Oxygen availability causes morphological changes and a different VEGF/FIk‐1/HIF‐2 expression pattern in sea bass gills

Abstract

The sea bass, Dicentrarchus labrax, is abundantly reared in intensive aquaculture and oxygen is one of the most important parameters. The gills of D. labrax exposed for three months to three different oxygen partial pressure conditions were investigated: normoxia, mild hyperoxia and mild hypoxia (respectively, 90–100%, 120–130% and 60–70% of the saturation value). Modifications to Po2 levels were studied with morphological and immuno‐histochemical techniques. In normoxia and mild hyperoxia conditions, the gills had the typical structure with rows of parallel filaments; nevertheless, hyperoxia treatment altered the pillar cell structure, leading to an enlargement of the vascular lumen. In hypoxia condition, gills were disorganized, the vascular lumen was reduced and the lamellae showed apical blebs and outer epithelial detachment. In vertebrates, the vascular endothelial growth factor and its main receptor Flk‐1 are two important oxygen dependent molecules whose expression can be regulated by the hypoxia inducible factor 2. In D. labrax, high expression of these factors was found in normoxia and mild hypoxia, while in mild hyperoxia they were very weak. Our data characterize the morphological changes occurring in D. labrax gills and the different expression pattern of the above‐mentioned factors after exposure to different oxygen partial pressure conditions.