Anaemia is a common pathology associated with many infectious and non-infectious diseases. The effects of haemolytic anaemia induced by i.p. injection of phenylhydrazine (PHZ) were studied in Atlantic cod. Phenylhydrazine injection (0.3 mg kg(-1)) in a DMSO and saline vehicle induced a reproducible and stable anaemia reducing haematocrit, (Hct) by 62% over 3 weeks. Controls consisted of fish injected with saline and DMSO/saline vehicle with minimal effects on Hct or whole blood haemoglobin (Hb). Although anaemia resulted in reduced blood lactate and glucose in PHZ injected fish, there were no effects of anaemia on blood, sodium, chloride or potassium. Similarly, there were no changes in the relative proportions of leucocytes in the blood although an increase in the number of immature erythrocytes was observed in the anaemic fish. Anaemic fish showed a 29 and 22% increase in cardiac somatic index (CSI) relative to saline and vehicle controls, respectively, although there were no significant differences in the linear dimensions of the ventricle. Changes in cardiac somatic and ventricular somatic index correlated positively and significantly with Hct but not with whole blood Hb concentration. Anaemic fish had significantly reduced resting routine oxygen consumption compared with vehicle controls but were not able to increase oxygen consumption following a bout of exhaustive exercise. Plasma lactate concentrations increased significantly after exercise to a greater extent in anaemic fish compared with vehicle control fish. Phenylhydrazine is a useful model for studying haemolytic anaemia in Atlantic cod with minimal effects on blood biochemistry and haematology and clearly reduces the aerobic capacity in Atlantic cod.

Phenylhydrazine injections (0.3 mg kg(-1) , followed by a second injection of 0.1 mg kg(-1) 7 days later) induced a reproducible and stable anaemia in Atlantic halibut Hippoglossus hippoglossus, reducing the haematocrit and haemoglobin by 70.0 and 75.5%, respectively, over 3 weeks. There were no changes in blood electrolyte or lactate concentrations, although anaemic fish showed a 37.5 and 33.0% increase in cardiac somatic index and ventricular somatic index, respectively, compared with dimethyl sulphur oxide (DMSO) and saline vehicle controls. Changes in cardiac somatic indices did not correlate with the ratio of ventricular length:height and length:width did correlate with haematocrit and haemoglobin indicating that changes in cardiac shape may occur as a function of anaemic hypoxemia.