Blastomere morphology as a predictive measure of fish egg viability

• Published in: Aquaculture 1997-09, Vol.155 (1), p.1-12
• Main Authors: Shields, R.J., Brown, N.P., Bromage, N.R.
• Format: Article
• Language: English
• Subjects: Aquaculture; Blastomeres; Cleavage; Fish; Fish eggs; Fish hatcheries; Freshwater; Hippoglossus hippoglossus; Marine; Viability
• ISSN: 0044-8486; 1873-5622
• DOI: 10.1016/S0044-8486(97)00105-1

For most fish species, blastomere size and shape are uniform during normal cleavage. However, abnormal blastomere morphology has been observed in a variety of studies, either induced directly by chemical or physical Stressors, or observed in eggs collected from plankton or broodstock. It has been proposed that abnormalities are indicative of low egg viability and may provide a useful predictive tool for egg assessment. However, there is little direct evidence relating blastomere morphology to egg survival. This paper reviews the literature on abnormal embryonic development in fish, and presents new findings on the significance of blastomere morphology in the Atlantic halibut, Hippoglossus hippoglossus. Several studies have reported qualitative relationships between egg batch survival and the proportion of normal embryos for a variety of fish species. In order to investigate more closely the relationship between blastomere morphology and fish egg survival, incubation experiments where carried out with eggs of Atlantic halibut. Eggs were individually assessed at the 8-cell stage for 5 blastomere characteristics and incubated to hatch in multiwell microtitre plates. For data pooled from 13 egg batches, the mean score for each blastomere characteristic showed a significant positive linear regression with the number of eggs hatched. Multiple regression analysis, incorporating all five blastomere characteristics, demonstrated a high degree of correlation between the independent variables. While the experimental procedure that was used for halibut eggs is too laborious for routine hatchery application, it is proposed that subjective observations of blastomere morphology could be readily adopted by commercial hatcheries to provide early assessment of egg viability.