Direct Evidence for Functional and Metabolic Differences between Dark and Ordinary Muscles in Free-swimming Yellowtail, Seriola quinqueradiata

Abstract

In order to correlate function of dark and ordinary muscles directly with metabolic activity by measuring the electrical activity and changes in blood lactate concentration simultaneously in free-swimming yellowtail in the water tunnel, a polyethylene cannula for blood sampling and three pairs of electrodes for electromyography were implanted in each fish weighing 600–900 g. Ordinary muscle showed electrical activity only during vigorous swimming at high speed, when no more than 10 min swimming caused a sharp increase in blood lactate concentration. On the other hand, in the recordings from dark muscle, relatively rhythmical burst of discharge was observed corresponding to each tail beat at any swimming speed. During moderate swimming at low speed when orJy dark muscle was active, there was no change in blood lactate concentration, even though the fish was forced to swim for 1–3 h. Therefore, the accumulation of lactate does not seem to be caused by dark muscle activity, but caused by ordinary muscle activity. During burst or vigorous movement, energy seems to be supplied largely from anaerobic metabolism in ordinary muscle and during cruising or moderate swimming from aerobic metabolism in dark muscle. © 1981, The Japanese Society of Fisheries Science. All rights reserved.