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°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 (2.0mg Cr/kg). Although fish fed 0.5mg Cr/kg showed the best growth performance, this was not significantly different (P>0.05) from fish fed 1.0mg 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 1.5mg Cr/kg). Cr carcass content was elevated with an increasing level of dietary Cr supplementation up to 1.5mg Cr/kg; but fish fed on the diet supplemented with the highest level of Cr (2.0mg 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 (2.0mg 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 2.0mg Cr/kg in carp diet seems to be the threshold for the initiation of toxicity.

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.

The efficacy of chromium as a growth enhancer for mirror carp (Cyprinus carpio L): an integrated study using biochemical, genetic, and histological responses.

A growth trial was conducted on juvenile mirror carp (Cyprinus carpio L.) for 8 weeks to compare the efficacy of three chromium (Cr) compounds (Cr chloride, Cr picolinate, and Cr yeast) at a level 0.5 mg/kg as a potential growth enhancer. In addition, a high level of Cr (2.0 mg/kg) as Cr chloride has also been added in parallel for comparison. All Cr fortified diets at a level 0.5 mg/kg produced superior growth for carp compared to the control group and the group fed the high level of Cr chloride (2.0 mg/kg). Metabolic indicators measured included two of the key liver enzymes (hexokinase, HK) and (glucose-6-phosphate dehydrogenase, G6PD) activity. The results validated the positive effect of Cr at a level 0.5 mg/kg on enzyme activity and carbohydrate utilization producing significantly better growth performance for mirror carp. The study also included measurement of DNA strand breaks in the erythrocytes using the comet assay which revealed significantly (P < 0.05) increased DNA damage in fish fed on high level of Cr chloride (2.0 mg/kg) but the other treatments were not significantly different (P > 0.05) from the control groups. The concentration of Cr in the liver, gut, and whole fish tissues increased with increasing dietary Cr supplementation. Overall, Cr supplementation at a level 0.5 mg/kg from different sources may affect growth performance in carp by activation of some key liver enzymes (HK and G6PD).