No abstract

A feeding experiment was conducted to determine the optimum dietary level of ascorbic acid (AsA) for Japanese eel juveniles using L‐ascorbic acid Ca based on growth, AsA content in tissues, hematology, and bactericidal activity of serum with Escherichia coli. Test diets with six levels of AsA (3, 10, 27,126, 645, and 3,135‐mg/kg diet) as Ca ascorbate were fed to juvenile Japanese eels (11.0 ± 0.2 g) once a day for 8 wk. High survival rates (> 80%) were observed among all dietary treatment groups. The specific growth rates of the fish fed diets containing 3 and 10‐mg AsA/kg were significantly (P < 0.05) lower than those of other groups. Liver and brain AsA contents of the fish fed diets containing 3, 10, and 27‐mg AsA/kg were significantly (P < 0.05) lower than those of the fish fed diets containing 645 and 3,135‐mg AsA/kg. Hemoglobin content tended to be higher in the fish fed diets containing 645 and 3,135‐mg AsA/kg than those of the fish fed other diets. Hematocrit value and total serum protein content of the fish fed diets containing 645 and 3135 mg AsA/kg were significantly (P < 0.05) higher than those of the other groups. The fish fed diets containing more than 27‐mg AsAlkg showed a higher bactericidal activity of serum than the fish fed the diets containing 3‐mg and 10‐mg AsA/kg. The optimum dietary level of AsA for the Japanese eel juveniles growth was estimated to be more than 27‐mg AsA/kg. Furthermore, the inclusion of 645‐mg AsA/kg or more also increased the hematocrit, hemoglobin, total serum protein value, and liver and brain vitamin C concentrations.

l‐ascorbyl‐2‐monophosphate‐Na/Ca (AMP‐Na/Ca) was used as a vitamin C source to investigate the ascorbic acid (AsA) requirements on growth performance and stress resistance of the post‐larval kuruma shrimp, Marsupenaeus japonicus. Purified carrageenan‐microbound diets with six levels of AMP‐Na/Ca, AsA equivalent to 0, 20, 56, 87, 759 and 1697 mg kg−1 diet were fed to triplicate groups of M. japonicus (mean initial weight 16±0.3 mg) for 30 days. The diets with AsA 0, 20 and 56 mg kg−1 showed high cumulative mortality after 10 days of feeding. After the 30‐day trial, the shrimp fed these diets had significantly lower survival and weight gain (WG, %) than those fed the 87, 759 and 1697 mg AsA kg−1 diets. Specific growth rate and individual dry weight showed the same pattern as WG (%). There were no significant differences in growth performance among the groups fed the AsA levels at 87, 759 and 1697 mg kg−1 at the termination of feeding trial. Broken‐line regression analysis indicated that 91.8 mg AsA kg−1 in the diet was the optimum for post‐larval shrimp. On the other hand, dietary level of more than 800 mg AsA kg−1 was needed to ensure high resistance to stressful conditions such as osmotic and formalin stressors.