Hypoxia is like an ethiological factor in vertebral column deformity of salmon ( Salmo salar)

Abstract

In Chilean salmonicultures, vertebral column deformity (VCD) is a common pathology that lowers the quality and commercialization of the product. Hypoxia has been related to other musculoskeletal deformities in fishes, but not to VCD. The notochord has a structural and functional role in vertebral morphogenesis and in mature fish resulting in mechanical support in swimming motility. This work analyzes the morphology of the vertebral column and notochord of Salmo salar alevins starting free life (950 Accumulated Temperature Units, ATU) cultured under hypoxia (60% O 2 saturation in the water tanks) for different time periods after hatching (2, 4, 6 and 8 days). These are compared with their normoxic control (100% O 2 saturation). Using histological, histochemical and morphometric techniques, it was found that there is an association between VCD and the time of exposure to hypoxia (Pearson X 2 (5) = 60.1050 Pr = 0.0001). The time of exposure to hypoxia is inversely proportional to the body length, mineralization to the vertebral body, notochord diameter and thickness of its sheath. Hypoxia decreases collagen type II in the notochord sheath and up regulation of collagen type I. The organic response to hypoxia was quantified by immunohistochemistry for HIF-1α as the sensor of hypoxia. Its expression increased significantly (p < 0.05) in the experimental groups that exhibit VCD. Although ethiology for VCD is probably multifactorial, this study allows to conclude that hypoxia by itself, produces VCD.