Ontogenetic patterns and temperature-dependent growth rates in early life stages of Pacific cod (Gadus macrocephalus)

Pacific cod (Gadus macrocephalus) is an important componentof fisheries and food webs in the North Pacific Ocean and Bering Sea. However, vital rates of early life stages ofthis species have yet to be described in detail. We determined the thermal sensitivity of growth rates ofembryos, preflexion and postflexion larvae, and postsettlement juveniles. Growth rates (length and mass) ateach ontogenetic stage were measured in three replicate tanks at four to five temperatures. Nonlinear regressionwas used to obtain parameters for independent stage-specific growth functions and a unified size- and temperature-dependent growth function. Specific growth rates increased with temperature at all stages and generallydecreased with increases in body size. However, these analyses revealed a departure from a strict size-basedallometry in growth patterns, as reduced growth rates were observed among preflexion larvae: the reduction in specific growth rate between embryos and free-swimming larvaewas greater than expected based on body size differences. Growth reductions in the preflexion larvae appear to be associated with increased metabolic rates and the transition from endogenous to exogenous feeding. Infuture studies, experiments should be integrated across life transitions to more clearly define intrinsic ontogenetic and size-dependent growth patterns because these are critical for evaluations of spatial and temporalvariation in habitat quality.