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 whichproduce massive mortality in aquaculture. Emergence of disease in tilapia farm usually occurs in high temperatureseason, which suggested for higher susceptibility of tilapia in this particular condition. Thus, the objective of thisstudy is to investigate the association between water temperature and susceptibility of Nile tilapia (Oreochromisniloticus) to S. agalactiae serotype Ia infection. Nile tilapia were inoculated with 108, 107 or 106 CFU/ml of S. agalactiaeserotype Ia field strain via water immersion route and maintained in different water temperature at 25, 30 or 33oC for1 week. Diseased fish showed typical signs of bacterial septicemia including skin hemorrhage, ascites, kidneyenlargement and petechial hemorrhage at liver and brain tissue. Accumulated mortality of tilapia was highest in thegroup maintained at 33oC followed by 30oC, while at 25oC most of the fish survived and clinical signs were notexhibited. The results from this study suggested that Nile tilapia reared in high water temperature conditionsusceptible to S. agalactiae via water exposure route.