Studies On Requirements Of Dietary Methionine, Arginine, Vitamin A, Vitamin E For Turbot (scophthalmus Maximus) Juveniles

Eight-week or twelve-week feeding trials were conducted to investigate the nutritional physiology of methionine, arginine, vitamin A, vitamin E for turbot (Scophthalmus maximus) juveniles. The average initial fish weight in experiments for dietary requirements of methionine and arginine was about 1.80g, and for dietary requirements of vitamin A and vitamin E was 4.43g. The experiments were conducted in indoor flow-through system, water temperature ranged from 17 to 19℃, pH from 7.5 to 7.8, and salinity was 27‰and dissolved oxygen content was approximately 7 mg/L during the experiment. Results of these studies are presented as follows:1. Fish were fed one of six isoenergetic and isonitrogenous experimental diets (D1 - D6) that contained 0.93%,1.14%,1.43%,1.66%,1.92% and 2.26% methionine of dry diet. Following the 12-week feeding trial, there were significant (P< 0.05) diet-related differences in growth and feed utilization for juvenile-turbot. Special growth rate (SGR) and protein efficiency ratio (PER) increased with increasing dietary methionine level up to 1.40% methionine of dry diet (D3), and thereafter, declined. On the contrary, feed conversion ratio (FCR) declined firstly, and then increased. No significant differences were detected in carcass composition besides crude ash, and it was significantly (P< 0.05) higher in D1 treatment than another. Hepatosomatic index (HSI) and condition factor (CF) were not significantly affected by dietary methionine level. On the basis of either SGR or FCR, the optimum dietary methionine requirements of juvenile turbot were estimated to be 1.61% of diet (3.39% of dietary protein) and 1.52% of diet (3.20% of dietary protein), respectively, using second-order polynomial analysis.2. Fish were fed one of five isoenergetic and isonitrogenous experimental diets (Dl-D5) that contained 2.22%,2.66%,3.14%,3.56% and 4.05% arginine of dry diet. Following the 12-week feeding trial, there were significant (P<0.05) diet-related differences in special growth rate (SGR) and serum NOS activity for juvenile turbot. SGR and serum NOS activity increased with increasing dietary arginine level up to 2.66% of diet (D2), and thereafter, declined. However, no significant differences were detected in feed conversion ratio (FCR), protein efficiency ratio (PER) and carcass composition. On the basis of SGR, the optimum dietary arginine requirement of juvenile turbot was estimated to be 3.13% of diet (6.39% of dietary protein), using second-order polynomial analysis.3. Fish were fed one of six isoenergetic and isonitrogenous experimental diets (D1-D6) that contained 1247,2713,6160,8903,11698 and 22155 IU of vitamin A/kg. Following the 8-week feeding trial, there were significant(P<0.05) diet-related differences in special growth rate (SGR), feed conversion ratio (FCR) and protein efficiency ratio (PER) for juvenile turbot, however, no significant differences were detected in survival and carcass composition. SGR increased with increasing dietary vitamin A level up to 2713 IU of vitamin A/kg (D2), and thereafter, level off. FCR and PER were significantly higher in D3 treatment than D1 treatment. Serum AKP activity was significantly (P< 0.05) higher in D5 treatment than another five treatments, however, no significant differences were detected for AKP activity in intestinal brush border membrane vesicles. The vitamin E concentration of liver and serum were significantly (P< 0.05) affected by dietary vitamin E level, and the vitamin E concentrations increased with increasing dietary vitamin A level up to 8903 IU of vitamin A/kg, and thereafter, plateaued. Broken-line regression analysis of liver vitamin E contents showed that juvenile turbot require 104671 IU of vitamin A/kg for maximal liver vitamin E deposition. The results indicated that the optimum level of vitamin A in the diets for juvenile turbot was 2713-104671 IU of vitamin A/kg. 4. Fish were fed one of six isoenergetic and isonitrogenous experimental diets(D1-D6) that contained 26,52,66,132,191 and 339mg of vitamin E/kg. Following the 8-week feeding trial, no significant (P>0.05) diet-related differences were detected in growth, whole body proximate composition. The vitamin E concentration of liver and serum, however, were significantly (P<0.05) affected by the dietary treatment. TBARS of liver and muscle tissue of fish fed elevated dietary vitamin E (≥52 mg vitamin E/kg diet)was significantly lower (P< 0.05)than that noted for fish fed the diet containing no supplemental vitamin E. Fish fed diets containing 66-132mg of vitamin E/kg had significantly increased SOD activity than other treatments in liver. SOD activity in muscle and T-AOC in liver increased significantly according to the increasing vitamin E content of diet. The results indicated that changes in tissue lipid peroxidation measurements precede clinical signs of sub-optimal vitamin E intake and the vitamin E of the diet could promote the antioxidant capacity of juvenile turbot effectively. Based on the liver SOD activity analysis, juvenile turbot require about 66-132mg of vitamin E/kg diet.