Gonadal and plasma testosterone level changes in male Nile Tilapia [Oreochromis niloticus (L.)] as induced by exposure to carbaryl, chlorpyrifos, and imidacloprid insecticides

The effects of low concentrations of carbaryl, chlorpyrifos, and imidacloprid insecticides on the reproductive system of male Nile tilapia, Oreochromis nilotics Linnaeus were determined. Five concentrations of each insecticide for both the juvenile and sexually mature fish set-ups were based from the reported 48-hr LC50 values. Only carbaryl at 3.52 x 10 sup-4 mg/L and 3.52 x 10 sup-1 mg/L treatment dose had significant difference on the relative testicular weight of juvenile O. niloticus (KW=12.041, P less than or equal to 0.05). There were no significant differences on the relative testicular weight of sexually mature male Nile tilapia. Fish at juvenile stage are more sensitive to carbaryl than at adult stage. The lowest concentrations to induce histological change were 3.52 x 10 sup-6 mg/L for carbaryl, 3.0 x 10 sup-7 mg/L for chlorpyrifos, and 1.336 x 10-4 mg/L for imidacloprid. At those levels of treatments, hemorrhagic necrosis was observed in the peripheral and interlobular interstitium of the seminiferous lobules in the testes of fish exposed to carbaryl and chlorpyrifos, while presence of adipose tissues were observed in the testes of fishes exposed to imidacloprid. Pyknosis and vacuolation occurred in the lobules of treated testes. As the treatment doses of the three test compounds increased, disorganization of testes structure also appeared to become severe. Extensive disintegration of interstitium and disorganization of lobules and cysts occurred at 0.1336 mg/L level of treatment of imidacloprid. Hemorrhagic necrosis was observed not only in lobules but at the spermatic duct as well. The observed degeneration of lobules correlated with the significant decrease in plasma testosterone levels at 0.1336 mg/L and 1.336 x 10 sup-2 mg/L (KW= 14.076, P less than or equal 0.05).