Microradiography of otoliths and vertebral centra in the flatfish Limanda herzensteini: Hypermineralization in the hyaline zones.

Abstract

The otolith and vertebral centrum of the flatfish Limanda herzensteini were microradiographed to find differences in mineral density between the hayline and opaque zones. In the opaque zone of the otolith, the lamellated structure was well developed and appeared as several thick bands of dark brown. The interlamellar spaces contained some material which appeared light brownish under transmitted light. In the hyaline zone, however, the thick lamellae marked by the brown bands were not noticeable and instead thin lamellae containing little brownish material in the interlamellar spaces could be discerned. The thick lamellae showed the highest X-ray permeability and next came the brownish spaces between the lamellae of the opaque zone. Although the thin lamellae were slightly radiolucent, the hyaline zone showed the lowest X-ray permeability as a whole. High radiolucency was also observed in the central area of the otolith, which had a well-developed lamellated structure. In the centrum, the hyaline and opaque zones consisted of an assembly of lower-order opaque and hyaline layers, which were predominant in the respective zones. Microradiographs showed the opaque to be more radiolucent than the hyaline layers, indicating that as a whole the hyaline zone is more compact than the opaque zone. In conclusion, the otolith and the vertebral centrum showed the identical characteristic of having a higher degree of mineralization in the hyaline zones than in the opaque zones.