Evaluating spawning induction methods for the tropical black-lip rock oyster, Saccostrea echinata

Abstract

When developing a species-specific hatchery protocol it is important to investigate the triggers for spawning, which is the foundation of the production cycle. This study evaluated multiple spawning induction techniques to optimise the spawning success of black-lip rock oyster, Saccostrea echinata, broodstock. Initially, the most effective method for non-destructively opening broodstock was determined, to allow intramuscular injection of chemical stimuli. Following this, the efficacy of seven spawning induction treatments, including two physical shock techniques, three chemical induction techniques, a combination of physical and chemical induction and strip spawning were assessed. Based on the outcomes of these trials, the combined and independent effects of reduced salinity and addition of sperm, as well as the potential of neuropeptides to trigger spawning, were evaluated. Results demonstrated that a concentration of 30 g/L of MgCl2 is an effective muscle relaxant for commercial and research application for S. echinata. It was determined that salinity reduction, rather than temperature increase, is a key factor for spawning induction. Strip spawning is a viable option for S. echinata; however, sperm motility was significantly affected, and fecundity and fertilisation rates were lower (although not significant, P > 0.05) when compared to other induction methods tested. A combination of physical and chemical induction, involving reduced salinity and addition of sperm, was the most successful treatment; 80 % of broodstock spawned within 19 min of salinity drop and addition of sperm. This method delivers significant production improvements for S. echinata, particularly regarding the time taken to induce spawning, and is therefore recommended for application in the hatchery.