Cell morphology as an indicator of viability of cod eggs - results from anexperimental study

This study evaluates the use of egg malformations, at early blastula stages , as direct indicators of egg viability in cod, Gadus morhua. Eggs with vis ible aberrations at early stages (4-32 cells) were incubated individually, using regular eggs as controls. Irregular eggs displayed, on an average, a lower hatching rate than the controls, 35% and 80%, respectively, but with substantial variation among batches. In several examples, severe malformati ons at blastula stages (4-32 cells) resulted in normal hatching. There were no differences in mortality rate during the yolk-sec period between larvae hatching from irregular eggs and controls, respectively, implying similar opportunities for further survival. In addition, artificially fertilized eggs of 17 batches from 11 different f emales of Baltic cod were incubated after estimations of malformation rate at early blastula stages. Viable hatch varied between 14% and 97% (average 64%, SD=28) among batches and a rank correlation test revealed a significan t correlation between malformation rate (average 13%, SD=17) and viable hat ch. The results are consistent with those from the individual egg incubatio n, suggesting that malformations during early stages may affect further dev elopment. However, large variations in hatching success, between batches, b oth from individual egg incubation and from incubation in batches indicate that other factors may be important. This study reveals that severe aberrat ions occurring at early stages may recover. Thus, malformations occurring a t early blastula stages should be used with prudence and not as a direct an d consistent indicator of poor egg viability. (C) 1998 Elsevier Science B.V . All rights reserved.