The role of temperature on the growth and survival of early and late hatching Pacific cod larvae (Gadus macrocephalus)

Fish larvae hatch asynchronously from egg batches despite experiencing a common environment during their development. The consequences for growth and survival of early and late hatching larvae were examined in pre-feeding Pacific cod larvae under varying temperatures (i.e. 0-8 degrees C) in the laboratory. As expected, time-to-first hatch and variation in time-to-hatch were negatively correlated with temperature. Larvae successfully hatched in the 0 degrees C treatment, but hatch rates were poorer at this temperature relative to other temperature treatments. Size-at-hatch and the maximum size achieved during the pre-feeding larval stage were highest in the 0-4 degrees C treatments, indicating that these temperatures are likely optimal for the conversion of endogenous resources to growth. At all temperatures, early hatching larvae were smaller but had more lipid reserves and survived longer after hatch in the absence of food than late hatching larvae. Together these data suggest that temperature fluctuations in the North Pacific have direct potential to impact the size, growth and endogenous reserves of Pacific cod larvae, which in turn, will likely influence survival through interactions with the prey and predator field.