Quorum quenching probiotics modulated digestive enzymes activity, growth performance, gut microflora, haemato-biochemical parameters and resistance against Vibrio harveyi in Asian seabass (Lates calcarifer)

Abstract

The use of probiotics is a promising and increasingly common strategy to maintain a healthy farming environment in an eco-friendly and sustainable manner. The goal of this study was to investigate the possible effects of dietary supplementation with autochthonous quorum quenching (QQ) probiotics on growth, digestive enzymes activity, haemato-biochemical responses, gut microbial communities and resistance against Vibrio harveyi in Asian seabass. Asian seabass (75 ± 0.6 g and 15.5 ± 0.3 cm) were fed with basal diet (control groups) and basal diet containing 1 × 109 CFU per g Bacillus thuringiensis QQ1 or Bacillus cereus QQ2 for 6 weeks. Feeding with diets supplemented with QQ probiotics for 35 days (pre-infection period) resulted in a significant (p < 0.05) alteration of the growth parameters (RGR, FCR, SGR, PER, FER and FI) and digestive enzymes activity (α-amylase, total protease, lipase, trypsin, alkaline phosphatase, T/C and A/T). Hematocrit (Hct) and total leucocyte count (TLC) were significantly (p < 0.05) elevated in fish fed with QQ1. Respiratory burst activity (RBA) likewise significantly (p < 0.05) increased in the probiotic groups relative to the control groups. Moreover, a significant decrease (p < 0.05) in the level of serum total cholesterol was observed in fish fed with probiotic. QQ1 and QQ2 were able to colonize the host's intestine at high number after 5 weeks. Hct and RBA in QQ1 and QQ2, globulin in QQ2 and TLC in QQ1 were significantly (p < 0.05) promoted compared to the positive control (PC) after infection with Vibrio harveyi (day 42). Serum triglycerides, cholesterol, alkaline phosphatase (ALP), alanine aminotransferase (ALAT), aspartate aminotransferase (ASAT) and lactate dehydrogenase (LDH) were significantly (p < 0.05) lower in the probiotic treatments than the PC group after infection. QQ probionts significantly (p < 0.05) improved the cumulative survival of Asian seabass against V. harveyi. According to these findings, we suggest that B. cereus QQ2 and particularly B. thuringiensis QQ1 have a high potential to enhance the performances of Asian seabass and therefore can be effectively applied for the control of V. harveyi.