Comparative histochemical study of the succinic dehydrogenase (SDH) activity in the respiratory muscles of an air-breathing siluroid fish, Clarias batrachus (Linn.).

1. Funcitonal morphology including origin, insertion, innervation and action of the respiratory muscles in relation to the respiratory pumps and the movement of barbels and gill filaments have been studied in a fresh-water air-breathing siluroid fish, Clarias batrachus (Linn.). 2. Cytochemical studies were made on the succinic dehydrogenase (SDH) activity of:--Abductor hyomandibularis, Adductor arcus palatini, Adductor hyomandibularis, Adductor mandibularis, Intermandibularis anterior and posterior, Interhyoideus, and Rectus cervicis (all concerned with buccal pressure pump), Adductor operculi, Dilator operculi, Levator operculi, Inferior hyohyoideus, Superior hyohyoieus (all concerned with opercular suction pumps), Extensor tentaculi, Protractor tentaculi, Retractor tentaculi (movement of barbels), adductor and abductor muscle sheets of the Constrictor branchialis (movement of gill filaments). 3. The intensity of SDH reaction reveals that except the Adductor mandibularis, Intermandibularis anterior and the Protractor tentaculi all muscles are made up of red as well as white muscle fibers. 4. The muscle innervated by the branches of Vth (trigeminal) nerve is dominated by white fibres, whereas those innervated by the branches of VIIth (facialis) contain more red muscle fibres. 5. The Retractor tentaculi (concerned with the movement of maxillary barbel) consists of superficial white fibers and its interior deeper part is dominanted by red and intermediate muscle fibres. 6. The adductor muscle sheet of the Constrictor branchialis is made up of red fibres, whereas the abductor muscle sheet is entirely made up of white muscle fibres.