The effect of rearing conditions on development of saddleback syndrome andcaudal fin deformities in Dentex dentex (L.)

The development of saddleback syndrome and of caudal fin deformities in Den tex dentex (Linnaeus, 1758) was compared under two rearing methods, extensi ve (E) and semi-extensive (S). The osteological appearance and the meristic characters of the reared fish were compared to that of D. dentex juveniles , collected from the natural environment. All the wild juveniles were norma l in respect to their osteological appearance, while the reared specimens p resented skeletal deformities resulting from different rearing methods appl ied. Saddleback syndrome (4.0-4.4%) and severe external deformities of the caudal fin (14.3-15.0%) characterised exclusively the semi-extensive popula tions, while the extensive populations presented severe abnormalities of th e pre-ural centra (25.0-25.6%) with significantly higher frequency than the S reared fish (5.8%). Saddleback syndrome was expressed as a lack of one t o all the hard spines of the dorsal fin, accompanied by shape, number and p osition abnormalities of the related pterygiophores. Caudal fin deformities were mainly characterised by the lack of the upper lepidotrichia or/and de rmatotrichia, accompanied by severe deformities of the supporting elements of the upper lobe. The saddleback syndrome and severe caudal fin deformitie s were anatomically and ontogenetically related to each other, originating at the early larval stage as a result of abnormalities of the primordial ma rginal finfold and of the posterior tip of the notochord. In respect to the dominant phenotypes, the meristic characters of the normal reared fish wer e not differentiated from those of the wild, but they presented higher vari ability. The results are discussed in view of the aetiology, applications and resear ch targets for the erasure of skeletal malformations. (C) 2001 Elsevier Sci ence BN. All rights reserved.