Effect of freezing and thawing rates on sperm motility in Bocachico Prochilodus magdalenae (Pisces, Characiformes)

Objective. To determine the freezing and thawing rates necessary to maintain sperm viability during cryopreservation of Bocachico semen. Materials and methods. Four interactional treatments were implemented between two freezing (rapid and slow) and two thawing (rapid and slow) curves, in a 2x2 factorial as follows: rapid freezing-rapid thawing, rapid freezing-slow thawing, slow freezing-rapid thawing, and slow freezing-slow thawing. After thawing by Sperm Class Analyzer (SCA) curvilinear velocity (VCL) and straight-line (VSL) (ìm sec-1) were analyzed; total, rapid, medium, and slow motility, were compared among treatments. Results. The rapid freezing-slow thawing treatment was lethal for all variables of velocity and motility, causing a significant (p<0.01) post-thaw inmotility of 100%. The slow freezing-rapid thawing interaction had a significantly higher effect than the other treatments (p<0.05), particularly on variables such as rapid motility (10.1 ± 1.1%), medium motility (30.16 ± 4.1%), and curvilinear velocity (51.5 ± 4.75 ìm sec.-1) also decreased the percentage of sperm with slow motility (41.7 ± 4.45%). Independently of the applied thawing rate, the freezing rate generated the main significant effect on total motility. Conclusions. It is possible to conclude that the interaction effect between freezing and thawing rates is nil (except for slow motility) during cryopreservation process. However, the independent effects of these factors (main effects) on remaining motility variables are positively significant and decisive to the maintenance of these features, especially the freeze factor (when it is slow). This becomes the first successful report of sperm cryopreservation from Bocachico Prochilodus magdalenae in the world and may be used in conservation programs for this endangered species.Objetivo. Determinar la tasa de congelacion y descongelacion para mantener la viabilidad espermatica durante la crioconservacion seminal de Bocachico. Materiales y metodos. Fueron implementados cuatro tratamientos de interaccion entre dos curvas de congelacion (rapida, lenta) y dos curvas de descongelacion (rapida, lenta) en un factorial 2x2, asi: congelacion rapida-descongelacion rapida, congelacion rapida-descongelacion lenta, congelacion lenta-descongelacion rapida y congelacion lenta-descongelacion lenta. Posterior a la descongelacion espermatica y mediante el software Sperm-Class-Analyzer, fueron analizadas la velocidad curvilinea (VCL) y lineal (VSL) (Êm sec-1); movilidad total, rapida, media y lenta, y fueron comparadas entre tratamientos. Resultados. El tratamiento congelacion rapida-descongelacion lenta fue letal para las variables de velocidad y movilidad espermatica, causando una significativa (p<0.05) inmovilidad pos-descongelacion (100%). La interaccion congelacion lenta-descongelacion rapida tuvo un efecto significativamente mejor (p