Waves of follicle development, growth and degeneration in adult ovary of zebrafish (Danio rerio) on chronic exposure to environmental estrogens in laboratory.

Patterns of quantitative production of follicles, their growth, and degeneration in the adult ovary of zebrafish (Danio rerio) in response to long-term (80 days) exposure to environmental estrogens (EE) in the laboratory, were studied. Experimentally naive female D. rerio procured from fish farm were acclimated to the laboratory (natural temperature, 26 ± 1° C, photoperiod, 11.30 L:12.30 D) for two weeks and divided into 10 groups. Each group (n = 20) was housed in a separate glass aquarium containing 10 L of conditioned water (physico-chemical parameters maintained within the permissible range prescribed for zebrafish) along with either 5 ng or 10 ng/L of 17α-ethynylestradiol (EE) or diethylstilbestrol (DES) or bisphenol A (BPA) or estradiol 17-β (positive control) or water with no chemical (negative control). All experimental fish were fed twice daily on commercial pellets (ad libitum) supplemented with Artemia nauplius, the exposure was semi-static and chemical residues in media samples were determined by ultra-performance liquid chromatography (UPLC). Exposure of fish to estrogens increased (p < 0.05) (i) body mass and gonadosomatic indices (GSI) in E, EE and DES groups (ii) previtellogenic and vitellogenic follicles in E and EE groups (iii) atretic follicles (AF) in DES and BPA groups compared to controls and (iv) decrease in total oocyte volumes (V = 4/3. π. r) compared to those of E group. These results suggest that the chronic exposure of fish to EE (at environmentally relevant concentrations) has a profound influence on ovarian follicular dynamics and the effects of individual EE are discrete on the ovary.