The effect of dietary organic chromium on specific growth rate, tissue chromium concentrations, enzyme activities and histology in common carp, Cyprinus carpio L.

A 63-day feeding trial was carried out to investigate the effect of three levels of Cr yeast (0.5, 1.0 and 2.0 mg Cr/kg) on the utilization of diets containing 38.5 % of maize starch or dextrin in common carp, Cyprinus carpio L. (initial mean body mass 14 ± 0.3 g) in an auto circulator system at 25 ± 0.5 °C. A two-way analysis of variance (ANOVA) showed that the final body mass (FBM), percentage mass gain (%MG), specific growth rate (SGR) and feed conversion ratio (FCR) were significantly (P < 0.05) affected by the two sources of variation (carbohydrate source and Cr level). In general, fish fed on a diet containing starch and fortified with 0.5 mg Cr/kg performed significantly higher FBM (47.23 g), %MG (225.11), SGR (1.91) and lower value of FCR (1.24) compared to fish fed on the other diets. Carp fed on 2.0 mg Cr/kg with maize starch and 1.0 mg Cr/kg with dextrin-based diet showed a significant reduction (P < 0.05) in whole body lipid content as confirmed by a two-way ANOVA. Fish fed on a maize starch-based diet supplemented with 0.5 and 1.0 mg Cr/kg recorded the highest activities for hexokinase enzyme. Glucose-6-phosphate dehydrogenase activity was neither affected by Cr concentration nor by dietary carbohydrate source. Fish fed on dextrin-based diets accumulated higher Cr in the whole tissue compared to fish fed on starch-based diets. Normal histological structures in the liver and gut tissues were observed in all groups. The present data clearly showed that dietary Cr yeast was safe in the fish diet at the levels tested.