Amino acid analyses and peptide mapping were performed for the four main haemoglobins from the armoured catfish Pterygoplichthys pardalis; component I, which is functionally distinct from the others, is structurally unique, whereas components II, III and IV, functionally indistinguishable, are closely related in structure. Compositional difference indices are calculated for the four components and for the two major haemoglobins from the trout Salmo irideus, and the results are discussed in terms of structural relationships and evolutionary history of fish haemoglobins.
