Subchronic effects of cadmium on the gonads, expressions of steroid hormones and sex-related genes in tilapia Oreochromis niloticus

Cadmium (Cd) is one of the most toxic heavy metals in aquatic ecosystem which affects fish health and aquaculture. In the present study, we examined the bioaccumulation of Cd in the gonads of tilapia via dissolved and dietary routes. We evaluated the subchronic effects of Cd on the histology of gonads, steroid hormone levels and sex-related gene expressions in tilapia. In addition, we also studied maternal transfer of Cd. Our results indicated that Cd was accumulated significantly in both ovary and testis from both exposure routes. Histopathological analysis showed that Cd induced ovary and testis injuries. Estradiol levels were significantly increased in dissolved Cd exposed female fish. In addition, the Cd exposure displayed different effects on gene expressions in gonads. In females, the estrogen receptor (ER alpha) was stimulated in dissolved Cd-exposed fish at 70.32 and 143.78 mu g/L for 30 days and in fish at 143.78 mu g/L for 60 days. Vitellogenin expression was significantly down-regulated in the ovary of dissolved Cd-exposed fish. In testis, GR expression was elevated after 60 days of dissolved Cd and dietary exposure. Furthermore, Cd level was significantly higher in the eggs than that in the fry. Our results demonstrated that both dissolved and dietary Cd exposures affected gonad development by altering steroid hormone levels and sex-related gene expressions in tilapia.