Induced spawning of snook Centropomus parallelus Poey, 1860

Abstract

The snook Centropomus parallelus, an important fish of the Brazilian coast, was induced to spawn with the aid of hCG (human chorionic gonadotropin) in November and December/1996 and January/1997, at the Laboratory of Mariculture of Cananéia - SP, Brazil (25º 01 S; 47º 57 W). The females (n = 26) received one dose of hormone containing 1, 2 or 5 IU of hCG per gram of body weight. These females were chosen observing initial mean oocyte diameter, the distribution of the different diameter values, and location of germinal vesicle. Four females were considered as control and received one unique injection of 1 ml of 0.9% saline solution. The initial mean oocyte diameter of the selected females was around 400 µm and the distribution of oocyte diameters was unimodal with the mode in 435.6 µm. Approximately 35 hours after the injection of the hormone, females initiated the release of eggs. Then, the eggs were extruded and dry fertilization performed with sperm. At this time, the mean egg diameter was above 600 µm, one oil droplet was present and the germinal vesicles were breakdown. Many larvae were obtained with either one of the above different hormonal doses, 18 hours after fertilization. The ratio of fertilization ranged between 70 and 90%. During the incubations, the sea water salinity was maintained between 29 and 35%, and the temperature was 25 ± 1ºC. Males did not receive hormone. They were selected taking into account the amount and viscosity of milt released and with spermatozoa motility around 90%. The body weight of the fishes varied from 210 g to 1,740 g and the length, from 25.7 to 56.0 centimeters.