Dietary vitamin C improves the quality of yellowtail ( Seriola quinqueradiata) seedlings

Several parameters were investigated to determine the effects of vitamin C (AsA) on improvement of juvenile yellowtail quality for restocking. The dry pellets with different levels of l-ascorbyl-2-phosphate-Mg (APM) (0, 400, 1000, and 2000 mg/kg diet) were formulated and fed to 500 juveniles (mean total length (TL): 3.6 cm) per treatment with duplicate tanks (500 l round type). Test diets were fed three times a day at 25°C water temperature for 20 days. After the 20-day trial, 10 to 20 juveniles from each treatment group were randomly sampled for a test of `air dive' and schooling behavior. The `air dive' was conducted to determine the number of survivors after exposure to air while the schooling behavior such as schooling pattern, swimming activity and individual distance were recorded using the video system and analyzed by the computer graphic system. Survival was over 90% and there was no sign of AsA deficiency in any group during the 20-day trial. There was no effect of APM intake on growth. Liver AsA increased with increasing APM intake whereas that of brain AsA levelled off at 1000 mg APM. The tolerance against air exposure seemed poor in fish fed on APM-free diet although statistical significance was not detected ( P>0.05). The schooling rate was significantly higher in fish fed on diets containing 1000 or 2000 mg APM. It is speculated that juvenile yellowtail fed on diet containing more than 1000 mg APM would be able to show better growth and survival under natural conditions after release.