Cost and efficiency of growth in the larvae of two species of fish with widely differing metabolic rates

This investigation was designed to test two hypotheses. First, does the proportional relation between rate of growth and rate of oxygen consumption in excess of maintenance, demanded by classic nutrition physiology, apply to small poikilotherms growing at 20% of body mass per day and faster? Secondly, to what extent are net and gross efficiencies of growth affected by the level of metabolic power? The metabolic rates of the coregonid species, Coregonus wartmanni (L.), exceeded the metabolic rates of the cyprinid species, Rutilus rutilus (L.) by a factor of 1.5-2.0. Relative growth rate (g, in% DBM per day) and oxygen consumption in excess of maintenance (= feeding-induced thermogenesis: FIT, in $\mu $mol g$^{-1}$h$^{-1}$) were related by the regression: FIT = 3.81($\pm $1.4)+1.05($\pm $0.15) g up to approximately 8% per day, whereas at faster growth FIT remained constant at 12.4$\pm $1.4 $\mu $mol g$^{-1}$h$^{-1}$ in both species. Thus an aerobic maximum for growth can be defined that is independent of the rate of growth between about 8 and 16% per day, at 15 degrees C Although up to about 80% per day the net cost ofgrowth is identical in the two species investigated, the net efficiency of growth is quite different; for g = 1% per day it is 2.9% of the maximum rate of metabolism in C. wartmanni, but 4.4% in R. rutilus.