The Acute Toxicity of Fenitrothion to Killifish (Oryzias latipes) at Twelve Different Stages of Its Life History

Abstract

The acute toxicity test of fenitrothion was conducted for 12 different stages of killifish (Oryzias latipes). The most sensitive stage was postlarva II (28 days after hatching) with 96 hr LC50 of 2.36 and 0.0049 ppm for fenitrothion and DDT, respectively, whereas the least was early stage of development (embryo) and the value for both compounds was more than 10 ppm. The embryo exposed to fenitrothion at and above 5 ppm for the whole period of embryo (8 days) or a shorter period of exposure (3 days) showed some adverse effects on development of circulatory organs, hatchability and survival of the fry. On the contrary, DDT affects not the development of embryo, but mortality of the fry resulting from exposure to embryo even at the level of 0.05 ppm. No significant difference in toxicity between male and female and also among various stages of maturity was observed. Throughout the tests using life history, the minimum LC0 value at 96 hr was found to be 1.0 ppm and less than 0.001 ppm for fenitrothion and DDT, respectively. These results with fenitrothion were compared with inhibition of cholinesterase activity (I50) by its oxon analog. © 1984, Pesticide Science Society of Japan. All rights reserved.