Effect of low-dose malathion on the gonadal development of adult rare minnow Gobiocypris rarus

•Adult rare minnow were exposed to 2 and 20 μg/L malathion for 21 days.•Malathion increased rare minnow testicular weight and promoted spermatogenesis.•Sex hormone and steroidogenic gene mRNA levels were altered in both sexes.•Low dose malathion could pose a potential threat to rare minnow gonadal development.

Malathion is an organophosphorus pesticide that extensively used in agriculture and veterinary practices. To investigate the effects of low dose malathion on rare minnow Gobiocypris rarus gonadal development, we exposed adult rare minnow to environmentally relevant concentration malathion (2 and 20 μg/L) for 21 days. Gonadal histology, sex hormone levels and mRNA expressions of steroidogenic genes were investigated. Malathion at both 2 and 20 μg/L significantly up-regulated rare minnow testicular weight and promoted the progression of spermatogenesis. Neither ovarian weight nor process of ovary development was markedly changed. In testis, 2 μg/L malathion significantly down-regulated testosterone and 11-ketotestosterone levels, and up-regulated mRNA expression of steroidogenic genes. In ovaries, 2 and 20 μg/L malathion significantly inhibited estradiol17β levels and induced testosterone levels, both in concentration dependent manners; mRNA expressions of almost all the detected ovarian steroidogenic genes were up-regulated. The present result suggested that malathion even at low dose could pose a potential threat to adult rare minnow gonadal development.