Response of Sex Steroid Hormone Synthesis Substrates in Serum and Testes of Male Tilapia (Oreochromis niloticus) Exposed to Methomyl and Its Recovery Pattern

The response of synthetic substrates of sex steroid hormones—cholesterol (CHO), pregnenolone (PREG), and progesterone (PROG)—in the serum and testes of male tilapia (Oreochromis niloticus) to the environmental estrogen pesticide methomyl (0.2, 2, 20, and 200 μg·L−1) was evaluated using static-water contact toxicity tests. The results showed that low methomyl concentrations (0.2 and 2 μg·L−1) had no significant effects on the contents of CHO, PREG, and PROG in the serum and testes of male tilapia (p > 0.05). Consequently, the concentration of 2 μg·L−1 could be used as a preliminary reference threshold for the non-effective dose of methomyl in male tilapia. Exposure to high methomyl concentrations (20 and 200 μg·L−1) significantly inhibited the levels of CHO, PREG, and PROG in the serum and testes of male tilapia (p < 0.05) and showed a dose–response relationship. Sex steroid hormone synthesis substrate damage to male tilapia caused by less than 20 μg·L−1 methomyl was reversible, while the damage caused by equal to or greater than 200 μg·L−1 methomyl was irreversible when tilapia were transferred to methomyl-free water for 18 days. Thus, a concentration of 200 μg·L−1 could be used as a reference threshold for irreversible damage caused by methomyl in male tilapia.