Evaluate effects of the dilution medium and holding time on various motility parameters of delta smelt semen

Sperm preservation is an efficient technique used for the recovery, conservation, and management of some endangered fish species. The present study was conducted to explore how preservation time would affect sperm and spawning performance in the endangered delta smelt (Hypomesus transpacificus). Sperm were preserved with the modified Hanks balanced salt solution at 14.7-16.9 °C. The Kruskal-Wallis test of sperm parameters using OpenCASA plugin in ImageJ software showed that sperm (n = 33♂) had significantly higher velocity and motility within the first 5 s after activation than that of other time points, while sperm had the lowest velocity and motility after 3 min post activation (P < 0.001). The findings (n = 30♂) also showed fresh sperm had higher velocity and motility than preserved sperm, while the sperm preserved for over 24 h showed a significantly low performance (P < 0.001). The nonlinear mixed effects models of fertilization results (n = 14♂ × 70♀) indicated the fresh sperm and sperm preserved for 1 h had higher fertilization rates than other preservation times (P < 0.001). The hatching rate (n = 14♂ × 70♀) also showed the fresh sperm and sperm preserved for 3 min and 1 h had higher hatching rates than other preservation times (P < 0.001). Overall, the study showed the best sperm performance in delta smelt was found within the first 5 s post activation, and the best fertilization and hatching rates were found when the sperm were fresh and preserved for 1 h. The findings of this study provide information for the first time about how long the delta smelt's sperm are motile for quality analysis, and how the preservation time can affect sperm quality, fertility, and hatching of this species for future applications.