Caracterização dos ovarios e do desenvolvimento ovocitario, e da recuperação ovariana pos-parto do platy (Xiphophorus maculatus) (Teleostei, Poeciliidae) em condições laboratoriais controladas e sob ação do hormonio de crescimento

AUTOR(ES)
DATA DE PUBLICAÇÃO

2004

RESUMO

The platy Xiphophorus maculatus (Poeciliidae), is an ornamental freshwater fish, ovoviviparous and able to produce offspring throughout the year, when maintained at the ideal temperature and photoperiod. This fish is considered a promising species for wide scale production and easily adaptable to laboratory conditions. It presents internal fertilization, sperm storage in the ovary permitting sucessive fertilizations, intra-follicular gestation, and sexual dimorphism. Some studies have been made using the platy as an experimental mode!. However, considering the peculiarities of the reproductive biology of X. maculatus and its potential for the study of gametogenesis, little is known about germ cell morphology. The histological study leads to basic knowledge of their reproductive biology with practical application for the understanding of fertilization, initial embryo development and larvae growth. The success of fishculture basically depends on the knowledge of fish biology, and particularly of the reproductive process. The present work includes oocyte development, the characterization of the ovary and post-partum ovarian recrudescence in the platy (Xiphophorus maculatus), analyzing the structural events observed in controlled conditions. Research has shown that growth hormone is also involved in gonadal maturation, gametogenesis and ovulation, being an important modulator of female reproduction. Therefore, the effect of growth hormone (GH) in ovarian recrudescence has been analyzed in post-partum females. The present study also determines the size of females at first sexual maturation, that is essential for understanding of reproductive biology in fishes. In this study, juveniles and adult females of X. maculatus were kept in aquariums. The ovaries were removed and prepared for study of oogenesis with the light and electron microscopes. According to established post-partum periods, ovaries of the control and growth hormone (GH) treated groups were collected and prepared for the study of ovarian post-partum recrudescence with light microscopy. Gonads of the control and treated groups were also prepared for the deteccion of growth hormone by immunohistochemistry. Moreover, the values of the gonadossomatic (IGS) and hepatossomatic (IHS) index were calculated, as well as the condition factors (K1 and K2), in the different post-partum periods for the two study groups. To determine the size of the first sexual maturation, juveniles and small pieces of their ovaries were collected. Standard body length, body weight and the age of each fish were recorded for the calculation of the LSO. The ovarian structural organization showed that the female genital tract possesses structures for spermatozoa storage. Oogenesis in X. maculatus, an ovoviviparous species, is similar to that described for most of the freshwater fish. In the study of the size of first sexual maturation (L50), the platy were considered mature with 2,O3cm of standard body length, and the estimated size when ali the population is considered mature (L1oo) was 2,Scm. With this size, gravid female were observed. No immunostaining was observed for the growth hormone in the ovaries, neither in the control group nor in the treated group. This result probably is related to the low concentration of the growth hormone in the ovary, or the short half-life of this hormone, or even the dosage used in the treatment which did not allow immunostaining. During gestation new oocytes initiate vitellogenesis. However, the oocytes which develop during the gestation enter atresia, and therefore will not be fertilized. In females treated with growth hormone, atresia continues to occur 72, 84 and 96 hours post-partum, indicating that the eggs that had initiated postpartum maturation also entered atresia. This event may have been due to the hormonal treatment. As estresse is an important factor causing follicular atresia in fish, the manipulation to anesthetize and administer the hormone probably stimulated the atretic process

ASSUNTO(S)

ultraestrutura (biologia) ovario reprodução teleosteos

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