微粒饲料替代生物饵料对大黄鱼稚鱼生长、存活和消化酶活力的影响

以初始体重为(1.93±0.11) mg的大黄鱼稚鱼(12日龄)为实验对象,以微粒饲料(micro-diet,MD)分别替代0%、25%、50%、75%和100%生物饵料(live prey,LP),探讨微粒饲料替代生物饵料对大黄鱼稚鱼生长、存活、体成分和消化酶活力的影响.30 d的摄食生长实验表明:微粒饲料替代生物饵料显著影响大黄鱼稚鱼的生长、存活、体成分和消化酶活力.当微粒饲料替代50%和75%生物饵料时,两组间的特定生长率(SGR)差异不显著(P＞0.05),但均显著高于100%替代水平(P＜0.05);同时,75%替代水平SGR显著高于0%和25%替代水平(P＜0.05).存活率在各处理组间的差异关系与SGR的变化趋势类似.鱼体粗蛋白含量随替代水平的升高有下降的趋势,其中50%、75%和100%替代水平鱼体粗蛋白含量显著低于0%和25%替代水平(P＜0.05),而鱼体粗脂肪含量变化趋势与之相反.当微粒饲料替代100%生物饵料时,其胰段和肠段淀粉酶活力显著高于其余各处理组(P＜0.05),而其余各处理组之间淀粉酶活力差异均不显著;微粒饲料替代生物饵料对各处理组蛋白酶活力无显著影响.由此可以看出,大黄鱼苗种生产中,在12日龄以后使用优质微粒饲料替代50%～75%的生物饵料是可行的.     

Evaluation of various diets for the optimum growth and survival of larvae of the penaeid prawn Penaeus japonicus Bate

Four types of food were tested to determine their effects on the growth and survival of larvae of the penaeid shrimp Penaeus japonicus Bate. The food types were live cells of Candida utilis (yeast), freeze-dried Candida utilis, microparticulate diet, and microencapsulated diet (commercial product). The diatom Chaetoceros gracilis was fed to larvae as a control. Two sets of experiments were carried out; the first was run in outdoor 1.5 ton tanks, and the second in indoor 1.2 ton tanks. In the outdoor experiment, the best survival and growth from nauplius to postlarva stage were obtained using microparticulate diet. During the first week of culture, freeze-dried Candida utilis resulted in the highest growth and survival among examined diets, but both factors dropped dramatically after the mysis stage. In the indoor experiment, the best growth and survival were obtained using live cells of Candida utilis from nauplius stage to end of mysis stage followed by brine shrimp. Tested diets were analysed for their contents of crude protein, total lipids, total carbohydrates, amino acid profiles and fatty acid contents.     

Trypsin enzyme activity during larval development of Litopenaeus vannamei (Boone) fed on live feeds

Larval stages of the Pacific white shrimp, Litopenaeus vannamei (Boone) were fed standard live diets of mixed microalgae from the first to the third protozoea (PZ1 to PZ3), followed by Artemia nauplii until post‐larvae 1 (PL1). Trypsin enzyme activity for each larval stage was determined using N‐α‐p‐toluenesulphonyl‐l ‐arginine methyl ester (TAME) as a substrate. Results were expressed as enzyme content to assess ontogenetic changes during larval development. Tissue trypsin content (IU µg^?1 DW for each larval stage) was significantly highest at the PZ1 stage and declined through subsequent stages to PL1. This contrasts with previously observed patterns of trypsin development in Litopenaeus setiferus (Linnaeus) and other penaeid genera, which exhibit a peak in trypsin activity at the third protozoea/first mysis (PZ3/M1) larval stage. Litopenaeus vannamei larvae transferred to a diet of Artemia at the beginning of the second protozoea (PZ2) stage were significantly heavier on reaching the first mysis stage (M1) than those fed algae, while survival was not significantly different between treatments. At both PZ2 and PZ3 stages, trypsin content in larvae feeding on Artemia was significantly lower than in those feeding on algae. The rapid decline in trypsin content from PZ1 and the flexible enzyme response from PZ2 suggest that L. vannamei is physiologically adapted to transfer to a more carnivorous diet during the mid‐protozoeal stages.     

Effects of microalgal diets on larval growth and survival of Paphia malabarica chemnitz

The effects of food availability on the larval growth and survival of Paphia malabarica were studied in two experiments by feeding the larvae with six algal diets. Newly hatched larvae of P. malabarica were fed with six different marine microalgae species, singly and in a combination of two species. The best growth was with Isochrysis galbana and Nannochloropsis salina as a single species of diet. The nutritional value of single‐species diets was in the order of N. salina, I. galbana, Dicrateria inornata, Chaetoceros calcitrans, Tetraselmis gracilis and Dunaliella salina. Of the mixtures tested, 50%I. galbana/50%N. salina supported growth and metamorphosis equivalent to those of the I. galbana control.     

Growth performance of the early life stages of broad‐nosed pipefish,Syngnathus typhle (L.) fed different live or frozen diets

This work tested the effect of using different live and frozen feed on the growth performance of Syngnathus typhle. It was divided into two experiments. In Experiment I Artemia and Atlantic ditch shrimp (Palaemonetes varians) larvae were used as live diets, whilst in Experiment II frozen mysids Mesopodopsis slabberi and frozen P. varians were used. At the end of the first experiment juvenile pipefish grew significantly more when fed P. varians (P < 0.05) with an overall Weight Gain (WG) of 914.8 ± 79.3% bw day^?1, compared to Artemia fed fish (WG = 683.2 ± 14.7%). Both mean Specific Growth Rate (SGR) and survival were similar between dietary treatments and did not vary significantly (P > 0.05). In Experiment II juveniles were weaned with frozen diets but no significant differences were found between the two tested diets in all parameters tested. Final WG was 516.5 ± 63.3% and 566 ± 17.6%, and Feed Conversion Ratio (FCR) was 30 ± 1.5% and 28.2 ± 1.2% for animals fed P. varians and M. slabberi respectively. Results indicate that P. varians is an adequate diet to use during initial stages of the S. typhle life cycle and should be considered as a frozen diet for subsequent life stages of this species as an alternative to currently known natural diets.     

Growth, survival, lipid and fatty acid profile of juvenile monaco shrimp Lysmata seticaudata fed on different diets

The present work evaluated the effect of three inexpensive diets (frozen minced mussel and edible cockle (MMC), frozen minced squid (MS) and gilthead seabream feed (GSF)) on growth, survival, sex reversal, lipid classes and fatty acid (FA) profile of juvenile ornamental shrimp Lysmata seticaudata. Shrimp fed GSF displayed the highest survival rate (±SD) (85.2±1.8%) and the highest percentage (±SD) of shrimp changing from male to simultaneous hermaphrodite (SH) phase (25.2±2.2%). All diets promoted growth rates superior to those reported in the wild, with SH shrimp displaying higher total lengths (TL). Shrimp in SH phase fed GSF displayed the highest TL (±SD) (40.6±1.2 mm). Cultured shrimp reflected the lipid content of experimental diets, with shrimp fed GSF displaying the highest triacylglycerols and sterols (ST) contents. The higher rearing density induced by lower mortality rates of shrimp fed GSF, and the high ST levels present in the diet, may explain the higher proportion of shrimp in SH phase. The higher levels of highly unsaturated fatty acids (HUFA) displayed by MS did not promote higher survival or growth rates. The low polyunsaturated fatty acids and HUFA content of MMC was not reflected in cultured shrimp, probably because of a selective retention of these FA.     

Effect of microencapsulated diets supplemented with genetically modified bacteria on the growth and survival of Fenneropenaeus indicus postlarvae

Microencapsulated diets were prepared and supplemented with two genetically modified bacteria that produced digestive enzymes. One produced a protease (strain Escherichia coli XL1Bluep635), and the other a lipase and a protease (strain E. coli XL1Bluep7). Fenneropenaeus indicus at the postlarval 1 stage (PL1) were fed these diets for 16 days, and their total length and survival were recorded every 2 days. The results were analyzed by anova and sequential Turkey–Kramer analysis. Shrimp fed on the diet supplemented with strain E. coli XL1Bluep635 (diet 635) exhibited the fastest growth rate of 0.26 mm day⁻¹, followed by shrimp fed on the control commercial unsupplemented diet CD2 – 0.21 mm day⁻¹, and shrimp fed on diet supplemented with strain E. coli XL1Bluep7 (diet 7) – 0.20 mm day⁻¹. The growth rates of shrimp fed on diet supplemented with control strain E. coli XL1BluepUC19 (diet XL1), and those fed on unsupplemented diet prepared in our laboratory (D2), were 0.15 and 0.14 mm day⁻¹, respectively. The survival of shrimp fed on diets CD2 and 635 showed the same level of survival of 83.3%, followed by those fed on diet D2 with 76.6%. Shrimp fed on diet 7, showed 71.6% survival, and those fed on diet XL1, 55%.     

Effects of different diets on larval development in a peppermint shrimp (Lysmata sp. (Risso))

Currently, only a handful of marine ornamental species are commercially produced through aquaculture. In order for the marine aquarium industry to continue to grow, a diverse selection of cultured animals is required to offset wild collections. Long and variable larval durations are the major bottleneck for mass production of marine ornamental shrimp. Improving larval diet may reduce the larval duration and enhance the prospects of commercial aquaculture. A laboratory study was conducted to examine the effect of different diets on larval development and survival of the peppermint shrimp, Lysmata (gulf coast variety), a popular aquarium shrimp. The effect of three feeding regimes [Artemia alone (ART), ArteMac? alone (COMM) and Artemia in combination with ArteMac? (ART/COMM)] on survival and development were tested. Survival to zoea 5 for both ART and ART/COMM treatments was 99%, but only 62.5% for COMM treatment. ArteMac? alone treatment shrimp only survived to zoea 7. Survival to postlarvae for ART treatment (72.5%) was significantly lower (P<0.01) than those of treatment ART/COMM (80.5%). Larvae fed ART/COMM had significantly (P<0.01) shorter larval duration than larvae fed ART. Fourteen days after the first postlarva appeared, the rates of settlement (85.4% and 67.5% respectively) and survival (68.8% and 49.0% respectively) were significantly greater (P<0.01) for larvae fed the ART/COMM than those fed ART.     

Growth performance,survival and body composition of southern flounder Paralichthys lethostigma larvae fed different formulated microdiets

Three experiments were conducted to evaluate the effects of micro‐bound diets (MBD) on southern flounder larvae. In experiment 1, four MBDs were formulated with different protein sources as follows: MBD 1: herring meal, MBD 2: menhaden meal, MBD 3: menhaden and squid meal; MBD 4: menhaden, squid and herring meal. In experiment 2, four MBDs were formulated as follows: MBD 5: menhaden, squid and herring meal; MBD 6: menhaden, squid, herring and attractants; MBD 7: menhaden, squid, herring and casein, and MBD 8: menhaden, squid, herring, casein and attractants. In experiment 3, three groups were maintained as follows: Group 1: live feed; Group 2: co‐fed with MBD 6; and Group 3: MBD 6. In experiment 1 on 35 dph, survival and body weight (BW) of the fish fed MBD 4 was significantly higher than the MBDs 1 and 2. In experiment 2 on 34 dph, fish fed MBD 6 had significantly higher BW than the commercial microdiets. In experiment 3 on 21 dph, fish receiving only MBD had significantly lower survival than the other groups. Growth, survival and larval fatty acid composition suggested that co‐feeding MBD 6, a mixture of marine protein sources plus attractants was more effective than the other MBDs.     

微颗粒型鱼苗开口饵料的配制及研究进展

综述了近年来微颗粒型鱼苗开口饵料在配方、制备工艺和应用方面所取得的进展,进行了对比分析,指出某些不足之处,重点讨论了微颗粒型鱼苗开口饵料所碰到的营养物渗漏问题,并对今后的发展提出建议。     

不同饵料对海蜇幼体生长、消化酶、抗氧化和免疫酶活力的影响

本研究旨在探讨不同饵料对海蜇(Rhopilema esculentum)幼体生长、消化酶、抗氧化酶和非特异性免疫酶活力的影响.实验设置4个饵料组:小球藻组、虾片(对虾开口饵料)组、卤虫无节幼体组和混合组(卤虫无节幼体和虾片等比例混合),养殖实验持续进行30 d.结果显示:混合组和卤虫无节幼体组海蜇的增重率(WGR)和特...     

饵料卤虫的营养强化对黑斑口虾蛄(Oratosquilla kempi) 幼体消化酶活力及其抗逆性的影响

用扁藻、酵母和"鱼油 酵母"强化3种方式处理的卤虫无节幼体投喂黑斑口虾蛄幼体,对各组黑斑口虾蛄幼体消化酶活力和抗逆性差别分析。结果显示,经过"鱼油 酵母"强化的幼体对氨氮、福尔马林、饥饿和盐度的耐受性均强于对照组。经过扁藻和"鱼油 酵母"强化的第Ⅲ相幼体脂肪酶活力是对照组的3倍,经过酵母和"鱼油 酵母"强化的仔虾蛄幼体脂肪酶活力较高。在第Ⅲ相幼体中淀粉酶活力为扁藻>酵母>对照>"鱼油 酵母"强化,仔虾蛄中酶活力为扁藻>对照>酵母>"鱼油 酵母"强化。在酵母强化第Ⅲ相幼体和对照组仔虾蛄中纤维素酶活力最高。第Ⅲ相幼体对照组的胃蛋白酶和类胰蛋白酶活力均为最高,而"鱼油 酵母"强化仔虾蛄幼体的胃蛋白酶和类胰蛋白酶活力均高于对照组。黑斑口虾蛄幼体消化酶活性和抗逆性能力的变化趋势与其成活率、变态率、生长速度、EPA和DHA含量变化趋势相同,可以作为评价饵料质量好坏的重要指标。     

饲料中不同蛋白含量对斑节对虾幼虾生长及消化酶的影响

选用鱼粉、豆粕和大豆浓缩蛋白为主要蛋白源,配置6个蛋白质水平梯度(36%、38%、40%、42%、44%、46%)的饲料,对斑节对虾幼虾(1.03±0.02 g)进行56 d养殖实验,研究饲料中不同蛋白含量对斑节对虾幼虾生长及消化酶活性的影响。结果表明,(1)摄食40%蛋白饲料的斑节对虾的增重率(417.35%)和特定生长率(2.93%·d-1)获得最大值并显著高于36%蛋白饲料组(P<0.05),但与其它各组无显著差异。饲料蛋白水平在38%时的饲料系数(1.88)最低且与44%和46%蛋白饲料组存在显著性差异(P<0.05)。(2)虾体蛋白含量在44%饲料蛋白组最高,且显著高于36%、38%和42%组(P<0.05)。(3)斑节对虾的蛋白质表观消化率在42%蛋白组最高,44%和46%蛋白饲料组的蛋白质效率显著低于36%～42%蛋白饲料组(P<0.05)。(4)随着蛋白水平的提高,斑节对虾的蛋白酶活性呈现由高到低波动的趋势;淀粉酶活性随着饲料蛋白含量的升高而呈下降趋势,胃淀粉酶活性在38%～42%蛋白饲料组显著高于36%蛋白饲料组(P<0.05),肠淀粉酶活性在42%蛋白饲料组显著高于其它各组(P<0.05)。通过饲料中蛋白质含量与增重率的回归分析,斑节对虾幼虾饲料蛋白的适宜含量为39.70%。     

Growth,partial energy balance,mantle and digestive gland lipid composition of Octopus vulgaris (Cuvier, 1797) fed with two artificial diets

Effects of two binders (gelatine and alginate) were tested on growth, survival, partial energy balance and lipid composition of mantle and digestive gland (DG) of Octopus vulgaris. The three diets tested were given as follows: CON, (Loligo gahi) as control, GEL, composed of squid paste (L. gahi) (300 g kg^?1), fish hydrolyse CPSP^® (100 g kg^?1) and fish meal (500 g kg^?1), agglutinated with 100 g kg^?1 of gelatine and ALG, composed of squid paste (L. gahi) (300 g kg^?1), fish hydrolyse CPSP^® (100 g kg^?1) and fish meal (500 g kg^?1), all agglutinated with 100 g kg^?1 of alginate. Growth rates were 13.7 ± 2.1, 2.1 ± 2.8 and ?2.4 ± 2.9 g kg^?1 bw day^?1, for octopuses fed CON, GEL and ALG diets, respectively. DGs of octopuses had higher concentrations of fatty acids (FA) than the mantle. DG of animals fed CON had higher concentrations of FAs than those fed the artificial diets. Energetic balance demonstrated that physiologically useful energy for maintenance E(B) was affected by type of diet, with negative values of E(B) in animals fed ALG and positive (85 and 154 kJ kg^?1 day^?1) in octopuses fed GEL and CON, respectively. The ALG diet did not cope with the physiological requirements for octopus growth.     

Feeding and digestion in the caridean shrimp larva of Palaemon elegans Rathke and Macrobrachium rosenbergii (De Man) (Crustacea: Palaemonidae) on live and artificial diets

Larvae of two caridean shrimp species, Macrobrachium rosenbergii (De Man) and Palaemon elegans Rathke, were fed live and artificial diets. P. elegans larvae fed exclusively live Artemia salina (15 nauplii mL^?1) developed into first postlarval stage (PL1) within 12 days at a temperature of 25°C and salinity 32.5 g L^?1. Their survival and mean total length at this stage were 88.5% and 6.7 mm respectively. M. rosenbergii larvae fed on 15 Artemia mL^?1 started to metamorphose into PLl within 24 days at 29–30°C and 12 g L^?1. Attempts to completely replace live Artemia for rearing P. elegans during early stages failed, and only a partial replacement was achieved for the larvae of both species. P. elegans larvae survived (49%) solely on a microgranulated diet (Frippak PL diet) from stage zoea (Z) 4–5 to PL1. Similarly, a microencapsulated diet (Frippak CD3) also sustained M. rosenbergii larvae from Z5–6 to PL1 with a 28% survival. Development of the larvae of both species was retarded by 2–3 days and their survivals were lower than those fed on the live diet. The inability of the early larvae of these caridean species to survive on artificial diets is attributed to their undeveloped guts and limited enzymatic capabilities. Trypsin activity in the larvae was determined for all larval stages. It was found that the highest trypsin activity, at stage Z4–5 in P. elegans and at stage Z5–6 in M. rosenbergii, coincides with a rapid increase in the volume of the hepatopancreas and the formation of the filter apparatus. These morphological changes in the gut structure appear to enable the larvae to utilize artificial diets after stage Z5–6. Low larval trypsin activities may be compensated by the easily digestible content of their live prey during early larval stages (Z1–Z4/5) and by longer gastroevacuation time (GET) and almost fully developed guts during later stages.     

Rearing zebrafish (Danio rerio) larvae without live food: evaluation of a commercial, a practical and a purified starter diet on larval performance

Owing to the increasing importance of zebrafish as a vertebrate model in many fields of research, efforts must be made to breed and maintain this species in laboratory. Zebrafish larvae are traditionally reared on cultured live paramecia during the first 9 days of exogenous feeding, followed by a combination of paramecia and artemia nauplii until day 21, making larval rearing expensive, labour intensive and unpredictable. Thus, a trial was conducted with zebrafish larvae in order to evaluate the suitability of artificial diets as an alternative to live food during the first 21 days of exogenous feeding. Five dietary treatments were tested: (1) artemia nauplii; (2) a commercial; (3) a purified; (4) a practical diet, all delivered continuously; (5) the same practical diet delivered manually. The best overall larval performance was achieved in the group fed artemia nauplii (86% survival, 14.3 mm standard length, 46.1 mg wet weight). Compared with existing results obtained with the traditional live food schedule, our results suggest that paramecia might not be the most suitable first food for zebrafish, and that artemia nauplii could be used as the only live food. The present work demonstrates that zebrafish larvae can be reared without live food with a significant growth and a high survival, provided that an appropriate artificial diet is presented in a continuous way. Among the diets tested, the practical diet, if continuously delivered, led to the best performance assuring a mean standard length of 72% of that obtained with artemia and a similar survival rate. Moreover, the purified diet, supporting over 50% survival and an appreciable growth, could be useful in some toxicological studies in which a well‐defined diet is needed.     

Functional palatability enhancer improved growth,intestinal morphology,and hepatopancreas protease activity,replacing squid paste in white shrimp,Litopenaeus vannamei,diets

Squid visceral paste is a popular attractant and feeding stimulator supplement in shrimp feeds in China, but it often faces problems with fluctuating availability, cost, composition, and quality. An 8‐week experiment was performed to test a proprietary palatability enhancer as an alternative to squid paste in white shrimp feed. Seven diets were tested: a control diet with no supplementations; S1 and S3 diets supplemented with squid paste at 1 or 3%, respectively; S1+PE0.1 and S1+PE0.15 supplemented with both 1% squid paste and the palatability enhancer at either 0.1 or 0.15%, respectively; and finally PE0.1 and PE0.15 supplemented only with the palatability enhancer at 0.1 or 0.15%, respectively. The results showed a trend for increased feed intake and weight gain when squid paste was added to the diet compared to the control, but this was worsened by raising the inclusion level from 1 to 3%. The inclusion of the PE, in combination with squid paste or alone at 0.15%, led to a significantly higher growth, and a feeding stimulation effect was also indicated, with PE0.1 and PE0.15 having a higher feed intake than the control. A further beneficial effect was a significant increase in protease activity in the hepatopancreas in the S1+PE0.15, PE0.1, and PE0.15 treatments compared to the control. In addition, a significant increase in the height of the intestinal mucosal folds was observed in PE0.15, followed by PE0.1. The results demonstrated the potential to replace or reduce squid visceral paste in shrimp diets by supplementing with a PE with functional effects beyond feeding stimulation.     

不同饵料搭配对中国明对虾生长和饵料转化效率的影响

采用沙丁鱼肌肉(FF)、鹰爪虾肌肉(SF)、菲律宾蛤仔足肌(CF)、沙蚕(PW)和配合饲料(FD)5种饵料,设计了CF PW、CF FD、PW FD、CF FD PW、FF FD PW FD、FF SF CF PW FD共6种饵料搭配投喂模式,研究了不同饵料搭配对中国明对虾的生长和饵料转化效率的影响。中国明对虾摄食混合饵料后的生长都比除PW处理外的4种单种饵料投喂处理快,CF PW处理的对虾在实验结束时的体重、增重率最大。混合投喂处理的饵料转化效率均高于除PW外的所有单种饵料投喂处理,所有混合投喂处理的实际饵料转化效率都比预测值高,并且除了PW FD和CF FD PW两个处理的实际值与预测值差异不显著外,其它混合处理的饵料转化效率实际值都显著高于预测值。文中还对不同饵料搭配的优势对对虾饵料选择性的影响及产生这些优势的原因进行了探讨。     

Retention efficiency and release of nutrients in the digestive tract of larval shrimp (Penaeus japonicus Bate) using different microencapsulated diets

Retention efficiency and release of the nutrients in the digestive tract of larval shrimp (Penaeus japonicus) using the diets microencapsulated with gelatin and ethyl cellulose respectively were evaluated. The microencapsulated diets were produced using the fluidized bed coating process. 7.8 % gelatin and 4.2 % ethyl cellulose to the whole microencapsulated diet were respectively adopted as coating material. After immersion in 35 ‰ NaCl solution for 1 h, the nitrogen retention efficiency was significantly lower in the diet microencapsulated with gelatin compared with the diet microencapsulated with ethyl cellulose. Free amino acid retention efficiency of the diet microencapsulated with gelatin and ethyl cellulose was 12.9, 17.2 %, respectively. The mysis II larval shrimp (P. japonicus) 10 days after hatch were fed two different microencapsulated diets for 20 days and grew significantly more than the control larval shrimp fed with Artemia and shrimp flake. The nutrient components in intermediate intestine of larval shrimp were increased gradually in the order of the control (50 % shrimp flake + 50 % Artemia), Group I (50 % diet microencapsulated with gelatin + 25 % shrimp flake +25 % Artemia), Group II (100 % diet microencapsulated with gelatin), and Group III (100 % diet microencapsulated with ethyl cellulose). This study confirmed that the microencapsulated diets with slow and controlled release characteristic in the digestive tract of the larval shrimp (P. japonicus).     

Growth and survival rate of three genetic groups fed 28% and 34% protein diets

The strain by nutrition interaction in body weight and survival rate was examined by testing three genetic groups (Selection and Control lines of the GIFT strain, and Red tilapia) at two levels of protein in the diet (28% and 34%). The GIFT strain of Nile tilapia (Oreochromis niloticus) has been selected for high‐breeding values for body weight, whereas the Control was contemporaneously maintained and selected for breeding values of body weight close to the population mean. The Red tilapia (Oreochromis spp) was unselected at the time of the experiment. There were a total of 6000 fish at stocking in the study (2000 fish per genetic group). During the grow‐out period of 147 days, within each genetic group, the fish were randomly assigned to either a 28% or a 34% protein diet. Survival rate during grow‐out averaged 72%. A total of 4335 fish were harvested, with individual body measurements and survival recorded. The effect of genetic group accounted for the largest proportion of variation in body weight and survival, followed by sex and protein level. Across the two dietary protein levels, the GIFT strain had the highest growth. The difference in body weight between the Control and Red tilapia was not statistically significant (P > 0.05). Responses in growth to dietary protein levels also differed between genetic groups. No differences (P > 0.05) in body weight were found in the GIFT selection and Control fish fed 28% or 34% protein diets. However, body weight of Red tilapia was greater in the high‐ than in the low‐protein diet. In contrast to body weight, survival rate from stocking to harvest was affected by protein level. The high‐protein diet significantly improved survival rate, averaging 24% across the three strains. The overall results indicate significant effects of genetic group and dietary protein level on both body weight and survival rate; however, the interaction between strain and dietary protein levels was small and possibly unimportant for these traits. It is concluded that the 28% protein diet used in the selection programme for the GIFT strain results in the selection of genotypes that can perform well under commercial feeds.