Metabolic responses of striped bass (Morone saxatilis) to temperature acclimation. II. Alterations in metabolic carbon sources and distributions of fiber types in locomotory muscle

The effects of temperature acclimation on (1) fiber‐type distribution, and (2) alternate metabolic fuels for energy supply within different skeletal muscle fiber types in striped bass (Morone saxatilis) were examined. Histochemical analysis demonstrated an increase in the proportional cross sectional area of oxidative red fibers from 9.03% to 15.03% during cold acclimation (25°‐5°C). The rate of oxygen consumption was 1.78 times greater in red muscle than white in 25°C acclimated fish. This ratio increased to 2.32 in 5° fish. Oxidation of both 14C‐U‐glucose and 14C‐1‐palmitate was significantly greater in red muscle than in white at both acclimation temperatures. A lack of thermal compensation for metabolism of 14C‐U‐glucose was exhibited by both fiber types. Red muscle showed a dramatic increase in rate of 14C‐1‐palmitate oxidation after cold acclimation. Activities of glycolytic enzymes confirmed a high glycolytic capacity in white muscle; glycolytic capacities were dependent on acclimation temperature in both fiber types. Only red muscle showed a positive compensation for activities of key enzymes from aerobic metabolism. The results indicate an increasing reliance on aerobic metabolism of fat in the swimming musculature at cold acclimation temperatures. The capacity for sustained swimming under these conditions is conserved by (1) an increase in the relative proportion of red fibers, and (2) an enhanced capacity for energy supply in the red muscle by oxidative metabolism of stored lipid.