Predicting haddock embryo viability based on early cleavage patterns

Haddock, Melanogrammus aeglefinus, is a serial spawning, marine gadid characterized by low survivorship during the early life history stages. The potential for predicting future survival to hatching based on cleavage patterns of early embryos (8–32 blastomere stages) was investigated in order to improve efficiency of early rearing practices. In 2001, data from 36 egg batches (>95% fertilization) suggested that hatching success was inversely related to the percentage of embryos with abnormal cleavage. Mean percentage of normal cleavage did not differ throughout the spawning season but variability was much higher for embryos from early and late batches than those collected during the middle of the spawning season. In 2002, abnormalities in blastomere cleavage for 12 egg batches were further categorized as (1) asymmetric blastomere arrangement, (2) inequality of blastomere size, (3) poor adhesion between blastomeres and (4) poor definition of blastomere margins. Results suggested that all four abnormalities were co-occurring, which prevented negative effects on hatching success from being attributed to a single abnormality. Incubation of embryos with only one type of cleavage abnormality suggested that low adhesion between blastomeres significantly reduced embryo viability, while asymmetry in blastomere arrangement did not. However, because cleavage abnormalities tended to co-occur, hierarchical multiple regression revealed that asymmetry could be used to accurately predict hatching success, even if reduction in embryo viability was due to abnormalities other than asymmetry. Analysis of additional cleavage abnormalities suggested that complete separation between blastomeres was indicative of a very poor egg batch and resulted in little or no hatching, while cellular outcrops had no negative effect on hatching success. Information from detailed studies such as these could be used to predict hatching success of individual egg batches, allowing time and resources to be allocated more efficiently in hatcheries.