Study On Nutrition Physiology Of Zinc, Iron And Copper In Cobia (Rachycentron Canadum)

Feeding experiments were conducted to determine the optimum dietary requirement of zinc, iron and copper for juvenile cobia (Rachycentron canadum) with zinc methionine (ZnMet) as zinc sources, iron sulfate (FeSO4?7H2O) and iron methionine (FeMet) as iron sources, copper sulfate (CuSO4?5H2O) and copper methionine (CuMet) as copper sources, and to compare the bioavailability of the different supplemental sources. Results of the present study are presented as follows:1. The survival rate was not significantly (P>0.05) affected by the different dietary zinc levels. The average weight gain rate (WGR) were significantly(P<0.05)affected by dietary zinc levels, the broken-line regression equation based on WGR showed that the optimum dietary zinc requirement of juvenile cobia was 47.1mg/kg. Whole body moisture and crude protein of the cobia were not affected (P>0.05) by the various levels of dietary zinc. However, fish fed the basal diet had the lowest lipid concentration and highest ash content, and significant differences (P<0.05) were found between the basal diet group and other groups. Serum alkaline phosphatase activities (SAKP) were significantly (P<0.05) affected by different zinc levels in the diet, the broken-line regression equation based on SAKP showed that the optimum dietary zinc requirement of the juvenile cobia was 54.2mg/kg. Therefore, the optimum zinc requirement for juvenile cobia was 47-54mg/kg when zinc methionine (ZnMet) was used as the zinc source.2. The survival rate was not significantly (P>0.05) affected by the different dietary iron levels provided as either FeSO4 or FeMet, however, fish fed the basal diet had the obviously lower survival rate. The weight gain rate (WGR), feed efficiency (FE) and serum catalase activity (SCAT) were both significantly affected (P<0.05) by the different dietary iron levels from two iron sources. The requirements for dietary iron using FeSO4 and FeMet as the supplemental iron sources, determined by broken-line regression analysis, on the basis of WGR were 80.6 mg/kg and 71.3 mg/kg respectively, on FE were 80.5 mg/kg and 71.5 mg/kg and on the activity of SCAT were 94.7mg/kg and 75.1mg/kg. Hemoglobin (Hb) was significantly affected by the various levels of dietary iron, and fish fed the basal diet had the significantly lower hemoglobin levels than fish fed any iron-supplemented diets. Hematocrit (HCT) and Erythrocyte count were not affected by the different iron levels from two iron sources, and the basal dietary group had the lower values. There were no significantly differences (P>0.05) in Whole body moisture and crude protein of the cobia from two iron sources, However, fish fed the basal diet had the lowest lipid concentration and highest ash content. The iron concentration in the whole fish, liver, vertebrae and fillet were not affected by different iron levels from two iron sources, and at every iron level of the diet, liver and vertebral copper concentration was much higher than that of the other tissues. Based on these results, a minimum requirement for dietary iron was recommended to be 80.5-94.7mg/kg from FeSO4, and 71.3-75.1mg/kg from FeMet. This experiment also showed that the bioavailability of FeMet and FeSO4 in juvenile cobia were similar for weight gain rate and feed efficiency, however the relative bioavailability of FeMet is 2.75 times compared with FeSO4 in juvenile cobia for maximum serum catalase activity (SCAT).3. The survival rate was not significantly (P>0.05) affected by the different dietary copper levels provided as either CuSO4 or CuMet, however, fish fed the basal diet had the obviously lower survival rate. The weight gain rate (WGR) and feed efficiency (FE) were both significantly affected (P<0.05) by the different dietary copper levels from two copper sources. The requirements for dietary copper using CuSO4 and CuMet as the supplemental copper sources, determined by broken-line regression analysis, on the basis of WGR were 11.5mg/kg and 8.3mg/kg respectively and on the basis of FE were 11.9mg/kg and 8.2mg/kg. The activity of liver copper zinc-superoxide dismutase (Cu, Zn-SOD) and carcass composition were not significantly affected (P>0.05) by the various levels of dietary copper from two copper sources. The copper concentration in the fillet and plasma were not effected by different copper levels from two copper sources. The copper concentration in the whole fish and vertebrae increased with the increased copper supplementation, and at every copper level of the diet, vertebral copper concentration was much higher than that of the other tissues. Based on these results, a minimum requirement for dietary copper was recommended to be 11.5-11.9 mg/kg from CuSO4, and 8.2-8.3 mg/kg from CuMet. This experiment also showed that the bioavailability of dietary copper with CuMet was approximately 1.5-1.8 times as high as that of CuSO4 to juvenile cobia.