Physiological adaptation of Antarctic teleosts to cold environment was studied with regard to the presence of regulatory peptides involved in (i) cardiac and ion-water homeostasis, (ii) brain, (iii) intestine, and (iv) gonads. Immunoreactivity for different regions of the Atrial Natriuretic Peptide was detected in the heart of Trematomus bernacchii, Chionodraco hamatus, Cryodraco antarcticus, and Champsocephalus gunnari, while immunoreactivity for other regulatory peptides (i.e., endothelin-1, somatostatin-14, and galanin) appeared to be widely distributed in the cardio-vascular system. Osmoregulatory peptides (somatostatin-14, prolactin, atrial natriuretic peptide, galanin, and urotensin II) were localised by immunohistochemistry in the urinary bladder and gills. From studies on the distribution of the pituitary specific transcription factor 1 and adenohypophysial hormones (growth hormone, prolactin, and gonadotropin releasing hormone) in the brain and pituitary of Trematomus bernacchii and Pagothenia coriiceps, it was evident that the pituitary specific transcription factor 1 acts as a developmental regulator of the anterior pituitary, responsible for growth hormone and prolactin cell commitment, differentiation, and gene expression. This coexistence appeared to be a unique trait of Antarctic teleosts. Analyses of the distribution and localisation of gastrointestinal hormones and neuropeptides (insulin, glucagon, pancreatic polypeptide, somatostatin, vasoactive intestinal polypeptide, pituitary adenylate cyclase activating peptide, and peptide histidine isoleucine) in adults of Chionodraco hamatus, Pagetopsis mascropterus, and Notothenia coriiceps, and larvae of Pleuragramma antarcticum showed that most of the immunoreactive nerve fibres in Notothenioids are of extrinsic type. Ultrastructural analysis of Chionodraco hamatus, Champsocephalus gunnari, and Notothenia coriiceps male gametes showed some peculiar aspects in the head of the spermatozoa. Studies on the spermatogenesis indicated a shifted circannual cycle in the icefishes and in the red blooded fishes: when spermatogenensis is completed in the icefish, in the red blooded teleosts the testis is not in reproductive activity as shown by the positive immunoreaction for Fibroblast Growth Factor and its receptor 1 in spermatogonia and Sertoli cells of Chionodraco hamatus and the lack of positivity in Trematomus bernacchii.
