Effects of dietary propolis supplementation on growth performance, immune responses, disease resistance and body composition of juvenile eel, Anguilla japonica

This study was conducted to investigate the effects of dietary propolis supplementation on growth performance, immune responses, disease resistance and body composition of juvenile eel, Anguilla japonica, in order to evaluate its bioavailability as a feed additive for this species. A total of 540 fish averaging 7.7 ± 0.22 g (mean ± SD) were randomly distributed into 18 tanks in groups of 30, and each tank was then randomly assigned to one of three replicates of six diets containing 0 (P0), 0.25 (P0.25), 0.5 (P0.5), 1.0 (P1), 2.0 (P2) and 4.0 (P4) % dietary propolis. At the end of 12 weeks of feeding trial, weight gain (WG), specific growth rate (SGR), feed efficiency (FE) and protein efficiency ratio (PER) of fish fed P0.5 diet were significantly higher than those of fish fed P0, P1, P2 and P4 diets (P < 0.05). These parameters were 148.9%, 0.72% day−1, 94.4% and 2.9, respectively for fish fed P0.5 diet. Serum lysozyme activity of fish fed P0.5 (105.7 units mL−1) and P1 (106.0 units mL−1) diets were significantly higher than those of fish fed P0, P0.25, P2 and P4 diets. Mucus lysozyme activity of fish fed P1 (8.4 units 10 cm−2) diet was significantly higher than those of fish fed P0, P2 and P4 diets. Results indicated that the optimum dietary propolis supplementation levels could be 0.25–0.5% for optimum growth and feed efficiency, and 0.5–1% for enhanced immune responses and disease resistance in eel, A. japonica. This study may suggest that the dietary propolis level for the optimum immune responses could be higher than the level for the optimum growth of eel.