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 × 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). On the other hand, the plasma membrane integrity of the spermatozoa after 2 min exposure to cryoprotectants (64.0 ± 8.6%) and ultra-rapid freezing (62.5 ± 5.2%) presented no differences compared to the control group (69.5 ± 3.9% and 70.0 ± 3.5%, 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.

Sperm characteristics of wild and captive lebranche mullet Mugil liza (Valenciennes, 1836), subjected to sperm activation in different pH and salinity conditions.

In this article we describe basic aspects of the sperm biology of lebranche mullet (Mugil liza) in the wild and in captivity, in particular assessing the effects of salinity (0, 10, 20, 30, 35, 40, 50 and 60 g L-1) and pH (6, 7, 8, 9 and 10) on sperm motility. Our results indicate that the highest percentage of motility was recorded with salinity 34.6 g L-1 (95 ±â€¯10%) and the longest motility time was obtained with a salinity of 34.8 g L-1 (189 ±â€¯15 s). Variations in the salinity between 30 and 35 g L-1 did not produce any significant alterations in sperm motility; however salinities of 20 and 50 g L-1 produced a significant loss of sperm motility. The highest percentage of motility was obtained at pH 8.5 (93 ±â€¯12%), and the longest motility period at pH 8.7 (218 ±â€¯13 s), while pH lower than or equal to 7 and equal to 10 both produced a significant loss in sperm motility. A positive correlation was found between pH/salinity and the motility percentage (R2 = 0.94 and R2 = 0.97) and motility time (R2 = 0.86 and R2 = 0.98). In seminal and morphometric parameters, statistically significant differences were observed in semen volume, sperm density, plasma membrane integrity and sperm morphometry between the groups studied, showing that the characteristics of the fish have a direct influence on sperm quality. The information generated in this research will be useful for developing biotechnology tools for the effective management of Mugil liza gametes.