Influence of environmental temperature and water oxygen concentration on gas diffusion distance in sea bass (Dicentrarchus labrax, L.)

Gas diffusion distance (GDD) of sea bass was measured in fish bred under fa rm conditions, at different dissolved oxygen concentrations (DO): normoxia condition (80-100% of the saturation value) and 'mild' hyperoxia condition (120-130% of the saturation value). Measures were carried out two times in a year (beginning of summer and autumn) in order to evaluate the effect of water temperature on GDD at the two different dissolved oxygen concentratio ns. There was a significant influence of both dissolved oxygen concentratio n (p less than or equal to0.001) and environmental temperature (p less than or equal to0.001) on GDD. In summertime it was 1.75 mum and 2.31 mum for f ish reared under normoxia and hyperoxia, respectively, and in autumn 2.51 m um and 2.96 mum for fish reared under normoxia and hyperoxia, respectively. When DO was reduced at the higher temperatures, GDD decreased as well. Res ults lead to the conclusion that GDD increased with the increasing of DO, b oth due to reduced water temperature and to the mild oxygen hypersaturation following application of pure oxygen. The advantage for fish may be found in the compromise between maximising O-2 diffusion at the gills and ions/wa ter intake/loss, known as 'osmoregulatory compromise'.