Maturação da ostra do mangue (Crassostrea gasar) em laboratório sob diferentes condições de temperatura e salinidade

Abstract

Mollusks ranked third in global aquaculture production in 2016 and hold significant production potential in Brazil. The coastline of Maranhão features vast estuarine areas suitable for oyster farming; however, the industry faces obstacles such as a lack of seed stock—currently obtained solely from the wild—due to the absence of hatcheries producing seed for the mangrove oyster Crassostrea gasar in the North and Northeast regions. Gonadal maturation can be induced in the laboratory by manipulating water variables, such as salinity and temperature, which directly influence the reproduction of these organisms. This study aimed to evaluate the process of gonadal maturation under controlled laboratory temperatures and salinities. Two experiments were conducted to test four temperature conditions (Experiment 1: T1 constant 32°C; T2 constant 24°C; T3 varying from 32°C to 24°C; and T4 varying from 24°C to 32°C) and four salinity conditions (S1 constant 40; S2 constant 20; S3 varying from 40 to 20; and S4 varying from 20 to 40). The experiments took place in 12 L rectangular tanks (53 x 32.5 x 10 cm) set up within a recirculating system with constant water exchange, with 35 oysters stocked in each experimental unit. Feed was provided twice daily at a density of 10 x 10⁴ cells mL⁻¹. A significant prevalence of females over males was observed in both experiments, with hermaphroditism occurring in 0.5% of the broodstock only in the salinity experiment. Condition index (CI) results showed increased values ​​at temperatures between 24°C and 26°C and a salinity of 20. Gonadal stages of C. gasar broodstock indicated high gamete maturation (stage IIIA) at temperatures between 24°C and 26°C and a salinity of 20. Increases in temperature and salinity favored gamete release (stages IIIB and IIID). The gonadal occupancy index (GOI) showed increased gamete occupancy within the gonad at temperatures between 24°C and 28°C; while salinity led to significant value fluctuations, the results were similar across all treatments, with an average of 45%. Our results revealed a maturation pattern for the mangrove oyster C. gasar, which is favored by temperatures between 24°C and 26°C and salinities between 20 and 25. Thus, lower salinities and temperatures—or maintaining these lower levels—promote increases in CI and GOI, whereas increases in these variables result in a higher proportion of developing oocytes and gamete release.