Water oxygenation and osmo-respiratory compromise in Sea bass (Dicentrarchus labrax, L.)

The effects of dissolved oxygen (PO2) on gills Gas Diffusion Distance (GDD) and Respiratory Surfacie Area (RSA) has been previously reported by Saroglia et al. (2000) and by Saroglia et al., 2002. The increase if GDD and a reduction of RSA have been described as consequences of an higher PO2 availability. The basic conflict between gas exchange and ion regulation in the gills of freshwater fishes is described by Randall et al. (1972). They indicated that a large permeable gill membrane is required for an efficient gas transfer, but a small, impermeable epithelium is needed to minimize diffusive ion losses. The authors also demonstrated that rainbow trout accelerate Na+ losses with an increase in oxygen consumption during exercise, which they attributed mainly to an increased Functional Surface Area (FSA) of the gills during activity. As suggested by Nilsson (1986), the balance between ‘need of oxygen’ and ‘need of osmotic regulation’ was defined as ‘osmo-respiratory compromise’..