Evaluation of optimum dietary vitamin E requirements using DL ‐α‐tocopheryl acetate in the juvenile eel, A nguilla japonica

Summary The study aimed at evaluating the optimum dietary vitamin E requirements using DL ‐α‐tocopheryl acetate in the juvenile eel, A nguilla japonica , as assessed by fish growth performance and fish body composition. Five semi‐purified experimental diets were formulated to contain 0 ( TA 1 ), 15 ( TA 17 ), 30 ( TA 32 ), 60 ( TA 62 ) and 120 ( TA 119  mg  TA  kg −1 diet on a dry matter ( DM ) basis in the form of DL ‐α‐tocopheryl acetate ( TA ). After a 4‐week conditioning period, fish (15 ± 0.3 g) were randomly distributed into aquaria in groups of 20 at 25 ± 1.0°C (mean ±  SD ). One of the five diets was fed on a DM basis to fish in three randomly selected aquaria twice daily to satiation (approximately 3% of wet body weight per day at the beginning and 2% of wet body weight per day at the end of the feeding trial) for 12 weeks. At the end of the 12‐week feeding trial, weight gain ( WG ), specific growth rate ( SGR ), feed efficiency ( FE ) and protein efficiency ratio ( PER ) were determined; these were significantly lower in control fish than in fish fed supplemented diets (P < 0.05). The values for fish fed TA 17 were significantly higher than for fish fed TA 1 , TA 62 or TA 119 (P < 0.05). There were no significant differences in WG , FE or PER among fish that were fed TA 17 and TA 32 , among those that were fed TA 32 and TA 62 , and among those that were fed TA 62 and TA 119 (P > 0.05). There were also no significant differences in SGR among fish fed TA 32 , TA 62 or TA 119 (P > 0.05). A broken‐line regression analysis on the basis of WG , SGR , FE and PER showed that dietary vitamin E requirements of juvenile eels were 21.2, 21.6, 21.2 and 21.5 (mg kg −1 diet), respectively. These results indicate that the dietary vitamin E requirement could be <21.2 mg kg −1 but <21.6 mg kg −1 diet in juvenile eel, A . japonica , when DL ‐α‐tocopheryl acetate is used as the dietary vitamin E source.