Analysis of hormone profile in Astyanax bimaculatus females with positive response to reproductive stress protocol in fish farm

PARREIRA, W. S. P.; MOREIRA, R. G.; HONJI, R. M.

Olhão

Simposio; 10th International Symposium on Reproductive Physiology of Fish; 2014

Introduction Stress can be defined as a condition in which the dynamic equilibrium of the body is disturbed. In this field, several studies have demonstrated the action of some corticosteroid hormones modulate stress situations, such as reproduction. However, the role of corticosteroids in fish reproduction can be either positive or deleterious, depending on many variables. Interestingly, in the Astyanax genus, the same stress stimulus can successfully induce the reproduction in A. bimaculatus, but not in other species of the genus. Therefore, the aim of this study was to analyze the cortisol and progestogens levels of Astyanax bimaculatus, a species that successfully reproduce using stress as a stimulus. Methods For this study, a reproductive protocol using stress conditions was used to stimulate spawn. The stress protocol is used regularly and successfully at CESP (Companhia Energética do Estado de São Paulo) for restocking program purposes. This protocol consists of keeping A. bimaculatus males and females together in a tank in a very high density (1.5 fish/m3) and an intense water flow (10L.m-1). We chose 3 experimental groups for testing: Stress (just described); human chorionic gonadotropin (hCG; 5UI.g-1); and Serum (animals injected with NaCl 0.37% in the same hCG volume). To assess the hormonal status of the animals, 5 individuals were collected at 0, 8, 12 and 24 hours after the beginning of the treatment. Plasma samples were collected from the caudal vein to measure 17-hydroxiprogesterone (17-OHP) and cortisol (CORT) by ELISA immunoassay; and ovaries were fixed in Bouin solution to analyze the maturation stage of the oocytes, by histological analysis. Results and Discussion The experiment lasted 24 hours when females from the hCG and Stress groups successfully spawned. At 12 hours after the beginning of the experiment, there was a sudden increase in plasma levels of CORT in females from the Stress group, but not in the hCG and Serum groups. 17-OHP did not change during the experiment and also did not differ among groups. Considering that 17-OHP is a precursor of the maturation-induced steroid (MIS, 17-20!- dihydroxiprogesterone), we expected to observe a peak of this progestogen closer to the time of ovulation. In the ovaries, the presence of mature oocytes was observed in the first half of the experiment in all groups, and, at 24 hours, a great amount of postovulatory follicles, but there were still cortical alveoli oocytes in the ovaries of females in hCG and Stress groups. Conclusion We suggest a possible role for CORT in stimulating the reproductive activity, with a direct influence on ovulation and/or spawning of A. bimaculatus, and with a positive action as an inducing agent in the spawning of this species.