Inhibition of thyroidal status related to depression of testicular development in Sebastiscus marmoratus exposed to tributyltin

Organotin compounds, such as tributyltin (TBT), which have been used as antifouling biocides, are still of concern with regard to their effects on marine organisms, and especially their reproductive systems. We investigated the toxicity of TBT at environmentally relevant concentrations (1, 10, and 100 ng/L) on testicular development in a marine fish, Sebastiscus marmoratus. After exposure for 50 days, the gonadosomatic index had decreased in a dose-dependent manner, and there was a reduced number of mature sperm and an abundance of the late stages of spermatocysts in the testes of S. marmoratus. Exposure has also caused serious histological damage to the testes including interstitial fibrosis and pyknotic nuclei. Analysis of the thyroid status revealed severe damage to the thyroid gland, decreased triiodothyronine and thyroxine in the serum and low expression of thyroid hormone receptor alpha in the testes at this time. Pearson correlation analysis indicated that the levels of thyroxine in the serum were significantly correlated with the gonadosomatic index. These results suggest that inhibition of thyroidal status induced by TBT might be one of the mechanisms affecting testicular development.