Weaning of Atlantic halibut Hippoglossus hippoglossus L. using formulated diets with various levels of ascorbic acid

Atlantic halibut larvae (120 mg) were weaned to formulated diets with diffe rent supplementations of ascorbate-poly-phosphate, ApP (300, 2000 and 3000 mg ascorbic acid (AA) equivalents kg(-1) diet). The experiment lasted for 5 0 days with cofeeding of enriched Artemia and formulated diets during the f irst 30 days. During the last 20 days, only formulated diets were offered t o the fish. One control group was fed only Artemia (770 mg AA kg(-1) dry we ight) during the entire experimental period. The specific growth rate durin g the 50 days was approximate to 4.5% day(-1) and the mean weights in all d ietary groups were approximate to 1 g when the experiment was terminated. N o differences in mean weight and mortality were observed between the groups fed formulated diets and that fed Artemia during the experiment. The fish size in the groups fed formulated diets ranged between 0.10 and 3.05 g and this differed from the Artemia group where the size ranged between 0.35 and 1.35 g. Dietary levels of ApP had no positive effect on growth and surviva l. The retention of AA was significantly higher in the groups fed high diet ary levels of ApP. Apparently, the bioavailability of high dietary levels o f ApP appeared to be low for young halibut. After stressing the fish using a high-salinity challenge test, no significant difference in survival occur red among the dietary groups. Cortisol levels in plasma recorded 3 h post s tress was significant lower in the Artemia group compared with the groups f ed the formulated diets.