Probiotic effects of Aspergillus oryzae on the oxidative status, heat shock protein, and immune related gene expression of Nile tilapia (Oreochromis niloticus) under hypoxia challenge

Abstract

This trial was undertaken to assess the probiotic potential of Aspergillus oryzae (ASP) on the oxidative status, heat shock protein, and immune-related gene expression of Nile tilapia under hypoxia challenge. For 60 days fish were fed the control diet, or two diets incorporated with ASP at 1 × 106 or 1 × 108 CFU g-1 (control, ASP1, and ASP2) and were then exposed to hypoxia challenge. After 60 days, fish fed ASP1 or ASP2 exhibited significant improvements in growth performance and feed efficiency (P < 0.05). Before and after hypoxia challenge, decreased glucose and cortisol levels were also recorded in the group supplemented with the ASP probiotic. Further, ASP effectively increased the antioxidative enzymes activity (SOD and GPX) with lower malondialdehyde (MDA) in tilapia before and after hypoxia stress. The blood antibacterial capacity (bactericidal and phagocytosis activity) against Aeromonas hydrophila was significantly (P < 0.05) increased by ASP before and after hypoxia stress. Furthermore, ASP supplementation significantly enhanced total serum protein, nitro blue tetrazolium, immunoglobulin M, and lysozyme activity, which indicated the immunomodulation imparted by the ASP in fish under hypoxia stress (P < 0.05). Relative messenger RNA of TNF-α, IL-1β, and HSP70 gene expressions were upregulated in fish fed on ASP compared with the control before and after hypoxia stress. Thus, we conclude that the use of ASP significantly improves defense against hypoxia stress in Nile tilapia.