TÓM TẮT NỘI DUNG:

This study was carried out to evaluate the effects of yeasts, K. marxianus on growth performance, feed utilization, immune responses and disease resistances of juvenile tilapia (Oreochromis niloticus). Fish (initial body weight, 6.15g ± 0.10) were randomly distributed into 30 80–L tanks at a stocking density of 20 fish/t ank. One of the experimental diets containing 0.0, 0.03, 0.125, 0.5, 2.0% K. marxianus or 2.0% Saccharomyces cerevisiae was fed to 5 groups of fish to apparent satiation for 10 weeks. At the end of the feeding trial, 10 fish/tank (30 fish/treatment) were challenged with pathogenic Aeromonas hydrophila by oral administration. Mortality was observed twice per day, for 21 days. Although, no significant differences were observed in growth performance and feed utilization among experimental groups, but a trend of higher growth rate was registered in juvenile tilapia fed the yeasts supplemented diets. Non-specific immune responses including serum lysozyme, liver SOD activities of fish were not affected by the yeasts. Cumulative survival of fish post-challenged with A. hydrophila was significantly higher (P < 0.05) in yeasts (K. marxianus or S. cerevisiae) treatments. The present results indicate that dietary supplementation of K. marxianus could improve disease resistances of juvenile tilapia grown from 6.15 to 90 g.