Caracterização microscópica do desenvolvimento de gônadas de tilápia do nilo (Oreochromis niloticus)

Abstract

Aquaculture is the fastest growing sector of agriculture worldwide. The Nile tilapia (Oreochromis niloticus) shows great aptitude for farming in aquacultural systems, and monosex farming yields better outputs due to the lack of reproduction and higher growth rates of males achieved mainly through masculinizing hormones. Assessing the efficiency of sex reversal procedures is very important for decision making during the process itself and for control of early fattening phases. This study aims to visually characterize developing and developed gonadal tissues of the animals after a period of ingestion of the synthetic androgynous hormone 17α methyltestosterone and to produce photographic documentation of sexual differentiation. The essay was conducted at the Fish Seed Production Facility of Consolata Agro-industrial Cooperative located in Nova Aurora, Paraná State, Brazil. After the initial embryonary development, tilapia larvae were fed a diet containing 17α-methyltestosterone in three hapa nets with a volume of one thousand liters (1000 L) each. The analyses were carried out at the Biochemistry and Genetics laboratory of the Federal University of Fronteira Sul (UFFS), on the Laranjeiras do Sul campus. The system was installed in an aquaculture greenhouse with constant aeration provided by paddle aerators. The type of fish feed used was powder, and the hormone 17α – methiltestosterone was added at the ratio of 60mg/kg of feed. The animals were fed for 55 days and after harvest they were anesthetized with 1% benzocaine and later stored in a 10% formalin solution. Preparations for direct analysis were made with acetocarmine dye, paraffin embedding for histological processing and hematoxiciline and eosine staining. Analyses were carried out with light microscope. It was possible to visualize characteristic and determinant structures of both sexes, such as oocytes (female sex characterization) and seminiferous tubules (male sex characterization), but the gonadal tissues did not present uniformity in their degree of maturation, being necessary the complete gonad analysis in order to identify regions with gonadal tissue characteristic of the sex.