HUNT VON HERBING, I: Growth in the fast lane: metabolic scaling and activity in developing fishes.

Embryonic and larval growth rates are high(50% d,^-1)in some species,while juveniles have growth rates of 1-6%d^-1.Given finite energy supplies,how can embryos and larvae simultaneously maintain high growth rates,swim and perform other metabolic processes? High growth rates are costly as recent studies have found that metabolic rate scaled isometrically(b=1.0),not allometrically (b< 1.0),with mass in some fish larvae.But,these studies ignored the effect on metabolism of swimming activity, because it is so difficult to measure in larvae.This study measured growth rates and determined how metabolic-mass relationships change with activity and throughout ontogeny,in Atlantic cod.In conjunction with metabolic measurements,routine and maximal speeds, as well as the proportion of time spent resting, were recorded and analyzed using video and image analysis techniques. All metabolic comparisons were made at routine speeds, which comprised over 80% of the total activity. Growth rates were highest in embryos(15%d^-1),decreased to 8%d^-1 in larvae and were lowest in juveniles(1-4% d^-1),while metabolic rates increased steadily with body size and developmental stage.In contrast,metabolic intensities followed a parabolic pattern, increasing from the embryonic stage to a peak 50% of the way through the larval stage,then decreasing to very low juvenile values. Relationships between metabolic rate and mass changed throughout ontogeny;the relationships were non-significant in embryos, were isometric in yolk-sac larvae and were allometric in exogenous feeding larvae and juveniles. Ontogenetic changes in metabolism mass relationships were strongly influenced by body size and developmental stage,and both of these factors also influenced the relative energetic costs between swimming and growth.