Abstract: Miamiensis avidus is a common marine pathogentic ciliate which can multiply quickly in eutrophic waters, causing fish disease and great loss to fishery resources and aquaculture. There are no drugs to prevent fish from being infected until now. In recent years, Sodium chloride, Mercury chloride, Trichlorfon, Cupric sulfate have been commonly used in aquaculture, but there was no report on the toxicity of four drugs to animals low on the aquatic food chain. In this study, the toxicity of four drugs to M. avidus was investigated. M. avidus was cultured to a density of 2 500 ind/mL, at 25℃ and a light intensity of 1 000 lx. Based on the result of pre-test , the effect of four drugs（sodium chloride: 0, 200, 400, 600, 800, 1 000 mg/L; Mercury chloride: changes in population density at 0, 0.002, 0.004, 0.006, 0.008, 0.010 mg/L; Trichlorfon: 0, 100, 200, 300, 400, 500 mg/L; Cupric sulfate: 0, 0.010, 0.015, 0.020, 0.025, 0.030 mg/L）was studied. The tests showed that four drugs all inhibited the population growth of M. avidus. Respectively, the sodium chloride 800 mg/L, Trichlorfon 500 mg/L, Cupric sulfate 0.03 mg/L, Mercury chloride 0.01 mg/L, the inhibition of M. avidus population growth is the most obvious.

Key words: Miamiensis avidus, sodium chloride, trichlorfon, cupric sulfate, mercury chloride, population growth