EFFECTS OF OXYGENATION AND THE STRESS HORMONES ADRENALINE AND CORTISOL ON THE VISCOSITY OF BLOOD FROM THE TROUT ONCORHYNCHUS-MYKISS

Although the concentrations of the stress hormones adrenaline and cort isol in rainbow trout (Oncorhynchus mykiss) blood increase upon hypoxi c exposure, the combined effects of these hormones and O-2 lack upon f ish blood theology have not been investigated. Deoxygenated blood take n by caudal puncture exhibited lower viscosities than oxygenated sampl es at low shear rates, whereas the opposite was true at high shear rat es. However, blood from cannulated trout had similar viscosities in it s deoxygenated and oxygenated states. In the deoxygenated state, addit ion of adrenaline lowered viscosity at low shear rates and increased i t at high shear rates, resembling the effects of deoxygenation observe d in blood taken by venepuncture. In oxygenated blood on the contrary, no marked adrenaline effects were observed, In deoxygenated blood, ad dition of cortisol lowered viscosity at all measured shear rates compa red with blood without cortisol. In oxygenated blood, however, no cort isol effects were observed. The viscosity effects observed in the pres ence of cortisol could not be attributed to concomitant changes in hae matological variables. However, the effects in the presence of adrenal ine manifested in deoxygenated 'cannula' blood and in uncannulated blo od without added hormones appear to result from parallel increases in haematocrit and cell volume.