Acute Toxicity of the Pesticides MEP (organophosphate) and NAC (carbamate) to Larvae of Red Sea Bream, Pagrus major and Japanese Flounder, Paralichthys olivaceus

Abstract

Acute toxicity of the organophosphate “MEP” [O, O-dimethyl O- (3-methyl-4-nitrophenyl) phosphorothioate] and the carbamate “NAC” [1-naphtyl-N-methylcarbamate] to larvae of red sea bream, Pagrus major and Japanese flounder, Paralichthys olivaceus was determined by static water bioassay. Red sea bream larvae (5-47 days after hatch) were arbitrarily divided into 5 developmental stages. Japanese flounder larvae (3-60 days after hatch) were divided into 8 developmental stages. Susceptibility of each stage to the above pesticides was investigated. In all stages of red sea bream larvae, the values of 24hr LC₅₀ were 1.2-1.7 ppm for MEP and 0.9-3.2 ppm for NAC. In all stages Japanese flounder larvae, the values of 24hr LC₅₀ were 0.8-2.8 ppm for MEP and 0.9-3.2 ppm for NAC. In both species, susceptibility to the pesticides was unrelated to the developmental stage. Apparent neurotoxicity symptoms were induced in larvae exposed to MEP and NAC, such as loss of equilibrium, decrease in spontaneouse motor activity, change in body color to dark, and wild excitement.