Effects of Dietary Non-Viable Bacillus sp. SJ-10, Lactobacillus plantarum and Their Combination on Growth, Humoral and Cellular Immunity, and Streptococcosis Appraisal in Olive Flounder (Paralichthys olivaceus)

Abstract

Single strain of heat killed (HK) Bacillus sp. SJ-10 (B), HK Lactobacillus plantarum (P) and their combinations were dietary administered to olive flounder (Paralichthys olivaceus) to quantify effects on growth, innate immunity, and disease resistance. Among four categories of test diets, control feed was free from any kind HK probiotics, and treatments were incorporated with 1×108 CFU g –1 of each HK BSJ-10 (HKB) and HK LP (HKP) as well as equal proportion of (0.5 HKB + 0.5 HKP) ×108 CFU g –1 (HKB0.5 HKP0.5). After 8 weeks feeding, synergy of single probiotics (HKB0.5 HKP0.5) significantly (P < 0.05) improved growth (FBW, WG, SGR) and feed utilizations (FCR and PER) parameters compared to control group. For nonspecific immunity, HKB0.5HKP0.5 evolved alteration of respiratory burst and superoxide dismutase activities relative to control, HKB, and HKP. Serum lysozyme and myeloperoxidase activity was higher in both HKB and HKB0.5HKP0.5, compared to control. Serum biochemical parameters ALT and AST indicated no changes in any test diets but total cholesterol and glucose were higher in HKB0.5HKP0.5 versus control. Pro-inflammatory cytokine TNF-α in the kidney was significantly amplified with mix HK probiotic compared to control and other individual treatments. IL-6 in the liver as well as IL-1β in the liver, kidney and spleen was also improved in HKB groups. No differences were identified in the microvilli length among the groups but HKB0.5HKP0.5 demonstrated numerically elevated length. Fish when subjected to disease challenge with 1 ×108 CFU mL–1 Streptococcus iniae, HKB and HKB0.5HKP0.5 fed fishes showed higher survival rate than control and HKP group. Therefore, dietary HK probiotics combination administration elevates growth, cellular and humoral immunity, and streptococcosis resistance in olive flounder.