Abstract
In the present study, groups of ruffe Gymnocephalus cernuus , reared singly, were exposed to defined numbers of Anguillicoloides crassus or Camallanus lacustris under controlled laboratory conditions. Infection took place orally through feeding G. cernuus with axenically cultured and laboratory infected copepods, in which the parasites had developed to the infective third stage (L3). Mean prevalence (94·3%) and infection probability (38·5%) for the established C. lacustris were significantly higher than for the neozoic A. crassus (14·3 and 1·0%, respectively). Peripheral blood leukocytes were significantly increased in infected fish, apparently independent of exposure level, parasite species or intensity of infection compared to the controls. In infected fish, the gonado‐somatic index ( I G ) was significantly reduced by c. 50%, and the spleen‐somatic index ( I S ) was significantly increased compared to controls. Both parasites raised similar physiological and immunological responses in G. cernuus , which was able to effectively reject the neozoic A. crassus .