ABSTRACT
Although the concentrations of the stress hormones adrenaline and cortisol in rainbow trout (Oncorhynchus mykiss) blood increase upon hypoxic exposure, the combined effects of these hormones and O2 lack upon fish blood rheology have not been investigated. Deoxygenated blood taken by caudal puncture exhibited lower viscosities than oxygenated samples at low shear rates, whereas the opposite was true at high shear rates. However, blood from cannulated trout had similar viscosities in its deoxygenated and oxygenated states. In the deoxygenated state, addition of adrenaline lowered viscosity at low shear rates and increased it at high shear rates, resembling the effects of deoxygenation observed in blood taken by venepuncture. In oxygenated blood on the contrary, no marked adrenaline effects were observed. In deoxygenated blood, addition of cortisol lowered viscosity at all measured shear rates compared with blood without cortisol. In oxygenated blood, however, no cortisol effects were observed. The viscosity effects observed in the presence of cortisol could not be attributed to concomitant changes in haematological variables, However, the effects in the presence of adrenaline manifested in deoxygenated ‘cannula’ blood and in uncannulated blood without added hormones appear to result from parallel increases in haematocrit and cell volume.
