Effects of body size on biochemical characteristics of trabecular cardiac muscle and plasma of rainbow trout (Oncorhynchus mykiss)

The objective of this study was to characterize biochemical indices of oxid ative metabolism in trabecular cardiac muscle of female rainbow trout over a 200-fold size range. We also examined scaling effects on plasma concentra tions of protein, albumin, and non-esterified fatty acids (NEFA). Animals w ere sampled from four size categories (< 20 g, 100-200 g, 300-400 g and > 2 kg). Ventricle mass relative to body mass was size-dependent, with the sma llest trout having smaller hearts. Total protein in cardiac tissue was 20%, higher in animals weighing over 300 g compared to fish less than 200 g. Pl asma albumin and protein were increased 50-70% in trout over 100 g compared to fish smaller than 20 g. NEFA in plasma were similar for all animals. Ac tivities of carnitine palmitoyltransferase and cytochrome oxidase were elev ated 53% and 38%, respectively, in trabecular cardiac muscle of the largest trout compared to the smallest animals. Citrate synthase activity was inde pendent of heart size, suggesting that the increase in oxidative capacity w as not due to an increase in mitochondrial density. The increased capacity to bind and transport fatty acids in blood and the higher oxidative capacit y of cardiac muscle may reflect a metabolic adaptation for increased oxidat ion of fatty acids and ventricular performance in larger female trout. Thes e findings are not consistent with the scaling paradigm of oxidative metabo lism and may reflect changes in ventricular architecture with ontogeny. (C) 1999 Publised by Elsevier Science Inc. All rights reserved.