ARS | Publication request: TOXICITY, STRESS RESPONSES, AND DISEASE SUSCEPTIBILITY IN NILE TILAPIA, OREOCHROMIS NILOTICUS, EXPOSED TO UNIONIZED AMMONIA

Submitted to: American Fisheries Society Transaction
Publication Type: Abstract Only
Publication Acceptance Date: July 15, 2005
Publication Date: July 27, 2005
Citation: Pasnik, D.J., Evans, J.J., Klesius, P.H., Brill, G.C. 2005. Toxicity, stress responses, and disease susceptibility in nile tilapia, oreochromis niloticus, exposed to unionized ammonia. 2005 Annual Meeting of the Fish Health Section/American Fisheries Society Transaction. Minneapolis, MN July 27-29, 2005. Abstract p. 37.

Technical Abstract: Unionized ammonia (UIA) is a well-known aquatic pollutant and toxin of fish, and sublethal UIA concentrations have been shown to cause negative behavioral, physiological, histologic, and immunologic changes in some species of fish. Experiments were conducted to determine the behavior responses, median lethal concentration (LC50), blood glucose stress responses, and disease susceptibility in Nile tilapia, Oreochromis niloticus, following UIA exposure. The acute toxicity of UIA to Nile tilapia was measured in a 96-hour static test, and the 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 fish exposed to 0.0 or 0.5 mg/L UIA, but 93-100% mortalities were observed within 24 hours among fish exposed to 2.0, 3.0, or 4.0 mg/L UIA. The calculated no effect level (NOEL; the maximum UIA concentration at which the UIA would have no long-term effects on growth or survival) was 0.131 mg/L UIA at 24 h. 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) Streptococcus agalactiae per fish. While the UIA concentration used was lower than the LC50, it was still considerably higher than the NOEL and would thus potentially promote stress responses, morbidity, and mortality. However, mortalities of UIA exposed and control fish were not significantly different 21 days post-challenge. Blood glucose levels were also 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.