Cryopreservation of Prochilodus brevis semen: freezing media and thawing rates

Abstract

Prochilodus brevis is a migratory fish, an important component of its river ecosystem and an appreciated animal in northeastern cuisine. However, human activities have threatened its survival. Thus, researchers have become interested in developing genetic material storage protocols, such as seminal cryopreservation. Therefore, determination of the appropriate freezing media and thawing rate is a fundamental step toward the use of this biotechnology in the production of common curimatã and for reducing risks to the species’ survival. As such, the aim of the current study was to evaluate the effect of different freezing media and thawing rates on the quality of cryopreserved semen from P. brevis. For this study, males received a single dose of pituitary extract of carp 18 hours before semen collection. The semen samples were diluted in 5% glucose + 10% methyl glycol (MG), 5% glucose + 10% dimethyl sulfoxide (DMSO), 0.9% NaCl + 10% methyl glycol, and 0.9% NaCl + 10% dimethyl sulfoxide, loaded into 0.25-mL straws and frozen in liquid nitrogen vapor. The semen from each treatment was thawed at three different thawing rates: 25 °C for 30 sec, 30 °C for 16 sec and 40 °C for 12 sec. Motility, vitality and morphology analyses were performed by computer-assisted sperm analysis (CASA). The characteristics of the fresh sperm mostly resembled those found in the literature. For the parameters analyzed, fresh sperm presented higher sperm quality in comparison to all treatments with cryopreserved sperm (p < 0.05), except for the characteristic of normal morphology, for which the sperm cryopreserved in glucose and MG did not differ statistically from the fresh sperm. For the cryopreserved semen, the greatest results of total motility and curvilinear velocity (VCL) were obtained using glucose and DMSO, regardless of the thawing rate employed. For the straight-line velocity (VSL) and average path velocity (VAP), DMSO showed the best results, regardless of the diluent and thawing rate. With regard to vitality, the highest values were achieved when DMSO and thawing rates of 30 °C for 16 sec or 40 °C for 12 sec were used. In the morphological analysis, the greatest percentage of normal sperm cells was obtained using thawing rates of 25 °C for 30 sec and 40 °C for 12 sec, regardless of the freezing media. Sperm quality was found to suffer interference from the freezing media, as well as from interaction between its components (diluent and cryoprotectant) and the thawing rate used. Under the methodological conditions employed, the use of 5% glucose + 10% DMSO and a thawing rate of 30 °C for 16 seconds or 40 °C for 12 seconds is recommended for P. brevis semen cryopreservation.