Alternation of Pituitary-Testicular Axis in the NileTilapia (Oreochromis niloticus) Exposed to Dimethoate: An Immunohistochemical and Hormonal Study

The adverse effects of organophosphate dimethoate on testis morphology, luteinizing hormone (LH) cells structure and hormonal assay of the Nile tilapia (Oreochromis niloticus) were examined. Adult male tilapia, average body weight 150.0±23.3 g, were exposed to environmentally relevant (0.03 mg/L-1) and sublethal (5.00 mg/L-1) doses of dimethoate for 15 and 30 days. Fish exposed to 0.03 mg/L-1 dimethoate exhibited significant decrease in the serum LH. While, 5.00 mg/L-1 dimethoate revealed significant increase in serum LH. Follicle stimulating hormone (FSH) displayed significant increase in 5.00 mg/L-1group exposed for 15 days. However, a significant reduction was observed in 0.03 mg/L-1group exposed for 30 days. Histological structure of the testes of the control tilapia showed numerous spermatogenic cysts; lumina filled with spermatozoa and little interstitial tissue. Fish exposed to dimethoate for 15 days showed scarcely spermatozoa, narrow seminiferous tubules and increase in the interstitial connective tissue. After 30 days, 5.00 mg/L-1 exposed fish showed progressive reduction of spermatozoa, empty tubules and a degenerative cell debris in the lumen of the seminiferous tubules. Immunohistochemically, the LH cells were localised in proximal parse distalis of the tilapia adenohypophysis. LH cells were isolated, clustered or formed cord of cells surrounding the neurohypophyseal branches. In dimethoate exposed fish, LH cells displayed a reduction in size and mass distribution in the adenohypophysis. The cytoplasm of the LH cells were vacuolated and showing the sings of degeneration. The changes appeared in testicular structures and LH cells of the O. niloticus were in a dose and time-dependent manner. Based on these observations, sublethal or environmentally relevant concentrations of dimethoate exhibited an endocrine disruptive action at pituitary-testicular axis of Nile tilapia that might lower its reproductive potential.