Comparative study on the acrosin activity in sperm of the marine crab Charybdis japonica (A. Milne-Edwards, 1861) (Brachyura, Portunidae) under different environmental conditions

The optimal environmental conditions for acrosin activity in sperm ofCharybdis japonicawere assessed by orthogonal experiments, and the variation of the acrosin activity in sperm was analysed under hypothermic preservation at 4°C and cryopreservation in liquid nitrogen at −196°C, respectively. The acrosin activity and protein component in sperm from the female spermatheca and from the male seminal receptacle, were also compared. The highest acrosin activity was obtained at pH 8, 25°C and 30‰ salinity. The acrosin activity and viability rates of sperm decreased with the preservation time elapsed at 4°C, and a positive correlation between acrosin activity and viability rates (; ) was recorded. These two indices decreased significantly before and after cryopreservation at −196°C, and subsequently changed slowly in the liquid nitrogen. The cryoprotectant had a significant effect on the viability rates of sperm, but not much on the acrosin activity. The acrosin activity of sperm from the male seminal receptacle was (122.53 ± 1.66) × 10−6 μIU under optimal environmental conditions, which was significantly higher than that of the sperm from the female spermatheca (105.65 ± 2.91) × 10−6 μIU (). Three kinds of protein subunits in sperm acrosin from the male seminal receptacle were observed by dissociating SDS-PAGE (71.7, 69.2 and 67.3 kDa), which were degraded to some degree in the female spermatheca (70.4, 66.7 and 64.9 kDa). Several special components were noted in the female spermatheca, with one of higher molecular mass and five of lower molecular mass, which may play an important role in preserving the sperm in the female spermatheca.