Effectiveness of L-ascorbyl-2-monophosphate Na/Ca as a vitamin C source for yellowtail Seriola quinqueradiata juveniles

A feeding experiment was conducted to examine the efficacy of a vitamin C (L-ascorbic acid, AsA) derivative, L-ascorbyl-2-monophosphate Na/Ca (AMP-Na/Ca) by comparing to L-ascorbyl-2-monophosphate-Mg (AMP-Mg) in terms of growth, AsA content in tissues, and hematology in yellowtail Seriola quinqueradiata juvenile (1.10 +/- 0.01 g). Furthermore, a stress resistance test for the species fed AMP-Na/Ca was also conducted. In experiment 1, 11 test pellet diets with different levels of AMP-Na/Ca (0, 12, 43, 88, 440 and 881 mg AsA kg(-1)diet) and AMP-Mg (0, 16, 52, 106, 595 and 1164 mg AsA kg(-1) diet) were formulated and fed to the yellowtail three times per day for 50 days. In both the vitamin C sources, the survival rates of the fish fed diets without supplemental AsA were lower than 50% at day 20, and more than 50% mortality occurred in fish that fed the diets containing 12 or 16 mg AsA kg(-1) after day 30. However, no significant differences were detected in survival and growth among fish that fed the diets containing more than 43 mg AsA kg(-1). Liver and brain AsA concentrations generally increased with increasing dietary AsA level in both sources. In experiment 2, test diets were formulated to contain 43, 88, 440 and 881 mg AsA kg(-1) using AMP-Na/Ca, and after 60 days of feeding, yellowtail juveniles were subjected to low salinity and air exposure stress. The fish that received diets with 440 mg AsA kg(-1) showed significantly higher tolerance to low salinity stress and higher survival rate in air exposure stress than those of other groups. The present study demonstrated that yellowtail juveniles could utilize AMP-Na/Ca as an AsA source like AMP-Mg, and that supplementation of 43-52 mg AsA kg(-1) diet was optimum for normal growth. However, this study showed that dietary inclusion of 440 mg AsA kg(-1) would be necessary to improve stress resistance of this species.