Lethal Concentration of Ammonia and Tolerable Range of pH in zebrafish (Danio rerio)

Increasing in water ammonia is one of the major problems in aquaculture. Nitrogen-containing materials are producing in different ways, including oxidation of nitrogen-containing organic matters such as proteins, manure decomposition and ammonia excretion by fish. The increase in these compounds in water recirculation systems and aquaria has always been considered as a stress-causing factor. On the other hand, either increasing and/or decreasing in ::union::ized ammonia are affected by pH changes. In order to obtain the LC50 of ammonia, zebrafish were exposed to seven treatments including control, 0.069, 0.138, 0.276, 0.552, 1.105 and 2.210 mg/L of ::union::ized ammonia. Then, in order to obtain a tolerable pH range fish were exposed to either gradual increase or decrease of pH (0.1 units per minute) using HCl and NaOH 0.4 N. The amount of LC50 for different time periods was determined using the probit software. The amounts of LC50 for 24, 48, 72 and 96 hours were 0.766, 0.634, 0.532 and 0.471 mg/L, respectively. Maximum and minimum average of pH tolerance threshold was 11.64±0.04 and 2.60±0.09 respectively. The results showed that zebrafish is a sensitive species to ammonia poisoning, but it is resistant to pH changes.