Histological and ultrastructural study of opercular anomalies in gilthead sea bream larvae (Sparus aurata)

The high incidence of opercular deformities appearing in Mediterranean mari ne hatcheries is an important problem which is causing considerable economi c losses. The aetiology of this syndrome is not yet well understood. In thi s study a histological and ultrastructural description of gilthead sea brea m larvae (Sparus aurata) affected with anomalies of the opercular complex w as carried out. The first opercular alterations were detected 17 days after hatching, when the opercular support in the branchio-cranial area was still cartilaginous and the only structure of the opercle is a connective laminae composed of a dense connective tissue. No degenerative alterations or inflammatory proce sses were found in the opercular tissues. The electron microscopy observati ons on 30 days-old larvae allowed the identification of abnormality in the mineral deposition within the dermal ossification in curled opercles. These preliminary observations suggest that an early alteration in the connectiv e tissue formation and an abnormal mineralisation of the fibrous bone can p redispose opercular folding.