Effects of Gonadal Suspensions of Disk Abalone Haliotis discus discus on Egg Laying, Sperm Release, and Fertilization Rate

Marine organisms often respond to chemical cues released by conspecifics, and such cues can trigger reproductive behavior. In abalone, gamete release by one individual may stimulate spawning in nearby individuals. In this study, gonadal suspensions prepared from the ovaries and testis of disk abalone Haliotis discus discus were incubated for approximately 1 h at different temperatures and then exposed to sexually mature individuals to evaluate their egg-laying- and sperm-release-inducing activity, as well as the quality of the resulting gametes. Suspensions incubated at room temperature (20 ± 0.3°C) or at 40°C generally retained their egg-laying- and sperm-release-inducing activity relative to freshly prepared suspensions. However, egg-laying-inducing activity of the ovarian suspension in females appeared to begin to decline at 40°C, although the difference from the control was not statistically significant (p = 0.086). Overall, the inducing activity of the gonadal suspensions decreased sharply at 50°C, at which egg laying and sperm release were significantly reduced. However, when gametes obtained after exposure to the gonadal suspensions were artificially fertilized, fertilization rates did not differ significantly among treatment groups. These results indicate that incubation temperature had little effect on subsequent fertilization success. In contrast, the gamete-release-inducing activity of components present in the gonadal suspensions was sensitive to heating, with a marked decline at 50°C. The findings provide insight into the thermal sensitivity of gamete-release-inducing activity in abalone gonadal suspensions and may contribute to a better understanding of chemical communication during reproduction in marine invertebrates.