BLASTOMERE MORPHOLOGY AS A PREDICTIVE MEASURE OF FISH EGG VIABILITY

For most fish species, blastomere size and shape are uniform during no rmal cleavage. However, abnormal blastomere morphology has been observ ed in a variety of studies, either induced directly by chemical or phy sical stressors, or observed in eggs collected from plankton or broods tock. It has been proposed that abnormalities are indicative of low eg g viability and may provide a useful predictive tool for egg assessmen t. However, there is little direct evidence relating blastomere morpho logy to egg survival. This paper reviews the literature on abnormal em bryonic development in fish, and presents new findings on the signific ance of blastomere morphology in the Atlantic halibut, Hippoglossus hi ppoglossus. Several studies have reported qualitative relationships be tween egg batch survival and the proportion of normal embryos for a va riety of fish species. In order to investigate more closely the relati onship between blastomere morphology and fish egg survival, incubation experiments where carried out with eggs of Atlantic halibut. Eggs wer e individually assessed at the 8-cell stage for 5 blastomere character istics and incubated to hatch in multiwell microtitre plates. For data pooled from 13 egg batches, the mean score for each blastomere charac teristic showed a significant positive linear regression with the numb er of eggs hatched. Multiple regression analysis, incorporating all fi ve blastomere characteristics, demonstrated a high degree of correlati on between the independent experimental procedure that was used for ha libut eggs is too laborious for routine hatchery application, it is pr oposed that subjective observations of blastomere morphology could be readily adopted by commercial hatcheries to provide early assessment o f egg viability. (C) 1997 Elsevier Science B.V.