Sperm motility patterns of Atlantic cod (Gadus morhua) in relation to salinity: effects of ovarian fluid and egg presence

A significantly greater proportion of Atlantic cod (Gadus morhua) sperm were motile in the presence of ovarian fluid and egg compared with seawater. Sperm mean and maximum swimming speeds were also significantly greater in the presence of ovarian fluid and egg compared with seawater. However, there was no significant difference in path linearity among treatments. We also examined the interaction between maternal stimuli (egg and ovarian fluid), time sperm spent in seawater prior to exposure to each stimulus, and salinity on proportion of motile sperm and their swimming behaviours. Proportion of motile sperm decreased significantly with a decrease in salinity in the presence of both maternal stimuli. Proportion of motile sperm also decreased with time spent in seawater prior to exposure to ovarian fluid but not to an egg. Both mean and maximum swimming speeds were maintained in the salinity range of 20-30 ppt and only declined significantly at lower salinities (15 and 17.5 ppt). Mean and maximum swimming speeds decreased with time spent in seawater. This study demonstrates the importance of maternal factors when examining sperm swimming behaviour and highlights the significance of maternal-paternal gametic interactions in understanding fertilization success.