Growth performance and starch utilization in common carp (Cyprinus carpio L.) in response to dietary chromium chloride supplementation

A nutrition trial was conducted on juvenile common carp (Cyprinus carpio), initial mean body weight 15 +/- 0.4 g within a controlled facility at 25 +/- 0.5 degrees C. Six diets containing various levels of supplementary Cr (0, 0.2, 0.5, 1.0, 1.5, and 2.0) mg Cr/kg of diet as Cr chloride hexahydrate were fed to carp for a period of 10 weeks. Lower growth performance was observed in fish fed on the control diet and the diet supplemented with the highest level of Cr (2.0 mg Cr/kg). Although fish fed 0.5 mg Cr/kg showed the best growth performance, this was not significantly different (P > 0.05) from fish fed 1.0 mg Cr/kg. The regression of plasma glucose concentration was linear (R-2 = 0.97 and P value = 0.001) as the Cr content of the diet increased (up to 1.5 mg Cr/kg). Cr carcass content was elevated with an increasing level of dietary Cr supplementation up to 1.5 mg Cr/kg; but fish fed on the diet supplemented with the highest level of Cr (2.0 mg Cr/kg) showed a decrease in Cr carcass content. Histological examination to evaluate the impact of different Cr supplementation on liver and gut tissues showed notable changes. The higher level of Cr (2.0 mg Cr/kg) in the diet gave rise to elevated hepatocyte vacuolization and changes in gut tissue morphology. It appeared that Cr chloride significantly improved growth within a defined range (0.2-1.5) mg Cr/kg without any negative impact, while 2.0 mg Cr/kg in carp diet seems to be the threshold for the initiation of toxicity. (C) 2012 Elsevier GmbH. All rights reserved.