Sensitivity of grouper Epinephelus coioides eggs to handling stress at different stages of embryonic development

Abstract

The sensitivity of grouper Epinephelus coioides eggs to handling stress at different stages of embryonic development was investigated. Naturally-spawned grouper eggs in floating net cages were collected and handled at the early cleavage, blastula, gastrula, neurula, and eyed stages. Egg viability, hatching rate and percentage of normal larvae were significantly higher (p<0.05) in eggs collected and stocked at the eyed stage than in all other stages. An increasing sensitivity to handling stress was observed in eggs from early cleavage to gastrula, as manifested by the decreasing percentage of viable eggs, hatched, and normal larvae. Sensitivity to handling stress decreased when development reached the neurula and eyed stages. Hatched larvae from eggs handled during the blastula and gastrula stages had high mortalities during the first 3-24 hours after stocking. The results of this study show that grouper E. coioides eggs are most sensitive to handling stress during the early cleavage to gastrula phases. The results imply that harvesting or collection of grouper eggs is best done after neurulation, when the embryo has already formed optic vesicles (eyed stage), to increase egg viability and the hatching rate. It will also minimize mortalities and the occurence of abnormal larvae.