Effect of water temperature on susceptibility to Streptococcus agalactiae serotype ia infection in nile tilapia (Oreochromis niloticus)

Abstract

Streptococcus agalactiae is one of the causative agents associated with warm-water streptococcosis, in which produce massive mortality in aquaculture. Emergence of disease in tilapia farm usually occurs in high temperature season, which suggested for higher susceptibility of tilapia in this particular condition. Thus, the objective of this study is to investigate the association between water temperature and susceptibility of Nile tilapia (Oreochromis niloticus) to S. agalactiae serotype Ia infection. Nile tilapia were inoculated with 108, 107 or 106 CFU/ml of S. agalactiae serotype Ia field strain via water immersion route and maintained in different water temperature at 25, 30 or 33°C for 1 week. Diseased fish showed typical signs of bacterial septicemia including skin hemorrhage, ascites, kidney enlargement and petechial hemorrhage at liver and brain tissue. Accumulated mortality of tilapia was highest in the group maintained at 33°C followed by 30°C, while at 25°C most of the fish survived and clinical signs were not exhibited. The results from this study suggested that Nile tilapia reared in high water temperature condition susceptible to S. agalactiae via water exposure route.