Changes in Specific Gravity of Eggs of the Blacktip Grouper Epinephelus fasciatus during Embryonic Development

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The specific gravity of the blacktip grouper Epinephelus fasciatus eggs was measured in a series of saltwater solutions of different specific gravity. In this study, the specific gravity of the eggs was inferred from the neutral buoyancy salinity (NBS), defined as the lowest salinity in which 80% or more of the eggs remained above mid-depth. The NBS was approximately constant at 30.4-30.9 PSU (=1.0224-1.0229 g/cm3 in density at 15°C) from one-cell stage to appearance of kupffer's vesicle stage and gradually increased through the later stages. The maximum NBS (35.8 PSU (=1.0266 g/cm3) ) was observed just before hatching. Because the NBS just before hatching was denser than that of rearing saltwater (34.8 PSU (=1.0258 g/cm3) ), eggs sank to the bottom of the tank. Thus, the management of eggs just before hatching is important for larval production. Inparticular, it is necessary to provide adequate levels of aeration and water circulation to prevent eggs from sinking.
日本水産増殖学会の論文