Lethal and sub-lethal effects of DDT, carbofuran, trifenmorph and niclosamide on oreochromis niger gunther (1898)
Oreochromis niger fry were exposed to various concentrations of DOT, Carbofuran, Trifenmorph and Niclosamide to determine the toxicity of these chemicals to the fish. The concentration lethal to 50% of the fish population in a given time range 24 hrs - 96 hrs, for each of the chemicals, was determined. The growth and swimming patterns of these fish in sub - lethal concentrations of the biocides were also studied. DOT was found tobe the most poisonous to fish with a 24 hr LC 50 of 0.042mg/litre. Carbofuran was the least toxic with an LC 50 of 0.225 mg/litre. The toxicity of all the four chemicals increased with concentration and time. The swimming. activity of the fish decreased with time in all the experiments except in Niclosamide. There was a negative linear relationship between fish activity and time. The fish increased weight very slowly from the first to the fifth week. Growth or increase in fish weight had a positive linear relationship with time in all the experiments. Increase in weight was however slower in the treatments than in the control except in sub - lethal levels of Carbofuran. The experiment shows that fish cannot be grown in water containing sub - lethal amounts of DOT, Trifenmorph and Niclosamide as they are highly toxic. The fish safe levels would be too low for the control of snails.