Effects of malathion on steroidogenesis and sex reversal in Monopterus albus

Abstract

Monopterus albus in their female phase were exposed to Malathion at a concentration of either 9 ppm for four weeks to study the acute effects on steroidogenesis or 3 ppm for seven months to study the chronic effects on the process of sex reversal. Gonadal tissue obtained from Malathion-exposed fish showed a lower rate of in-vitro testosterone and estradiol production than controls. Addition of homologous pituitary extract or human chorionic gonadotrophin to the medium could partly overcome this inhibitory effect of Malathion on steroid production. Aromatase activity (assessed indirectly by measuring the conversion of exogenous testosterone to estradiol) was found to be significantly lower in the ovaries of Malathion-exposed fish. However, since the production of testosterone by the ovarian follicles of exposed fish was lower than that of controls, Malathion may also be interfering with biosynthetic steps prior to testosterone formation. Long-term treatment of females with Malathion resulted in massive morphological damage to the gonads. The gonads of these fish were filled with degenerated testicular lobules and atretic oocytes. Moreover, the Malathion-exposed group had a lower number of functional intersexes and males after seven months of exposure than controls.