THE EGG SENSITIVITY AT DIFFERENT DEVELOPMENTAL STAGES OF SILLAGO JAPONICA TO THERMAL SHOCK, DROP SHOCK AND ULTRAVIOLET IRRADIATION

In this study, the normal embryonic development of Sillago japonica egg was divided into 27 stages from fertilization to hatching. The sensitivity of eggs to thermal shock, drop shock and ultraviolet irradiation at each developmental stages were compared. Elevation of temperature greatly affects the development particularly during two periods, the early cleavage stage and the stage of late gastrula to closure of blastopore. Drop shock sensitivity during late cleavage to appearance of embryo was higher than that in the other stages. However,in the case of ultraviolet irradiation, the stage of appearance of embryo revealed the highest sensitivity. In this paper, the reasons for the different effects observed at similar developmental stages on the fish egg were described, and suggestion for avoiding these environmental effects on fish eggs at their higher sensitivity developmental stages was also made for the protection of fisheries resource and process of egg incubation.