The ability of Litopenaeus vannamei (initial mean weight: 0.96 ± 0.02 g) to utilize different levels of cornstarch was examined in terms of growth indices, body composition, digestibility and microscopic structure of the hepatopancreas. Six isonitrogenous semipurified diets were fed to satiation to shrimp for 8 weeks in triplicate tanks (30 shrimps per tank) connected to a natural brackish water (6–8 g L−1) recirculating system. Diets contained different levels of cornstarch (100, 150, 200, 250, 300 and 350 g kg−1) as the source of carbohydrate and were balanced using cellulose. Weight gain (WG), survival rate and feed conversion rate (FCR) were considerably affected by cornstarch levels of diets. The highest WG (453.6 g kg−1) and best FCR was observed in shrimp fed the 150 g kg−1 (cornstarch level) diet and was significantly (P < 0.05) higher than those fed diets containing 250–350 g kg−1 cornstarch. However, the survival rate reached maximum in shrimp fed the 100 g kg−1 diet (96.7), some 30% higher than the lowest rate, which was found in shrimp fed the 250 g kg−1 diet. Body lipid tended to be higher in shrimp fed diets with higher cornstarch levels. The apparent digestibility of dry matter and crude fat increased with increasing levels of cornstarch and, hence, decreasing levels of cellulose. In addition, histological study on shrimp fed 10–350 g kg−1 diets exhibited histological changes. The overall conclusion was that the optimum cornstarch level may be set at 100–200 g kg−1 when the diets contain 380 g kg−1 protein.

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This study was conducted to evaluate the effects of dietary thiamin on the physiological status of the juvenile grouper, Epinephelus coioides. Graded levels of thiamin (0.08, 0.50, 2.12, 3.15, 4.63, 12.37 mg thiamin kg -1 diet) were fed to grouper juveniles (mean weight: 16.97 ± 0.14 g) for 10 weeks. Although fish fed the thiamin-deficient (TD) diet showed no obvious symptoms of thiamin deficiency or increased mortality, those fed the lowest doses of thiamin (0.08 and 0.50 mg thiamin kg -1 diet) had significantly decreased transketolase activity in the liver. In addition, the level of liver thiobarbituric acid reactive substances in fish fed the TD diet was 33-67% higher than that in fish with the thiamin-supplemented diet. There were no significant differences in superoxide dismutase activity between the different groups of fish.

An experiment was conducted to investigate the effect of dietary iron supplement on growth, haematology and microelements of juvenile grouper, Epinephelus coioides. Casein-gelatine-based diets supplemented with 0, 50, 100, 150, 200 and 250 mg kg )1 iron from ferrous sulphate were fed to grouper (mean initial weight: 21.0 ± 0.2 g) for 8 weeks. Weight gain was highest in fish fed the diet supplemented with 100 mg kg )1 iron, intermediate in fish fed diets with 50, 150, 200 and 250 mg kg )1 iron and lowest in fish fed the basal diet. Feed efficiency followed a similar trend except that the lowest value was in fish fed the basal diet and the diet supplemented with 250 mg kg )1 iron. Hepatic iron was highest in fish fed diets supplemented with iron ‡100 mg kg )1 , followed by fish fed diet with 50 mg kg )1 iron and lowest in fish fed the basal diet. The whole-body iron was lowest in fish fed the basal diet but not significantly different from other groups, as judged by ANOVA ANOVA. Iron supplement to the basal diet had no significant effect on haematological parameters (red blood cell count, haematocrit and haemoglobin), hepatic copper concentration or manganese, zinc concentration in liver and whole body. Broken-line analysis of hepatic iron indicated that iron supplementation of 100 mg kg )1 satisfied the hepatic iron storage and that further supplementation did not expand the iron status. KEY WORDS

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This study was conducted to evaluate the effects of dietary taurine, as a feed additive, on the hypoxia-tolerance and growth performance of the juvenile grass carp Ctenopharyngodon idellus, one of the most important and intensively cultured freshwater fish, with the largest production in China. Graded levels of taurine (0, 0.5, 1, 1.5, 2 and 2.5 g kg(-1) dry diet) were fed to grass carp juveniles (mean weight: 5.26 ± 0.03 g) for 8 weeks. The survival time during acute hypoxia increased as dietary levels of taurine increased, with the highest dose of taurine resulting in the best acute hypoxia-tolerance. The erythrocyte osmotic fragility in grass carp was significantly improved when dietary taurine level was at least 1.5 g kg(-1) diet and can be improved much more when dietary taurine level was up to 2.5 g kg(-1) diet. A significant correlation between hemolysis rate of the erythrocyte osmotic fragility test and the survival time of acute hypoxia (r = -0.873, P = 0.023 < 0.05) strongly suggested that the biomembrane stabilization function of taurine may contribute to its role of enhancing acute hypoxia-tolerance in grass carp. Dietary taurine cannot improve growth performance of grass carp, but it can increase the value of mesenteric fat index, indicating that dietary taurine influences the lipid metabolism. This study provides valuable information to improve hypoxia-tolerance of grass carp.

This study was conducted to evaluate the effects of dietary riboflavin on antioxidant defense in the juvenile grouper Epinephelus coioides. Graded levels of riboflavin (0.9, 1.6, 4.4, 6.7, 12.9 and 19.4 mg kg(-1) dry diet) were fed to grouper juveniles (mean weight: 14.90 +/- 0.46 g) for 12 weeks. Higher levels of liver thiobarbituric acid reactive substances (TBARS) content were observed in grouper fed low doses (0.9 and 1.6 mg kg(-1) diet) of riboflavin. Both liver glutathione reductase (GR) activity and its activation coefficient (GR-AC) poorly responded to riboflavin deficiency. In addition, other indices of the glutathione-dependent defense system, including the activities of glutathione peroxidase (GSH-PX) and glutathione-S-transferase (GST), and the content of glutathione (GSH), were also non-significantly affected by dietary riboflavin levels. However, the activities of liver superoxide dismutase (SOD) and catalase (CAT) were significantly lower in fish fed 0.9 mg kg(-1) diet, with a positive correlation between the different groups. In conclusion, the present study indicated that the juvenile grouper fed the riboflavin-unsupplemented diet was susceptible to lipid peroxidation (LPO), with lower SOD and CAT activities in the liver. However, the glutathione-dependent defense system of grouper was not affected by dietary riboflavin levels.