Studies On Nutritional Physiology Of Copper And Selenium For Juvenile Yellow Croaker Larimichthys Croceus

Two feeding trials were conducted to investigate the nutritional physiology ofcopper and selenium for juvenile large yellow croaker (Larimichthys croceus) infloating sea cages. Furthermore, the optimum dietary copper (Cu) and selenium (Se)requirements for large yellow croaker were determined. The main results are asfollows:1. The CuSO4·5H2O was used as the dietary copper source. Six experimental dietswere formulated to contain the graded levels of copper0(control),1,2,4,8and16mg/kg. The final contents of copper in diets were2.61,3.25,4.65,7.16,11.38, and18.45mg/kg, respectively. Each diet was randomly assigned to triplicate groups of60large yellow croaker juveniles (initial body weight:9.18±0.06g). Fish were fedtwice daily (5:00and17:30) to satiation for10weeks. The results showed that fishfed the basal diet displayed significantly (P<0.05) lower weight gain rate (WGR),copper-zinc superoxide dismutase activity (Cu-Zn SOD), total antioxidant capacity(T-AOC), the whole body and vertebrae Cu concentration. Weight gain rate (WGR),whole body and vertebrae Cu concentration significantly increased with the increasingof dietary copper levels (P<0.05), and thereafter no further increases when the dietaryCu concentration reached4.65,7.16,11.38mg/kg, respectively. However, Cu-ZnSOD activity and T-AOC significantly increased with the increasing of dietary copperlevels and then leveled off (P<0.05), the highest serum Cu-Zn SOD activity andT-AOC were found in the treatment with7.16mg/kg dietary copper, and the highestliver Cu-Zn SOD activity and T-AOC were found in the treatment with4.65mg/kgdietary copper. No significant differences were found in survival rate (SR), feedefficiency (FE), body composition, hepatosomatic index (HSI), viscerosomatic index(VIS) and condition factor (CF)(P>0.05). Analysis by polynomial regression ofserum Cu-Zn SOD activity, the minimum dietary Cu concentration was estimated as7.05mg/kg. Analysis by broken-line regression of WGR, whole body and vertebrae Cu concentration indicate that the optimum dietary Cu concentrations were estimatedas3.41,5.30,5.90mg/kg, respectively.2. The Na2SeO3was used as the dietary selenium source. Six experimental diets wereformulated to contain the graded levels of selenium0(control),0.05,0.2,0.4,0.6and0.9mg/kg. The final contents of selenium in diets were0.08,0.16,0.27,0.44,0.66and0.96mg/kg, respectively. Each diet was randomly assigned to triplicate groups of60large yellow croaker juveniles (initial body weight:9.14±0.09g). Fish were fedtwice daily (5:00and17:30) to satiation for10weeks. The results showed that fishfed the basal diet displayed significantly (P<0.05) lower weight gain rate (WGR),whole body and vertebrae Se concentration. Weight gain rate (WGR), whole body andvertebrae Se concentration significantly increased with the increasing of dietaryselenium levels (P<0.05), and thereafter no further increases when the dietary Seconcentration reached0.27,0.66,0.66mg/kg, respectively. No significant differenceswere found in survival rate (SR), feed efficiency (FE), body composition,hepatosomatic index (HSI), viscerosomatic index (VIS) and condition factor (CF)(P>0.05). The serum glutathione peroxidase (GPX) activity, superoxide dismutase(SOD) activity, total antioxidant capacity (T-AOC) significantly increased with theincreasing of dietary selenium levels (P<0.05), the highest activity were found in thetreatments with0.44,0.44,0.16mg/kg dietary selenium, respectively. The liver GPXactivity, SOD activity, T-AOC, catalase (CAT) activity, glutathione reductase (GR)activity have a similar trend with serum enzyme activity. The liver glutathioneS-transferase (GST) activity significantly reduced with the increasing of dietaryselenium levels (P<0.05), and then increased (P<0.05), the highest activity werefound in the highest Se treatment (0.96mg/kg). Based on WGR, the optimum dietarySe requirement was estimated as0.178mg/kg. Based on the whole body andvertebrae Cu concentration, liver GPX activity, the minimum dietary Seconcentrations were estimated as0.575,0.387,0.440mg/kg, respectively.