Abstract
The toxicity of ammonia and its effects on growth inhibition for the marine ciliate, Euplotes vannus, were measured in a conventional open system. Linear regression analysis showed that: the 2 hour median lethal concentration (LC50) was 7870.46 mg total ammonia-N l−1 (P<0.05; pH 8.2; salinity 28 ppt; temperature, 25 °C ); the threshold concentrations for growth inhibition was 100 mg total ammonia-N l−1 (P<0.05; pH 8.2; salinity 28 ppt; temperature, 25 °C); and the toxicity curve equation for 24 hours was y=113.48e−0.0005.4x (P<0.05, R=0.94; y = culture time; x = LC50), from which it is possible to predict LC50 values of a wide range of ammonia-N concentrations for almost any exposure time. The results demonstrate that the tolerance to ammonia in E. vannus is considerably higher than that of the larvae or juveniles of some metozoa, e.g. cultured prawns and oysters. In addition, the results also determine that ciliates, as bacterial predators, are likely to play a positive role in maintaining and improving water quality in aquatic environments with high-levels ammonium, such as intensive aquaculture ecosystems.
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