BULLETIN OF THE EUROPEAN ASSOCIATION OF FISH PATHOLOGISTS
The high incidence of opercular deformities appearing in Mediterranean marine hatcheries is an important problem which is causing considerable economic losses. The aetiology of this syndrome is not yet well understood. In this study a histological and ultrastructural description of gilthead sea bream larvae (Sparus aurata) affected with anomalies of the opercular complex was 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 processes were found in the opercular tissues. The electron microscopy observations 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 connective tissue formation and an abnormal mineralisation of the fibrous bone can predispose opercular folding.