Presence of paraneuronal pseudobranchial neurosecretory system in the gill region of two air-breathing clupeids, Notopterus chitala and Notopterus notopterus

The pseudobranchial neurosecretory system (PNS) is a system of neurosecretion observed in certain groups of teleosts, which are air-breathing or known to tolerate low oxygen tension in the surrounding water. Like other neuroendocrine cells of gill, cells belonging to this system have also been observed to have a role in condition of hypoxia. Uniformly found in all catfish species, the system was reported to be present in few non-catfish groups also, viz.-Atheriniformes, Channiformes (Devi, 1987), Perciformes, and Clupeiformes (Srivastava et al., 1981; Gopesh, 1983). In an attempt to study the structure and organization of the pseudobranchial neurosecretory system in non-catfish species of teleost, present investigation was undertaken in two species of Notopterus, viz. Notopterus chitala and Notopterus notopterus. The histological observations, using neurosecretion specific stains, undertaken on two clupeids are reported and the findings are discussed in the light of association of PNS with Carotid gland-a structure of intermediate stage in the process of transformation of pseudobranch into the carotid labyrinth, in course of evolution and also the air-breathing habit of the fish.