No synergistic effects by the dietary supplementation of ascorbic acid, alpha-tocopheryl acetate and selenium on the growth performance and challenge test of Edwardsiella tarda in fingerling Nile tilapia, Oreochromis niloticus L.

摘要

To investigate the potential synergistic effects of dietary ascorbic acid (AA), alpha-tocopheryl acetate (TA) and selenium (Se) supplementation above minimum requirement levels on the growth performance and disease challenge of fingerling Nile tilapia, Oreochromis niloticus L., five experimental diets were formulated: control (150 mg AA, 100 mg TA and 0.2 mg Se per kg diet), excessive ascorbic acid (eAA) (2000 mg AA, 100 mg TA and 0.2 mg Se per kg diet), excessive alpha-tocopheryl acetate (eTA) (150 mg AA, 240 mg TA and 0.2 mg Se per kg diet), excessive selenium (eSe) (150 mg AA, 100 mg TA and 0.5 mg Se per kg diet) and excessive all (eALL) (2000 mg AA, 240 mg TA and 0.5 mg Se per kg diet). Experimental fish averaging 2.9 were randomly distributed in each aquarium as a group of 40 fish with total weight 116 +/- 2.9 g (mean +/- SD). Each diet was fed on a dry-matter basis to fish in three randomly selected aquaria at a rate of 4-8% of total body weight daily After 10 weeks of the feeding trial, fish fed eAA, OTA and e]ALL diets had significantly higher weight gain, feed efficiency ratio, protein efficiency ratio and specific growth rate than fish fed eSe and control diets (P < 0.05). There was no significant difference among fish fed five experimental diets in cumulative mortalities when fish were challenged with Edwardsiella tarda at the end of the experimental period. These results indicate that sufficient supplementation of dietary AA or TA had positive effects on growth performance, but there was no synergistic effect of excessive dietary AA, TA and Se supplementation on growth performance and disease resistance to F. tarda in fingerling Nile tilapia.