Blood oxygen transport, rheology and haematological responses to confinement stress in diploid and triploid Atlantic salmon, Salmo salar

Ž . Diploid and triploid all-female Atlantic salmon Salmo salar smolts were challenged with 2.5 h of confinement stress in aerated seawater. Subsequent stress responses were quantified by Ž . plasma cortisol, glucose, and lactate, and by the haematological parameters haematocrit Hct , red Ž . Ž . Ž . blood cell count RBCC , mean cell volume MCV , blood haemoglobin concentration Hb , mean Ž . Ž . cell haemoglobin MCH , mean cell haemoglobin concentration MCHC , total protein and Ž . erythrocyte adenosine triphosphate ATP . The magnitude of stress responses was similar between diploid and triploid smolts. Triploid smolts displayed a higher MCH, but lower Hb than diploid smolts. The blood oxygen affinity of diploid and triploid fish was similar at 158C over the pH range 6.76–7.99 and the isohaemoglobin components were identical. The enlarged triploid erythrocytes showed reduced shear-dependence on blood viscosity at constant Hct and are therefore unlikely to contribute to greater peripheral vascular resistance. The results show that despite having fewer, larger erythrocytes, triploids have very similar oxygen carrying capacity and haematological response to stress as diploids. This suggests that the higher farm mortality reported for triploids in response to stress is not generated by their failure to show respiratory homeostasis in the face of stress. q 2000 Elsevier Science B.V. All rights reserved.