Estudo da gametogênese e maturação gonadal do pacamã Lophiosilurus alexandri em condições de cultivo

Abstract

Few native fish species with potential for fish farming have fully developed and consolidated production technology for the different stages of cultivation. The aim of this study was to analyze the gametogenesis and gonadal maturation of the pacamã, Lophiosilurus alexandri under culture conditions, relating the reproductive parameters with the physiological conditions of the fish. For this, adult specimens (first filial generation of wild breeding) previously kept in a tank with 10,000 L of water at 23°C in the Aquaculture Laboratory of the UFMG (LAQUA) were transferred to circular tank with 3,000 L of artificially heated water at 27°C. Fish sampling was performed in four periods: the first, before water heating (T1 group, water at 23ºC) and the subsequent three periods at 20 and 40 (T2 group) and 70 (T3 group) days after heating water at 27°C. Two couples were placed in a sand-bottom tank with water heated at 27ºC in order to verify the nest formation and spawning occurrence. The physico-chemical parameters of the water were monitored daily to ensure optimum conditions of cultivation. Biometric data, physiological indicators and blood parameters of the fish were obtained from each specimen. Samples of gonads and liver were collected for histological processing and ELISA. The frequency of maturing females was higher in T3, where the best reproductive parameters were found: higher IGS, vitellogenic follicle diameter and follicular cell height, which were associated with the higher serum concentrations of 17β-estradiol and hepatic levels of vitellogenin. On the other hand, there was a high frequency of females with regressing ovaries in T1 and a high index of follicular atresia in ovaries. The absolute fecundity in T3 varied from 5,449.364 to 12,581.74 oocytes per female. Serum levels of 17α-hydroxyprogesterone varied discretely between collection times, rising from T2 to T3, where females reached final oocyte maturation. However, no spawning was found in the bottom of the tank, even when couples were placed in sand-bottom tank. In males, serum levels of 11- ketotestosterone increased considerably after water heating (T2 and T3), but reproductive parameters were similar in all three sampling groups. The presence of intersex males (11%) and levels of vitelogenin and proteins of the zona radiata similar to that of the females, without an apparent disorganization of the testicular structure and spermatogenesis, is a concern regarding the occurrence of endocrine dysregulation in captive conditions. Significant differences in the hematological and biochemical variables were observed in T2 and T3, with increased blood glucose and number of iv erythrocytes in both male and female fish. Although seric concentrations of cortisol did not differ amongst collection times in males, significant differences were observed in females between times T2 and T3. Together, the results indicate that the increase in water temperature stimulates the gametogenesis and gonadal maturation of L. alexandri under culture conditions, with females being more sensitive than males to changes of the temperature. Maintenance of fish at low water temperatures (23ºC) induces follicular atresia in ovaries, which may reduce the reproductive potential of the species in captivity. The blood parameters presented physiological variations, which can be used as health indicators for L. alexandri kept in captivity.