Metabolomic responses of Nile tilapia (Oreochromis niloticus) maintained under different temperatures and challenged with Streptococcus agalactiae

Abstract Outbreaks of streptococcosis caused predominantly by Streptococcus agalactiae are a major problem in tilapia culture. Understanding the mechanisms of tilapia infection leading to a high mortality rate at warm temperatures is critical for aquaculture. In this work, gas chromatography–mass spectrometry (GC–MS) coupled with pattern recognition methods and pathway analysis was used to study the metabolic responses in the sera of Nile tilapia (Oreochromis niloticus) induced by S. agalactiae infection at two temperatures. The metabolic profiles showed differences in fish affected by infection raised under different conditions. At 25 °C, a normal temperature for tilapia subsistence, the infection caused changes mainly in energy metabolism, fatty acid composition, and steroid hormone responses, as indicated by 20 corresponding differentially abundant metabolites. At 35 °C, an increased temperature, 27 differentially abundant metabolites identified in infected tilapia compared with those in uninfected tilapia demonstrated more severe and extensive disturbances in energy metabolism and fatty acid metabolism than those at 25 °C. Additionally, the effects of infection also involve enriched carbohydrate-derived structural substances associated with the immune response, but no steroid stress changes were found at high temperature. Metabolites and pathways that were commonly affected by infection at both temperatures indicated that inhibition of glycolysis and consumption of arachidonic acid are more pronounced at high temperature than at normal temperature and might be related to deterioration and death in tilapia. This research provides valuable information for understanding pathogenesis and finding effective methods to control streptococcosis during the warm season.