Evaluation of fast green uptake as a simple fitness test for spat of Perna canaliculus (Gmelin, 1791)

The method described here gauges marine mussel (Perna canaliculus) spat health by observing their declining ability to isolate themselves from hyposmotic water after exposure to apparently deleterious agents such as exposure to air, elevated temperature, and ethanol. This inward movement of water is disclosed by Fast Green stain. Although individual spat were found to stain either markedly or not at all, test groups showed variation in proportions staining with different treatments thus giving an indication of group (n = 50) fitness. Control and lethally stressed spat groups showed low and high staining proportions, respectively, that corresponded with group differences (P < 0.001) in physical activity and valve closure in freshwater. Furthermore, staining and activity levels in a range of spat samples from controls to lethal exposures show a highly significant correlation (r = − 0.967, P < 0.001). Thus staining is a good surrogate for activity as an indicator of group health. The advantage of staining over activity assessment is its ease and brevity. A range of conditions caused by exposure to air, ethanol and nutrient loaded (hypoxic) water were detectable (P < 0.05): normal health, sublethal and lethal conditions were statistically distinguishable. Such a test may have application in the mussel industry as currently there is no quick means of testing spat viability. This is needed because spat at this stage are commonly distributed from nursery or wild settlement site to grow-out locations; different handling and transport regimes may impact on spat viability. Successful grading and ensuing pricing based on viability will encourage best practice in maximizing spat quality thereby extending a currently limited spat supply.