Dietary Chromium Requirement For Grass Carp, Ctenopharyngodon Idellus

The study was conducted to Ctenopharyngodon idellus,the effects of dietary different chromium source and different chromium level on growth,biochemical traits and organ chromium concentration.The contents and results are as follows:1.A growth trial was conducted to investigate the effect of different forms of chromium on growth,haematology parameters and organ chromium concentration of grass carp,Ctenopharyngodon idellus.The forms of chromium were chromium oxides (Cr₂O₃),chromium chloride(CrCl₃),chromium picolinate(CrPic) and chromium nicotinate(CrNic).Five diets supplemented chromium with 0.8 mg/kg diets were fed to triplicate groups of 20 fish(initial weight of 11.35±0.37 g,mean±S.D.) in a flow water system for 10 weeks.Fish fed diets with CrPic and CrNic had significantly improved weight gain,protein efficiency ratio and protein retention of grass carp.Feed conversion for fish fed the diet with CrPic was the lowest,and had significantly lower than Cr₂O₃ and control group.Fish fed diets with Cr₂O₃,CrCl₃,and CrNic had significhanly higher whole body ash contents than control group.The serum glucose concentrations in fish fed CrPic and CrNic were significantly lower than the control group,while liver glucose concentrations were significantly higher.Significantly lower cholesterol concentrations was observed in fish ded diets supplemented with any tape of chromium,and fish fed diets with CrPic and CrNic had significhanly lower cholesterol concentrations than those fed diets with Cr₂O₃,CrCl₃,and control group.The serum LDL-C concentrations in fish fed CrPic was significantly lower than other groups.Fish fed diets with CrPic and CrNic had significhanly higher triglyceride concentrations than those fed diets with Cr₂O₃,CrCl₃, and control group.Serum total protein concentrations in fish fed diets with CrCl₃,CrPic and CrNic were significantly higher than those fed diets with Cr₂O₃ and control group. Serum urea nitrogen concentrations was highest(P＜0.05) for fish fed diets with CrPic, and in fish fed diets with Cr₂O₃,CrCl₃ and CrNic were significantly higher than those fed the diet with control group.Fish fed the diet with CrPic had significantly higher chromium concentrations in kidney than those fed diets with Cr₂O₃ and control group. Liver chromium concentrations in fish fed the diet with CrPic were significantly higher than those fed diets with Cr₂O₃,CrCl₃ and control group.According to WG and liver and kidney chromium concentrations,the appropriate chromium in dietary of grass carp was chromium picolinate.2.A growth trial was conducted to investigate the effect of dietary chromium on growth,haematology paramdters and glucose tolerance in grass carp fingerling, Ctenopharyngodon idella.Fish(average initial body weight=12.78±1.16g) were fed six experimental diets contained chromium at different levels of 0.26,0.48,0.61,0.94, 1.82 and 3.38 mg/kg for 10 weeks.The results showed that fish fed diets supplemented with 0.94 mg Cr/kg had significantly higher specific growth rate,protein efficiency ratio and protein retention,in contrast,feed conversion rate had a significantly lower than control group.Chromium concentrations in whole body increased significantly as dietary chromium levels increased within a range from 0.26 to 0.94 mg/kg and above this,didn't change significantly.Higher liver glycogen was found in fish fed the diet supplemented with 0.48 mg Cr/kg than the fish fed the diet with or without supplementation of chromium,but when the diet with supplementation of chromium raise from 0.61 mg/kg to 3.38 mg/kg,the liver glycogen concentrations decreased.The highest serum insulin concentrations was observed in fish fed the diet supplemented with 0.94 mg Cr/kg,and serum insulin concentrations decreased when the diet supplemented with 1.82 mg Cr/kg to 3.38 mg Cr/kg.There were no significant differences in liver PK and MDH activities for fish fed the diet supplemented with chromium picolinate.Cholesterol concentrations decreased in direct proportion to dietary chromium level and achieved the lowest level when the fish were fed the 0.94 mg Cr/kg,but increased when the fish were fed more than 0.94 mg Cr/kg(P＜0.05).Fish fed the diet supplemented with 0.94 mg Cr/kg had higher triglyceride and high-density lipoprotein cholesterol(HDL-C) concentrations,compared to other treatments.The highest total protein concentrations was observed in fish fed the diet supplemented with 0.94 mg Cr/kg,but total protein concentrations decreased(P＜0.05) when dietary supplementation of chromium was higher than 0.94 mg Cr/kg.The peak values of serum glucose was at 2,3,3,4,3 and 3 h after oral administration when diets with supplementation of chromium raise from 0.26 mg/kg to 3.38 mg/kg.The peak value of serum glucose was most maximal in fish fed the diet supplemented with 0.26 mg Cr/kg,intermediate in fish fed diets supplemented with 0.48～0.61 mg Cr/kg and 1.82～3.38 mg Cr/kg,and most minimal in fish fed the diet supplemented with 0.94 mg Cr/kg. Broken-line regression analysis of SGR and whole body chromium concentrations against dietary chromium level indicated that the chromium requirement of grass carp was 0.83～0.92 mg/kg in our experiment condition.