Our goal is to develop a strain of yellowtail Seriola quinqueradiata that exhibits economically desirable traits using genome editing. To prevent deaths caused by sinking of yellowtail eggs before hatching and develop a small container incubation method to rear the small number of eggs obtained by microinjection, we first determined the specific gravity of eggs and identified appropriate salinities for hatching. Then, we measured the hatching rates of eggs microinjected with GFP-mRNA and incubated at the appropriate salinities. The specific gravity of eggs increased during development, exceeding that of sea-water 5 h before hatching. Normal hatching rates (i.e., excluding abnormal larvae) ranged from 0-94.8. at salinities of 30-60 psu, and were >80. at those of 35-40 psu. The normal hatching rate of microinjected eggs kept at 40 psu was significantly lower (7.4%) than that at 35 psu (56.7%). The normal hatching rate of microinjected eggs at 35 psu was 80% similar to that of non-injected eggs at 35 psu. Thus, we can control hatching rates of microinjected yellowtail eggs in small containers using sea-water adjusted to 35 psu.
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