Journal of Aquatic Ecology

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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.

Keywords: Ammonia, Danio rerio, LC50, Zebra fish

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