Cryopreservation of Mesopotamian catfish (Silurus triostegus H., 1843) spermatozoa: Effects of diluents and osmotic pressure on spermatozoa DNA damage, rate and duration of motility

This study was performed to evaluate the effectiveness of three different conditions of osmotic pressure (325, 365 and 385 mOsm kg-1) in combination with dimethyl sulfoxide (DMSO) and NaCl or glucose on spermatozoa DNA damage, rate and duration of motility. Sperm was collected from eight healthy mature Mesopotamian catfish, evaluated microscopically and pooled at 25 °C. The pooled sperm samples were diluted to a final concentration of 1/3 (sperm/diluents) in  NaCl and glucose based extender (10% cryoprotectant and 10% egg yolk (EY) into 80% diluents) and separated into groups of 3 different osmotic pressures (325-365-385 mOsm kg-1). Equilibrated sperm was frozen in 0.25 mL straws. Sperm samples were tested for post-thaw sperm motility, duration of motility, DNA damage, and apoptotic index. The highest spermatozoa motility rates were obtained with glucose and NaCl diluents at osmotic pressures of 365 and 385 mOsm kg-1 (p<0.01). The spermatozoa motility duration was found to be the highest in glucose and NaCl diluents at 365 mOsm kg-1 osmotic pressure (p<0.01). The post-thawing live spermatozoa rate was determined to be the highest in the sperm frozen with glucose at 385 mOsm kg-1. The apoptotic cell rate was determined to be the highest in the sperm frozen with glucose at 385 mOsm kg-1 osmotic pressure. The necrotic cell rate was found to be the highest with 2.08±0.39% when frozen with the glucose diluent at 325 mOsm kg-1 pressures. It is concluded that the glucose solution with low osmolality had a harmful effect on the spermatozoa.