Spermatological characteristics and effects of cryopreservation in Lebranche mullet spermatozoa (Mugil liza Valenciennes, 1836): First report of ultra-rapid freezing

The present study investigated the spermatological characteristics of raw semen of Lebranche mullet (Mugil liza), namely pH, and sperm density, and motility; and subsequently evaluated the effects of different times of exposure to cryoprotectants, and the application of an ultra-rapid freezing protocol, on sperm motility and plasma membrane integrity. Semen samples were analyzed undiluted (control) and diluted 1:50 v/v in CF-HBSS + 10% Dimethyl sulfoxide + 30% Ethylene glycol + 94.58 gL-1 Trehalose dehydrate (n = 15). Two treatments - diluted semen samples in cryoprotective medium without ultra-rapid freezing (T1), and diluted semen in cryoprotective medium with ultra-rapid freezing (T2) - were evaluated at 0, 2, 4, 6 and 8 min. The frozen samples were thawed at 37oC for 60 s. The spermatological characteristics recorded for the semen were: pH: 7.57 +/- 0.21; sperm density: 30.4 +/- 2.9 x 109 sperm mL-1; motility: 82 +/- 4.9%. Sperm motility presented differences after 2 min exposure to cryoprotectants (70.0 +/- 2.7%) and ultra-rapid freezing (66.5 +/- 5.8%) compared to the control group (98.5 +/- 1.9% and 98.5 +/- 2.1%, respectively; p 0.05); however, differences were observed in the parameters evaluated after longer exposure and cryopreservation times. This is the first report evaluating the effects of different times of exposure to cryoprotectants and direct ultra-rapid freezing in liquid nitrogen on Mugil liza sperm. Our results demonstrated the protocol of sperm ultra-freezing is safe within a time ' s window of 2 min of exposure to cryoprotectants, after which a toxicity effect on sperm can be observed