On the muscular fuel of the air sac in an air breathing fish.

The hyohyoideus muscle which is responsible for inflating and contracting the air sac in an air breathing fish, Amphipnous cuchia, belongs to white fibre type as it lacks muscle myoglobin. The muscle shows appreciable amount of glycogen and extracellular phospholipid globules. Staining of I bands in the muscle fibres with Alcian blue (1.0 less than or equal to pH less than or equal to 3.0) indicates presence of acid mucosubstances. The muscle does not show change in phospholipid content at the histochemical level but lowering of glycogen content (25 to 30%) when put to 51/2h of continuted physiological exercise. At the same time, increase in blood sugar level (20 to 30%) possibly indicates utilization of glycogen as the source of energy by the muscle. However, a clear cut priority of glycogen or phospholipid break down for energy source by the muscle could not be established.