Research Article: The effect of cryopreservative extender developed for Mesopotamian spiny eel (Mastacembelus mastacembelus Banks & Solander, 1794) on sperm motility and fertilization rate after thawing

This study was aimed to determine the effect of a freezing extender developed for Mesopotamian spiny eel (Mastacembelus mastacembelus Banks & Solander, 1794). Mesopotamian spiny eel was caught from May to July 2017 in the Atatürk Dam Lake and Euphrates Basin (meridians) in Şanliurfa, Turkey. During the study, the animals (n=10; 8 males, 2 females) were caught with gill nets (22 mm×22 mm, mesh size) and kept under natural lake water [temperature (22.00–23.60ºC), oxygen (8.45–8.98 mg/l), pH (8.14–8.50) and salinity (0.22 ppt)]. Semen was collected from eight males (406.46±166.68 g) weekly by abdominal massage after the hormonal injections of human chorionic gonadotropin treatment. Sexual maturation and spermiation of MSE males (n=8) were stimulated by weekly injections of human Chorionic Gonadotropin (hCG; Pregnyl, Merck Sharp Dohme, Turkey) [(1 International Unit (IU) hCG/body weight (g)/week]. At the 7th week of hormonal treatment, milt from eight mature males was carefully collected by abdominal massage, avoiding contamination with urine and feces into the petri dish, 24 h after the hormone applications. The motility of the collected spermatozoa and the spermatozoa density were evaluated on day of collection. Sixteen milliliter pooled ejaculate (2 milliliter per male) was split into two equal aliquots and diluted with the ArŞaDo extender (NaCl (163mM), NaHCO3 (9.4mM), MgCl2 (0.84mM), CaCl2 (8.26mM) and KCl2 (18.16 mM)) and the P1 (NaCl (125 mM), NaHCO3 (20 mM), MgCl2 (2.5 mM), CaCl2 (1 mM) and KCl2 (30 mM)) extenders. After two weeks, straws were thawed in a water bath at 40°C for 13 s and post-thaw sperm motility was immediately estimated subjectively. For the activation, saline solution (0.9% NaCl) was used. Sperm motility of thawing samples was significantly higher in ArŞaDo extender than in P1 extender (42.66±1.17% vs. 32.96±1.27%, respectively). The fertilization rate in ArŞaDo extender was higher than sperms preserved in the P1 extender (82.03±1.94% vs. 73.43±1.45%, respectively). In conclusion, the ArŞaDo extender improved the post-thawing spermatozoa motility percentage and fertilization rate in Mesopotamian spiny eel males.