ABSTRACT
From the comparative point of view fish endocrine organs, and the hormones they secrete are much more interesting to zoologists than are those of terrestrial vertebrates (Bern, 1985, 1990). It will not come as too much of a surprise to guess that various groups of fishes show different stages in the evolution of the endocrine systems found in other vertebrates. Possibly it may be less evident that these have led to new ideas about the possible ligand and receptor changes leading to those of terrestrial vertebrates, and they have supported genome duplication theories in vertebrate ancestry, first suggested by Ohno (1970) and by studies on Hox genes (see p. 11). Thus, for instance, Conlon and Larhammar (2005) discuss the evolution of the neuropeptide Y and tachykinin neuroendocrine families in relation to genome duplications.
