Concentration and Location of Metabolic Substrates in Fast Toadfish Sonic Muscle

Abstract

We measured glycogen, lipid and water concentrations in toadfish (Opsanus tau) fast sonic muscle and white body muscle, and glycogen and lipid were localized histochemically in the sonic muscle. Sonic muscle had 5.05 jg of glycogen per mg wet weight, 15.64% fat and 81% water. These values were 2.2, 6.2 and 0.18 times higher than the corresponding concentrations in white body muscle. The presence of abundant glycogen and fat provides potential fuel for anaerobic and aerobic metabolism and agrees with the designation of sonic muscle as fast oxidative glycolytic. No sexual or ontogenetic differences were present in glycogen, fat or water concentrations in sonic or body muscle, and these molecules cannot be used to explain sexual differences in sound production. Glycogen is localized in sarcoplasm under the sarcolemma, in sarcoplasmic reticulum and throughout the sarcoplasmic core. Lipids have a similar distribution, except that their distribution in the core is restricted to the periphery. These findings are in accord with ultrastructure of sonic muscle fibers.