Parr-Smolt Transformation of Atlantic Salmon (Salmo salar): Activities of Two Respiratory Enzymes and Concentrations of Mitochondria in the Liver

Abstract

Hatchery-reared parr and smolts of Atlantic salmon (Salmo salar) derived from spawners of the Big Salmon, Saint John, and Penobscot rivers were analyzed for activity of two respiratory chain enzymes in liver. Cytochrome c oxidase activity was about 15-fold greater in enzyme units than succinate dehydrogenase in all three experimental groups. Smolt sample means for cytochrome c oxidase and succinate dehydrogenase in Big Salmon and Saint John fish were significantly greater than those of parr. Measurements in Big Salmon fish, which had the greatest parr–smolt difference in cytochrome c oxidase units and condition factor, demonstrated a significantly greater smolt sample mean for liver mitochondria concentrations. The results are discussed primarily in relation to the possible role of thyroid hormone in causing a greater potential for aerobic energy generation in liver during smoltification and the utilization of lipid as an energy resource.