Morphology and structure of the scales in the Gadiformes (Actinopterygii :Teleostei : Paracanthopterygii) and a comparison to the elasmoid scales ofother Teleostei

Despite the commercial importance of the Gadiformes, many aspects of their classification are weakly established and disagreements exist on the phylog enetic relationships of various families. An attempt to determine the syste matic significance of the scales is made in studying the morphology and the structure of the scales of 17 species belonging to nine families which wer e examined using light and electron microscopy. The scales are elasmoid and of the cycloid type in all families except in the Macrouridae in which the y are of ctenoid or spinoid type. All these scales show the characteristics of typical Teleostei: they are made of acellular mineralized tissues, and the plywood-like structure of the basal plate is orthogonal or at least int ermediate in Melanonus zugmayeri and Raniceps raninus. The reduction of the basal plate to only one ply in the scales of Muraenolepis orangiensis is c oncomitant with the reduced size of the scale. Collagen "TC" fibers crossin g the plywood-like structure were only found in the basal plate of the scal es of Lota Iota, the only species completely confined to freshwater. A prel iminary phylogenetic analysis suggests that Lota Iota should be excluded fr om the Gadidae. The superficial ornamentations of the scales are thought to be related to the swimming. The morphological and structural characteristi cs of the gadiform scales could be considered at least as family-dependent.