Structure and ultrastructure of intra-vitam parasitic destruction of the external dental tissue in the fish, Anarhichas lupus L.

Abstract Three specimens of Anarhichas lupus L. with teeth presenting burrowing lesions were studied with light microscopy, SEM, and high resolution TEM. Findings suggested that the lesions were due to fungoid invasion by Mycelites ossifragus . The burrowing lesions always originated in the more highly mineralized external tooth layer, thus distinguishing them from post-mortem soil changes which may start in any part of the tooth. The channels produced by the lesion had no particular orientation to the dentinal vascular canals. It is suggested that enzymes are secreted locally by the causal organism; burrows were thus not found at a distance from the fungus whose numerous microvilli were in close contact with the mineralized walls of the channels; this distinguishes the lesion from dental caries. Needle-shaped crystals are found within the cytoplasm or adherent to the plasma membrane of the burrowing organism. Other crystals in the immediate neighbourhood of the organism were hollow, and thus suggestive of an organism feeding on mineral material. Bacterial invasion was sometimes in association with the burrowing activity, and may play a part in it, but often appeared to be a later invasion.