Effects of dietary non-viable Bacillus sp. SJ-10, Lactobacillus plantarum, and their combination on growth, humoral and cellular immunity, and streptococcosis resistance in olive flounder (Paralichthys olivaceus).

Heat-killed (HK) Bacillus sp. SJ-10 (B), HK Lactobacillus plantarum (P), and their combination were dietary supplemented to olive flounder (Paralichthys olivaceus) to quantify the effects on growth, innate immunity, and disease resistance. Four test diets were supplied: a control feed free of HK probiotics, 1 × 10 CFUs g single treatments of each of HK B (HKB) and HK P (HKP), and an equal proportion of (0.5 HKB + 0.5 HKP) × 10 CFUs g (HKB HKP). At 8 weeks of completion feeding trail, HKB HKP significantly (P < .05) improved growth, feed utilization, and nonspecific immune parameters (respiratory burst and superoxide dismutase) compared to the control group. Similarly, serum lysozyme and myeloperoxidase activities were higher in both HKB and HKBHKP groups. The levels of pro-inflammatory cytokine IL-6 in the liver and IL-1β in the liver, kidney, and spleen were also improved in the treatments, but microvilli length was only increased in HKBHKP. After Streptococcus iniae 1 × 10 CFUs mL challenged; HKB and HKBHKP had a higher survival than control and HKP. Overall, dietary administration of synergy HK probiotics elevated growth, cellular and humoral immunity, and streptococcosis resistance in olive flounder.