Alterations in the Development and Gonadal Structure of Nile Tilapia (Oreochromis niloticus) Exposed to Natural and Synthetic Estrogens

This study aimed to investigate the effects of endocrine disruptors 17 beta-estradiol (E2) and 17 alpha-ethinylestradiol (EE2) on Nile tilapia (Oreochromis niloticus) development, focusing on gonadal histological factors. Concentrations of estrogens E2 and EE2 ranging from 250 to 1000 ng center dot L-1 can produce intersex individuals, significantly decreasing the condition factor as the concentrations increased. These concentrations could also induce the development of morphological anomalies. Increasing the concentration of estrogens by one order of magnitude (mu g center dot L-1) was lethal for Nile tilapia larvae, with no effect on the incubation time and percentage of larvae hatching. Additionally, morphological anomalies and developmental problems were observed. Estrogens applied at a concentration of 160 mu g center dot L-1 for 28 days caused the birth of a small number of intersex individuals in Nile tilapia, but generated almost entirely female populations in hormonal treatments. Furthermore, the gonads of fish exposed to the estrogens were smaller and less developed, without any significant difference between E2 and EE2. Variation in the exposure time (one to 4 weeks) of Nile tilapia to estrogens (160 mu g center dot L-1) resulted in the appearance of intersex individuals and the development of morphological anomalies, regardless of the exposure time.