The enrichment of diet with beneficial bacteria (single- or multi- strain) in biofloc system enhanced the water quality, growth performance, immune responses, and disease resistance of Nile tilapia (Oreochromis niloticus)

The present study examined the influences of dietary single strain (SSP; Lactobacillus plantarum) or multi-strain (MSP; Bacillus subtilis, L. plantarum, L. rhamnosus, L. acidophilus, L. delbrueckii) potential probiotics on Nile tilapia (Oreochromis niloticus) in biofloc (BF) and stagnant-renewal (SR) culture systems. Fish (8.63 ? 3.35 g) were allotted in six groups: T1, SR control; T2, SR + SSP; T3, SR + MSP; T4, BF + MSP; T5, BF + SSP; T6, BF control. After 112 days, water dissolved oxygen (O2), pH, electrical conductivity (EC), total dissolved solids (TDS), total suspended solids (TSS), total ammonia nitrogen (TAN), un-ionized ammonia (NH3), and nitrite (NO2) levels were significantly increased while nitrate (NO3) concentrations were decreased under BF condition. Also, bacterial supplements showed significant effects on EC, TAN, NH3, NO2, and NO3 levels. The BF availability remarkably enhanced the activities of digestive enzymes and fish fed SSP-containing diet presented significantly superior weight gain and average daily growth over other diets. A significant effect on amylase activity was detected by probiotic and culture system interactions. Meanwhile, serum total protein, albumin, globulin, total immunoglobulin, superoxide dismutase (SOD), myeloperoxidase (MPO), and respiratory burst activity (RBA) were significantly higher and malondialdehyde and endotoxin were lower for fish stocked in BF system. Additionally, MSP-containing diet significantly promoted serum protease, SOD, catalase (CAT), alkaline phosphatase (AP), MPO, and RBA activities compared to other tested diets. Interestingly, serum alternative complement (ACH50) and lysozyme activities were merely affected by the main effect of probiotics. However, probiotics and culture system found to have individual or combined effects on the intestinal antioxidant enzymes, AP, and proinflammatory cytokines (tumor necrosis factor alpha and interleukin-1 beta). Further, tilapia challenged with Aeromonas hydrophila showed reduced mortality in BF groups fed probiotics. The results suggested that the effect of probiotics greatly differed upon the culture condition and the application of multiple strains probiotics had higher efficiency toward immunity than single strain probiotic.