Use of probiotics to enhance growth, stimulate immunity and confer disease resistance to Aeromonas salmonicida in rainbow trout (Oncorhynchus mykiss)

An 8-week feeding trial was conducted to evaluate the effects of dietary probiotics on growth, nonspecific immune responses and disease resistance in juvenile rainbow trout, Oncorhynchus mykiss. Fish averaging 5.8 +/- 0.8 g (mean +/- SD) were fed one of the five experimental diets; one control (Cont), and four other diets were prepared by supplementing single probiotics 1 (Bacillus subtilis; SP1, 0.5%), single probiotics 2 (Bacillus licheniformis; SP2, 0.5%), multi-probiotics (B. subtilis + B. licheniformis; MP, 0.5%) and oxytetracycline (OTC) at 5 g OTC kg(-1) diet. After 8 weeks of the feeding trial, weight gain and specific growth rate of fish fed SP1, SP2 and OTC diets were significantly higher than those of fish fed Cont diet (P < 0.05). Superoxide dismutase (SOD) and lysozyme activities of fish fed SP1, SP2 and MP diets were significantly higher than those of fish fed Cont diet (P < 0.05). There were no significant differences in SOD and lysozyme activities among fish fed SP1, SP2, MP and OTC diets. In challenge test with Aeromonas salmonicida for 15 days, fish fed SP1, SP2 and MP diets showed significantly higher cumulative survival rate than those of fish fed Cont diet (P < 0.05). However, there were no significant differences in cumulative survival rate among fish fed SP1, SP2, MP and OTC diets. Although there was a little advantage in fish fed MP diet in terms of non-specific immune responses, single or multi-probiotics are equally effective statistically. These results indicate that single or multi-probiotics had equal beneficial effects as an antibiotic replacer on growth performance, non-specific immune responses and disease resistance in juvenile rainbow trout.