Extenders and semen:extender ratio in the cryopreservation of sperm of fat snook Centropomus parallelus

Abstract

Aiming to develop semen cryopreservation methods of the fat snook, Centropomus parallelus, studies were carried out in the Instituto de Pesca-SP, to optimize the sperm motility and motility time and semen fertilization capacity. Fifty reproducers, originated from artificial reproduction, were brought up in cages that were set in oceanic environment. The semen, diluted in three Ringer’s solutions (pH 6.1, 7.8 and 8.2) in the proportions of 1:1, 1:2, 1:3, 1:4 and 1:5, was frozen by nitrogen vapor and later on, transferred to liquid nitrogen. The cooling rate, the dimethyl sulfoxide (DMSO) cryoprotector concentration and the equilibration time were 90°C min^-1, 10% and 60 seconds, respectively. The fertilization capacity was determined by calculating volumes of semen necessary to obtain the sperm:egg proportion of 4x10⁴, 1x10⁵, 1.6x10⁵ and 2.2x10⁵. Regarding the spawning eggs, the females received human chorionic gonadotropin (hCG) and 1 IU/g body weight. Regarding fresh semen, the motility was 100%, as the motility time was 464.6 ± 47.56 seconds. For cryopreserved semen, the best results for a 70.0 ± 3.94% motility and 610.8 ± 9.60 seconds motility time, using the diluent with an 8.2 pH. No significant differences (p<0.01) were observed regarding the different semen:diluent proportions. Finally, equal (p<0.01) fertilization rates (99.0 ± 0.66%) were obtained from 1.6x10⁵ sperm:egg concentration, indicating that cryopreservation sets itself as an important resource for semen stocking and the fat snook reproduction control.