Ammonia toxity to juvenile acanthobrama telavevinses (Cyprinidae), A critically endangered endemic fish in the coastal plain of Israel

We assessed the toxicity of ammonia to Acanthobrama telavivensis, a critically endangered endemic cyprinid that until the 1950s was very common in the coastal stream system, but is now restricted to a few unpolluted reaches. Ammonia toxicity was determined by a 96-h LC50 bioassay in a flow-through system with fish mortality as the end point. Acute toxicity of un-ionized ammonia for juvenile A. telavivensis is 1.00 mg 1^-1 NH₃-N (0.94-1.06, 95% confidence limits), which corresponds to 20.1 mg 1^-1 total ammonia nitrogen at pH 8.0, total hardness of 250 mg/1 (as CACO₃), and temperature of 24.2 °C. Acute-to-chronic ratio (ACR) values of 7.2, 10.9, and 16, suggested in the literature, yielded estimated safe ammonia concentrations for A. telavivensis of 0.14, 0.09, and 0.06 mg 1 ^-1 NH₃-N, respectively, using the accelerated life testing (ALT) procedure. Accordingly, the 0.01% acceptable risk concentrations for 60 and 90 days are 0.17 and 0.16 mg 1^-1 NH₃-N, respectively, agreeing with the safe ammonia concentration calculated by an ACR value of 7.2. No-observed-effect-concentration of <0.2 mg 1^-1 NH ₃-N may explain the absence of this cyprinid from the polluted sections of the Yarqon Stream, where the average un-ionized ammonia-nitrogen level typically exceeds 30 mg 1^-1 NH ₃-N. Adoption of a 0.01% acceptable risk concentration for 90 days, of 0.16 mg 1^-1 NH₃-N, will allow existence of this critically endangered endemic fish, at least in those streams where ammonia is the limiting pollutant.