The stress‐response of rainbow trout to experimental infection with the blood parasite Cryptobia salmositica Katz, 1951

Abstract

Physiological responses of rainbow trout, Salmo gairdneri Richardson, to experimental infection with the blood haemoflagellate Cryptobia salmositica were monitored for 7 weeks to determine whether the parasitaemia elicited a classical stress‐response as evidenced by elevated plasma cortisol and glucose levels. There was a progressive anaemia, hepatomegaly, splenomegaly, and depressed plasma T3, T4, protein and glucose concentration, and lowered liver glycogen content in the parasitized fish throughout the study, which clearly indicated that the animals were under physiological duress. Moreover, these hormonal and metabolic indicators showed no indication of recovery with the decline in blood parasite numbers. However, there were no differences in plasma cortisol or glucose levels between infected and control fish throughout the study, suggesting that the parasitaemia did not activate the pituitary‐interrenal axis.