Données nouvelles sur la structure et la minéralisation des écailles d'Anguilla anguilla (Osteichthyes, Anguillidae)

The structure of the scales in Anguilla anguilla was studied by light and electron microscopy and the mineral phase was analyzed by histophysical techniques. Although the scales of the eel are small in size and have a peculiar superficial ornamentation, which consists of a web of mineralized plates, they are composed of the three characteristic layers of the typical elasmoid scale. The discontinuous, superficial outer limiting layer is highly mineralized; in this layer, acid mucosubstances are abundant but collagen fibres are absent. Mineralization in the external layer is not oriented by the network of the thin collagen fibrils. In the basal plate, mineralization is oriented by the thick collagen fibres packed in bundles. The bundles are oriented from the basal part to the surface of the scale but they are not organized in the laminated structure characteristic of most other teleost scales. The mineral phase of the eel is typical of a teleost fish. The peculiar features of the scale in the eel are interpreted here as a discrete example of the phyletical reduction of the dermal skeleton among Actinopterygii.