Predicting
haddock embryo viability based on early cleavage patterns
R.M. Rideout, E.A. Trippel, M.K. Litvak-2004
Aquaculture, 230(1-4): 215-228
Abstract:
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.
(Fisheries
and Oceans Canada, Biological Station, 531 Brandy Cove Road, St. Andrews,
NB, Canada E5B 2L9, e-mail: rideoutr@mar.dfo-mpo.gc.ca)