Gut regulatory peptides in some Antarctic notothenioids

The presence and the comparative distribution of regulatory peptides and serotonin in the gut of four species of Antarctic notothenioid fishes [Cryodraco antarcticus and Chionodraco hamatus (Channichthyidae), and Trematomus bernacchii and Trematomus newnesi (Nototheniidae)], were immunohistochemically studied. In these species, numerous immunoreactive (IR) endocrine cells and nerve elements were detected. In the nototheniids most of the IR nerve fibres were of the intrinsic type, while most of the IR nerve fibres of the channichthyid intestine, besides insulin-like IR fibres, seemed to be of the extrinsic type. The intensity and frequency of immunopositivity are not the same in channnichthyids and nototheniids; the species belonging to the first family show many differences from the teleosts living in temperate water. The finding of insulin-like endocrine cells and nerve fibres in the gut wall of Cryodraco antarcticus is exceptional for vertebrates and deserves special attention.