Perinotochordal connective sheet of gilthead sea bream larvae (Sparus aurata, L.) affected by axial malformations: An histochemical and immunocytochemical study

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Abstract
Background: Spinal malformations in adult teleosts occur under natural conditions and, more frequently, in culture exploitations. Skeletal deformities are linked with dysfunctions in collagen metabolism. We studied axial deviations appearing in early larval stages of cultured sea bream (Sparus aurata, L.).Methods: To evaluate connective tissue components of normal and lordotic fish we used histochemistry (alcian blue, picrosirius‐polarization, clorhydric orcein, fuchsin resorcin), immunohistochemistry (anti‐collagen I, II, III, and IV), and specific enzymatic digestions. The results were evaluated by semiquantitative methods.Results: Lordosis appeared before a vertebral column was developed, thus affecting the only skeletal structure present in the animal body, the notochord. At this stage the animal depends on the vitelline sac and an inflated swim‐bladder is missing. The region of the curvature showed strong alterations in the arrangement of the muscle bundles and irregularities in notochord and perinotochordal collagen sheet. Histochemical and immunocytochemical analysis of the periotochordal sheet revealed the presence of type II collagen, non‐sulfated glycosaminoglycans, and elastic fibers in normal and lordotic specimens. Low collagen‐proteoglycan interactions occurred in lordotic animals.Conclusions: Lordosis in Sparus aurata originated during embryonic development and was characterized by disorganized connective tissue and muscle bundles. No major differences in connective tissue constituents were seen with respect to normal specimens.