Temperature-dependent development rates of cod Gadus morhua eggs

Temperature development relationships were determined for batches of Irish Sea cod Gadus morhua eggs incubated in flow-through incubators. Hatching began 16.4 days after fertilization (DAF) at 6 degrees C, 10.3 DAF at 8 degrees C, 9.4 DAF at 10 degrees C and 7.4 DAF at 12 degrees C. Egg mortality increased at the higher temperatures, but survival was > 80%. Results were compared with published data at four comparable stage end points: the end of blastula, the end of gastrula, the point of growth of the embryo completely surrounding the yolk and the point when 50% of the eggs were hatched. All the studies showed a curvilinear relationship between age at stage and temperature. There was a 12 day inter-study difference in time to 50% hatch at 2 degrees C and 4 day difference at 10 degrees C. There were no consistent trends that differentiated eastern v. western, or northern v. southern populations. A single model for cod egg incubation time from fertilization to 50% hatch was derived based on data from six cod populations, but it is recommended that individual stock relationships should be used where possible. (c) 2006 The Authors Journal compilation (c) 2006 The Fisheries Society of the British Isles.