段氮收支。结果表明,生长氮比例在养殖初期最高（64%）,养殖中期最低（47%）;粪氮比例在养殖中期最高（9%）,养殖初期和末期分别为5%和4%;排泄氮比例随鱼的生长而逐渐增加。此外,试验期间水中总氮增加速度在养殖中期减慢,养殖末期再次加快。     

Osmoregulatory actions of growth hormone in juvenile tilapia (Oreochromis niloticus)

Growth hormone (GH) effectively promotes seawater (SW) adaptation in salmonids, but little is known of its effect in tilapias. Experiments were performed to investigate the effects of recombinant eel GH (reGH) on osmoregulatory actions and ultrastructural features of gill chloride cells in juvenile tilapia, Oreochromis niloticus. Tilapia showed a markedly improved SW survival, when directly transferred from freshwater (FW) to 62.5% SW 24h after a single reGH injection (0.25 or 2.5 µg g^-1) or 3 reGH injections (0.25 µg g^-1 every other day). Plasma Na+ and Mg²⁺ levels were significantly reduced by reGH (0.25 and 2.5 µg g^-1) compared with saline injections; Ca²⁺ concentrations were reduced significantly by high dose of reGH (2.5 µg g^-1) after SW transfer. However, fish failed to survive more than 24h when directly transferred to 70% SW, although the fish treated with reGH could survive longer than the controls. When examined by electron microscopy, the chloride cells were identified as mitochondrion-rich and an extensive tubular system was induced by GH treatment. The results of the present study suggest that, similar to its effect on salmonids, GH also exerts acute osmoregulatory actions and enhances SW adaptation in juvenile tilapia. GH also stimulates the differentiation of chloride cells toward SW adaptation.     

Nutrient composition and sensory evaluation of fillets from wild-type Nile tilapia (Oreochromis niloticus, Linnaeus) and a red hybrid (Florida red tilapia × red O. niloticus)

A comparison of composition and sensory evaluation were performed on fillets of Oreochromis niloticus (wild type) and red hybrid tilapia (RHT) (Florida red tilapia ♂× red O. niloticus♀). Fifty male tilapia, 25 O. niloticus (initial weight 159.3 g) and 25 red hybrid (initial weight 132.4 g), were placed in each of three 2.0 m³ volume tanks. The fish were fed a commercial feed containing 35.9% crude protein during the 120‐day experimental period and then killed in cold water (3°C). All the fish were filleted. Twelve fillets from each treatment were used for proximate analyses, five fillets from each treatment were used for fatty acids analyses and the remaining fillets were used for sensory evaluation. The compositional analyses showed similar moisture, true protein and ash content in both genetic groups, but a lower crude fat content was measured in the red hybrid fillets (0.70%) compared with that of O. niloticus fillets (0.97%). No differences between O. niloticus and the red hybrid were observed in their fillet profile of fatty acids. In the sensory evaluation test, a difference in fillet flavour between both genetic groups was perceived. Of the 112 consumers in the preference test, 81.2% perceived a difference in fillet flavour between the two tilapias, with a general preference for the red hybrid over the wild‐type O. niloticus. The benefits of cultivating a RHT with a low lipid content are discussed.     

Optimizing diets to decrease environmental impact of Nile tilapia (Oreochromis niloticus) production

Aquaculture is one of the most thriving animal production sectors, and Nile tilapia (Oreochromis niloticus) farming represents 8% of total finfish culture. However, the industry sustainability depends on the development of cost‐effective and environmental friendly feeds. This study aimed to reduce dietary protein levels in diets for juvenile tilapia and to minimize diet environmental impact while maximizing biological efficiency. A growth trial was performed using five isoenergetic plant protein‐based diets with decreasing levels of crude protein: 360, 340, 320, 300 and 280 g/kg diet (D360, D340, D320, D300 and D280, respectively). Dietary protein utilization was assessed by metabolic trials using a radiolabelled amino acid mixture. Tilapia in all treatments showed similar growth performance and feed intake. Feed conversion ratio was significantly higher in fish fed the D280 than the D360 diet, while no differences were found for other treatments. Protein retention was significantly higher in tilapia fed the D300 than the D360 diet. Amino acid catabolism increased in fish fed the D360 diet, though without significant differences in muscle amino acid retention. This study demonstrates that dietary protein levels can be reduced to 300 g/kg diet without hindering tilapia growth and feed conversion ratio, while reducing environmental nitrogen losses.     

Comparison of growth, fillet yield and proximate composition between Stirling Nile tilapia (wild type) (Oreochromis niloticus, Linnaeus) and red hybrid tilapia (Florida red tilapia×Stirling red O. niloticus) males

A comparison was made of some productive traits of Stirling Nile tilapia (wild type) (Oreochromis niloticus, Linnaeus) and red hybrid tilapia (Florida red tilapia× Stirling red O. niloticus) males during a 98‐day grow‐out period. Twenty‐two males from each genetic group with initial weights of 139.0 g for O. niloticus and 207.3 g for the red hybrid were placed in triplicate tanks. The fish were fed with a feed containing 36.8% crude protein. Survival was 97.0% for the red hybrid and 83.3% for O. niloticus. Daily individual weight gains were 2.95 and 2.50 g and final body weights were 473.0 and 348.8 g for the red hybrid and O. niloticus respectively. Fillet yield was similar for both the species, with 33.4% for the red hybrid and 32.0% for O. niloticus. Fresh fillet lipid content was perceptibly less in the red hybrid (0.33%) than in O. niloticus (2.07%). Some benefits of a red low‐fat tilapia genotype are discussed.     

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.     

Optimum selenium requirement of juvenile Nile tilapia,Oreochromis niloticus

A feeding experiment was conducted to determine the optimum selenium requirement in juvenile Nile tilapia. Each of six purified diets with Se‐methionine levels at 0.05, 0.21, 0.41, 0.57, 0.79 and 1.00 mg/kg was assayed in triplicate with initial body weight of 3.00 ± 0.01 g for 8 weeks. The growth of fish was obviously increased when the dietary Se was less than 0.57 mg/kg diet and reached a plateau when the dietary Se was ≥0.57 mg/kg. Serum and hepatopancreatic glutathione peroxidase (GPx) activity increased markedly when the dietary Se was less than 0.57 mg/kg, but then decreased when the dietary Se was higher than 0.57 mg/kg. The malondialdehyde contents in hepatopancreas were significantly decreased when the dietary Se was higher than 0.79 mg/kg. No significant differences were observed in hepatopancreatic total antioxidant capability (T‐AOC) among the groups (p > .05). The results of this study indicated that Se addition as Se‐methionine was essential, while both the deficiency and excess levels of dietary Se would cause negative effects on growth or antioxidant capability in juvenile Nile tilapia. Based on broken‐line regression of WG and piecewise regression of liver GPx, the optimum requirement of Se for juvenile Nile tilapia is 0.57 mg/kg diet.     

Sunflower seed meal as a protein source in diets for Tilapia rendalli (Boulanger, 1896) fingerlings

This study tested the use of sunflower seed meal as a dietary protein replacement for fishmeal in practical diets for tilapia fingerlings. In order to determine the optimum substitution level for this species, sunflower seed meal was used to replace 10%, 20%, 30%, 40% and 50% of the fishmeal protein in diets containing 40% protein overall. During a 70‐day feeding period, diets containing 10% and 20% plant protein provided the best growth and feeding efficiency results, with values statistically similar to those of the control diet based on fishmeal as the sole protein. The unitary feeding cost index showed the highest profit with diets containing 20% sunflower seed meal. Growth depletion observed with diets containing higher sunflower seed meal percentages is explained by increasing Phe and Met deficiencies, and high non‐digestible fibre content. It was concluded that sunflower seed meal is a suitable feed ingredient for tilapia complete diets when it constitutes up to 20% of the dietary protein.     

吉富罗非鱼成鱼胆碱的最适需要量

选用初始体质量为(220.00±8.34) g的吉富罗非鱼(Oreochromis niloticus)360尾, 随机分成6组,每组3重复(每重复20尾), 于1 m×1 m×1.5 m池塘网箱中饲养。分别饲喂胆碱含量为97.80(对照组)、375.04、565.74、974.27、      1 409.81、1 824.35 mg/kg的半纯化饲料10周, 研究胆碱对吉富罗非鱼成鱼生长、饲料利用、鱼体营养组成、胆碱蓄积量及部分血液生化指标的影响。结果显示, 经过10周的饲喂, 饲料中添加胆碱可显著提高鱼体增重率、特定生长率和饲料效率(P<0.05); 降低肝脂肪含量(P<0.05), 提高肌肉脂肪含量(P<0.05); 显著升高肝胆碱蓄积量(P<0.05); 胆碱添加组血清甘油三酯(TG)和总胆固醇(T-CHO)显著高于对照组(P<0.05), 并随饲料胆碱含量增加呈现升高的趋势; 肝甘油三酯(TG)和总胆固醇(T-CHO)随着胆碱含量的增加而显著降低(P<0.05); 血清谷草转氨酶(ALT)、谷丙转氨酶(AST)和碱性磷酸酶(ALP)均随着饲料胆碱含量的增大而显著降低(P<0.05)。结果表明, 饲料中添加适量的胆碱可以改善吉富罗非鱼成鱼的生长性能, 提高饲料利用效率, 降低肝脂肪含量, 促进肝脂肪转运; 对特定生长率进行回归分析, 得出吉富罗非鱼成鱼对饲料中胆碱的最低需要量为506.43 mg/kg, 而对肝胆碱蓄积量回归分析得出的需要量为981.38 mg/kg。

     

Dietary phosphorus requirement of GIFT strain of Nile tilapia Oreochromis niloticus reared in freshwater

A study was conducted to estimate the optimum requirement of dietary available phosphorus for GIFT strain of Nile tilapia Oreochromis niloticus. Six purified diets were formulated to contain graded levels (0 (control diet), 2.9, 4.8, 7.6, 9.1 and 10.9 g kg^?1 diet) of available phosphorus. Each diet was fed to triplicate groups of 12 fish with initial average weight (46.03 ± 2.14) g for 8 weeks. The results showed that fish fed the three lowest phosphorus diets (0, 2.9 and 4.8 g kg^?1) had significantly lower weight gain rate, specific growth rate (SGR) and feed efficiency than those fed the other diets (P < 0.05). The survival rate of fish fed the control diet was significantly lower than that of the fish fed the other diets (P < 0.05). Whole body viscerosomatic index and crude lipid content decreased significantly with increasing dietary available phosphorus levels (P < 0.05), while the contents of crude ash, calcium, phosphorus in the whole body and vertebrae showed the opposite trend (P < 0.05). The blood chemistry analysis showed that dietary available phosphorus had significant effects on serum phosphorus concentration, enzyme activities of alkaline phosphatase and parathyroid hormone level. Quadratic curve analysis based on SGR indicated that the minimum dietary requirement of available phosphorus for maintaining optimal growth of tilapia was 8.6 g kg^?1.     

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.