LERNER, D.T.*; DAVIS, L.K.; MCCORMICK, S.D.; HIRANO, T.; GRAU, E.G.; Univ. of Massachusetts, Amherst; Hawaii Institute of Marine Biology, Univ. of Hawaii, Kaneohe; USGS, Conte Anadromous Fish Research Center; Hawaii Institute of Marine Biology, Univ. of Hawaii, Kaneohe; Hawaii Institute of Marine Biology, Univ. of Hawaii, Kaneohe: Effects of 4-nonylphenol and 17β-estradiol on osmoregulatory homeostasis and endocrine responses of Mozambique tilapia, Oreochromis mossambicus
Mozambique tilapia, a euryhaline cichlid, has been widely used as a model for examining hormonal control of ion regulation in fish. Transfer from fresh water (FW) to seawater (SW) elicits temporary increases in plasma osmolality, ion concentrations, and gill Na+, K+-ATPase activity (NKA). There is evidence that growth hormone (GH) and insulin-like growth factor I (IGF-I) play a role in SW acclimation in this species. We examined the effects of nonylphenol (NP) (a xenoestrogen) and estradiol (E2) on the maintenance of osmoregulatory homeostasis and endocrine responses in FW- and SW-adapted tilapia. Male fish (mean weight; 100 g) were acclimated to either FW or 100% SW (35 ppt) for 2 weeks. They were injected ip. with either E2 (5 mg/kg), NP (150 mg/kg), or vehicle (vegetable oil). A second injection was given on day 3, and blood, gills and livers were sampled from all fish on day 6. Treatment with E2 increased plasma vitellogenin 10-fold, while NP-treated fish exhibited a 2-fold increase. Plasma prolactin, GH, IGF-I, chloride, and NKA were not affected at either salinity. E2 treatment reduced liver GH receptor (GHR) and IGF-I mRNA by approximately 50% in FW and SW. NP increased gill GHR 2.5-fold in FW only. Both E2 and NP increased gill IGF-I mRNA 100% over controls in FW. We conclude that while E2 and NP did not impair osmoregulatory ability in FW- or SW-acclimated tilapia, they did impact GHR and IGF-I mRNA, and therefore warrant future studies on the long term effects of estrogenic compounds on salinity tolerance, growth, and development.