The role of ovarian steroids in reproductive plasticity in Hoplias malabaricus (Teleostei: Characiformes: Erythrinidae) in tropical reservoirs with different degrees of pollution.

Chemicals in aquatic environments may lead to impairment of fish reproduction, but some species display plasticity levels to survive and reproduce in such localities. We investigated the reproductive cycle in a teleost species, Hoplias malabaricus, which inhabits a variety of environments with different degrees of pollution. Adult females were sampled at two locations in São Paulo State (Brazil), the reference Ponte Nova (PN) reservoir and the polluted Billings (BIL) reservoir. Metabolic and endocrine processes were analyzed throughout the annual cycle with special attention to ovarian histology, gonadosomatic index (GSI), fecundity, ovarian energetic substrates and plasma steroids analyses, in addition to physical and chemical analyses of the water. Pollutants were frequent in BIL but not in PN. The GSI, including the predominance of vitellogenic oocytes, was higher in spring and summer in both locations, but the oocyte recruitment dynamics was different. During winter, females from BIL presented vitellogenic oocytes and high levels of 11-ketotestosterone, which indicated precocity in the vitellogenic phase in relation to the females from PN. In animals from PN, high deposition of lipids occurred in the ovaries. However, plasma estradiol levels did not vary throughout the annual cycle. In animals from BIL, plasma estradiol levels peaked during the summer, but the ovarian lipid content remained unchanged throughout the year. The data suggest that the presence of pollutants cause various endocrine and metabolic responses and especially affects reproductive plasticity, which could explain why H. malabaricus survives under unfavorable environments.