Ciclo gametogênico de Poecilia reticulata (Cyprinodontiformes : Poeciliidae) analisado em condições naturais antrópicas em um córrego urbano de Cuiabá, MT, Brasil

Abstract

The description of the reproductive cycle involves, among others, the morphological characterization of the gonads with the determination of the periods in which gametic proliferation and differentiation occur. In this context, the histological evaluation of the gonads is important to determine the reproductive period and observe the gametogenic cycles. This study aimed to describe the gametic cycle of a fish species (Poecilia reticulata), living in an anthropized urban environment. Monthly collections of specimens of the species Poecilia reticulata (Cyprinodontiformes, Poeciliidae) were carried out in a small urban stream on the campus of the Federal University of Mato Grosso (UFMT), municipality of Cuiabá – MT. The samples were collected from June 2019 to May 2020, with intervals of 30 days between each collection. We measured the total length and total weight of each specimen and only for females we analyzed the gonadosomatic ratio. Sexually mature adult males and females were histologically analyzed, as well as some juveniles that, before histological processing, it was not possible to determine the sex. The number of oocytes and embryos was quantified in a magnifying glass and prepared for histology. The analyzes showed that the number of individuals collected in the stream varied throughout the year, and this variation is likely related to the low rainfall during the dry season, a period in which the stream even dried up, in September 2019. When compared to males, we noticed that females have significantly higher values for body weight and length, probably due to the presence of a greater amount of embryos in the abdominal cavity. The increase in the size and body weight of females is possibly related to an increase in the volume of rain at the site. The gonads showed all cell types of spermatogenesis and oogenesis, and the presence of embryos during all months analyzed. Thus, the gametogenic cycle was classified as continuous for both sexes. From a gametic point of view, the results demonstrate that P. reticulata has physiological conditions to reproduce continuously. Furthermore, the data suggest that populations of P. reticulata that inhabit urban streams can adapt efficiently to adverse conditions, including the gametogenic aspect.