An eight-week feeding trial was conducted to evaluate the effects of different dietary probiotic supplements in juvenile whiteleg shrimp, Litopenaeus vannamei. A basal control diet without probiotics (CON), and five other diets by supplementing Bacillus subtilis at 10⁷ CFU/g diet (BS₇), B. subtilis (BS₈), Pediococcus pentosaceus (PP₈), and Lactococcus lactis (LL₈) at 10⁸ CFU/g diet, and oxytetracycline (OTC) at 4 g/kg diet were used. Whiteleg shrimp with initial body weights of 1.41 ± 0.05 g (mean ± SD) were fed with these diets. Growth of shrimp fed BS₈ and LL₈ diets was significantly higher than those of shrimp fed the CON diet (p < 0.05). Superoxide dismutase activity in shrimp fed PP₈ and LL₈ diets was significantly higher than that of shrimp fed the CON diet (p < 0.05). Lysozyme activity of shrimp fed probiotics and OTC diets significantly improved compared to those on the CON diet (p < 0.05). The intestinal histology showed healthier guts for shrimp fed the probiotic diets (p < 0.05). Immune-related gene expression in shrimp fed BS₈, PP₈ and LL₈ diets was recorded as significantly higher than that of shrimp fed CON and OTC diets (p < 0.05). Also, results of the challenge test for 7 days and the digestive enzyme activity of shrimp fed BS₈, PP₈, and LL₈ were significantly improved compared to those on the CON diet (p < 0.05). Therefore, these results indicated that L. lactis at 10⁸ CFU/g could be an ideal probiotic for whiteleg shrimp, and also B. subtilis WB60 and P. pentosaceus at 10⁸ CFU/g could improve the growth, immunity, histology, gene expression, digestive enzyme activity, and disease resistance, while replacing antibiotics.

An eight-week feeding trial was conducted to evaluate the effects of a basal control diet (CON), Bacillus subtilis at 10⁷ (BS₇) and at 10⁸ CFU/g diet (BS₈), Lactococcus lactis at 10⁷ CFU/g (LL₇) and at 10⁸ CFU/g diet (LL₈), and oxytetracycline (OTC) at 4 g/kg diet on Nile tilapia. Fish with initial body weight of 2.83 ± 0.05 g (mean ± SD) were fed two times a day. Weight gain, specific growth rate, feed efficiency, protein efficiency ratio and lysozyme activity of fish fed BS₈, LL₈ and LL₇ diets were significantly higher than those of fish fed CON diet (p < 0.05). Superoxide dismutase and myeloperoxidase activity of fish fed BS₈, LL_8, BS₇, LL₇ and OTC diets were significantly higher than those of fish fed CON diet. Intestinal villi length and muscular layer thickness of fish fed BS₈, LL₈ and LL₇ diets were significantly higher than those of fish fed CON and OTC diets. Also, heat shock protein 70 (HSP70), interleukin (IL-1β), interferon-gamma (IFN-γ) and tumour necrosis factor (TNF-α) gene expression of fish fed BS₈ and LL₈ diets were significantly higher than those of fish fed CON diet. After 13 days of challenge test, cumulative survival rate of fish fed BS₈ and LL₈ diets were significantly higher than those of fish fed CON, BS₇ and OTC diets. Based on these results, B. subtilis and L. lactis at 10⁸ (CFU/g) could replace antibiotics, and have beneficial effects on growth, immunity, histology, gene expression, and disease resistance in Nile tilapia.