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

Abstract The development of saddleback syndrome and of caudal fin deformities in Dentex dentex (Linnaeus, 1758) was compared under two rearing methods, extensive (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 normal in respect to their osteological appearance, while the reared specimens presented skeletal deformities resulting from different rearing methods applied. Saddleback syndrome (4.0–4.4%) and severe external deformities of the caudal fin (14.3–15.0%) characterised exclusively the semi-extensive populations, while the extensive populations presented severe abnormalities of the 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 to all the hard spines of the dorsal fin, accompanied by shape, number and position abnormalities of the related pterygiophores. Caudal fin deformities were mainly characterised by the lack of the upper lepidotrichia or/and dermatotrichia, accompanied by severe deformities of the supporting elements of the upper lobe. The saddleback syndrome and severe caudal fin deformities were anatomically and ontogenetically related to each other, originating at the early larval stage as a result of abnormalities of the primordial marginal finfold and of the posterior tip of the notochord. In respect to the dominant phenotypes, the meristic characters of the normal reared fish were not differentiated from those of the wild, but they presented higher variability. The results are discussed in view of the aetiology, applications and research targets for the erasure of skeletal malformations.