FISHERIES RESEARCH INSTITUTE,MOA,TAIWAN

The aim of this study was to investigate the median lethal concentration (LC₅₀)of six chemicals on swamp eel (Anguilla marmorata) elver under two controlled temperatures, 20 ℃ and 30 ℃. Commonly used concentrations of agents were also examined for swamp eel. Under 20 ℃, the 96 hour LC₅₀ values of copper sulfate, potassium permanganate, formalin, Masoten, iodine preparation and Benzalkonium chloride (BKC) were 3.90, 1.75, 146.44, 5.46, 0.80, and 7.02 ppm, respectively. When temperature was 30oC, their LC₅₀ values were 3.06, 1.65, 131.46, 1.41, 0.69, and 6.91 ppm, respectively. These indicated that the agents were more toxic to the fish at 30 ℃ than at 20 ℃. The relative toxicity of iodine preparation was stronger than the other agents. The relative toxicity of agents was in the following order: potassium permanganate, Masoten, copper sulfate, BKC, and formalin at 20 ℃ and Masoten, potassium permanganate, copper sulfate, BKC, and formalin at 30 ℃. The results also showed that the commonly used concentration of 50-200 ppm iodine preparation for 10-15 min and 3-5 ppm potassium permanganate for long-term exposure were not suitable to swamp eel. Moreover, the exposure duration of 8, 100 and 500 ppm copper sulfate for 30, 20 and 1 min, 100 ppm Masoten for 60 min, 20 ppm potassium permanganate for 20 min, 200, 250 and 400 ppm formalin for 60, 30, and 15 min, respectively were suitable.