Descripteurs morphologiques de la zonation de la colonne vertébrale chez la truite arc-en-ciel Oncorhynchus mykiss (Walbaum, 1792) (Teleostei, Salmoniforme)

The biometrical study of length, height and width of the successive vertebrae constituting the vertebral axis of the rainbow trout (Oncorhynchus mykiss) allows characteristic-looking vertebral profiles to be drawn. This study shows that the classical anatomical division of the vertebral column into two regions (truncal and caudal) is morphologically unrealistic; it is better represented by a zonation in three parts: a postcephalic region (or antero-truncal region) composed of 8 to 10 vertebrae the first two of which make a peculiar “couple”; a middle region integrating the following truncal vertebrae and the 18 to 20 first caudal ones; and finally a ural region (or postero-caudal region). This morphological zonation of the rachis is probably the functional result of the major role played by the vertebrae in transmitting the propulsive forces of the trunco-caudal muscles to the snout tip during the subcarangiform swimming in the rainbow trout.