Dissolved oxygen regimen (P O ₂) may affect osmo respiratory compromise in Eur

摘要

Fundamentally, in land based mediterranean aquaculture, two techniques are applied to supply water with oxygen: paddling water aeration and application of pure oxygen. The two oxygenation techniques result in quite different PO₂ regimens and, consequently, different fish growth performance and gill morphology. Data exist showing a reduction in total respiratory surface (RSA) and increasing gas diffusion distance (GDD) in gills of sea bass (Dicentrarchus labrax, L.) farmed under elevated PO₂ regimens. That such a modification might have an effect on the ion regulation has been defined elsewhere as osmorespiratory compromise. In this study, European sea bass previously acclimatized to two PO₂ regimens, mild hypoxia and mild hyperoxia (70–80% and 130–140% of the saturation value, respectively), were challenged for 1 hour with hypo-osmotic plus manipulation stress in two separate trials. During the first trial, when only Na+ loss was determined, the ion efflux during the first 5 min resulted in a rate of 163.72±31 and 112.23±87 nmol g?1 min?1 from hypoxia and hyperoxia sea bass groups, respectively, and, if sustained, would approach 15.3 and 11.2% per hour of the total body Na+, respectively. During the second trial, in which both Na+ and Cl? loss were determined, after 60 min the Na+ loss was shown to be 76.86±12 and 179.28±32 nmol g?1 min?1 for the fish previously acclimatized to hyperoxia and hypoxia regimens, respectively, whereas for Cl? this loss was 62.02±11 and 157.28±28 nmol g?1 min?1, respectively. Our data are compatible with the hypothesis of an osmotic advantage of sea bass exposed to an elevated PO₂ regimen, achievable with application of pure oxygen, instead of simple water aeration.