| AMMONIA TOXICITY TO JUVENILE ACANTHOBRAMA TELAVIVENSIS (CYPRINIDAE), A CRITICALLY ENDANGERED ENDEMIC FISH IN THE COASTAL PLAIN OF ISRAEL |
ELDAD ELRON A1, MENACHEM GOREN A1, DANA MILSTEIN A1, AVITAL GASITH A1
A1 Department of Zoology and Institute for Nature Conservation Research, George S., Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, 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 l-1 NH3-N (0.94-1.06, 95% confidence limits), which corresponds to 20.1 mg l-1 total ammonia nitrogen at pH 8.0, total hardness of 250 mg/l (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 l-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 l-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 l-1 NH3-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 l-1 NH3-N. Adoption of a 0.01% acceptable risk concentration for 90 days, of 0.16 mg l-1 NH3-N, will allow existence of this critically endangered endemic fish, at least in those streams where ammonia is the limiting pollutant.
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