Aquaculture Reports (Dec 2024)
Impact of salinity and body size on sperm motility in three California smelt species
Abstract
Three smelt species in California, USA—the endangered delta smelt Hypomesus transpacificus and longfin smelt Spirinchus thaleichthys and the introduced wakasagi H. nipponensis—experience ecological pressures, including habitat alterations, temperature changes, and fluctuating salinity levels that can affect their survival and reproductive success. The present study investigates how salinity during the spawning process influences sperm motility by analyzing 13 sperm motility traits across three salinity levels (0.4, 5, and 10 ppt). Using Principal Component Analysis, we found that the first two principal components accounted for over 65 % of the total variance. Consequently, two predominant traits from each principal component were selected to evaluate sperm motility. Specifically, the amplitude of lateral head displacement (ALH), linearity coefficient (LIN), curvilinear velocity (VCL), progressive motility (PM), and wobble coefficient (WOB) predominantly contributed to these components for both longfin smelt and wakasagi. Results showed that the salinity significantly impacts these traits, except for ALH in delta smelt and longfin smelt, and WOB and LIN in wakasagi. In addition, we found the salinity and temperature difference between the activating water and extender interact differently across species. In delta smelt, interactions between the activating water and extender temperatures significantly affected most traits, whereas in wakasagi, only the interaction between activating water salinity and extender temperature showed significant effects. No significant influence from these interactions was observed in longfin smelt. Additionally, the impact of body size (e.g., fork length) on sperm motility varies across species, with a significant influence observed in longfin smelt, while no effect was detected in delta smelt and wakasagi. Future research should focus on exploring the physiological mechanisms behind the observed effects of salinity, temperature, and body size on sperm motility, as well as examining these interactions in other species to develop broader conservation strategies under changing environmental conditions.
