Location: Aquatic Animal Health Research
Title: Survival, Stress, and Streptococcus Agalactiae Susceptibility in Nile Tilapia, Oreochromis Niloticus, Following Unionized Ammonia Exposure Authors
Submitted to: European Association of Fish Pathologists
Publication Type: Abstract Only
Publication Acceptance Date: May 19, 2005
Publication Date: September 11, 2005
Citation: Evans, J.J., Pasnik, D.J., Brill, G.C., Klesius, P.H. 2005. Survival, stress, and streptococcus agalactiae susceptibility in nile tilapia, oreochromis niloticus, following unionized ammonia exposure. European Association of Fish Pathologists. 12th EAFP International Conference on Diseases of Fish and Shellfish 11th – 16th September 2005 Copenhagen, Denmark. pg 83. Technical Abstract: Elevated unionized ammonia (UIA) has been regarded as a contributory environmental factor in fish disease epizootics. A series of experiments were conducted to determine the toxicity, behavior, blood glucose stress response and disease susceptibility in Nile tilapia Oreochromis niloticus following unionized ammonia exposure. The acute toxicity of unionized ammonia to Nile tilapia was measured in a 96-hour static test. The median lethal concentration (LC50) was 1.46 mg/L UIA at 24 and 48 hours post-exposure, 1.33 mg/L at 72 hours post-exposure, and 0.98 mg/L UIA at 96 hours post-exposure. No mortalities were noted in unexposed (0 mg/L UIA) control fish or fish exposed to 0.5 mg/L UIA. However, 93-100% mortalities were observed within 24 hours among fish exposed to 2.0, 3.0, or 4.0 mg/L UIA. In additional UIA exposure experiments, tilapia were exposed to sub-lethal concentrations of UIA (0.32 to 0.37 mg/L UIA) for 4 or 24 hours and then administered an intraperitoneal injection with 750 colony forming units (CFU) S. agalactiae per fish. Mortalities of UIA exposed and control fish were not significantly different 21 days post-challenge. Blood glucose levels were not significantly different between exposed and control fish at 4 or 24 hours after the beginning of UIA exposure. Glucose levels in both groups increased significantly after bacterial challenge, suggesting that tilapia experienced handling or infection stress but not UIA exposure stress. The results of this study indicate that exposure to increased UIA levels alone had no consistent effect on stress responses in Nile tilapia and that 4 or 24 hour exposure to sub-lethal UIA levels up to 0.37 mg/L do not increase susceptibility to S. agalactiae.