Host‐parasite interactions between <i>Ichtyobodo necator</i> (Henneguy, 1883) and farmed salmonids

Abstract

Abstract. The prevalence and intensity of Ichtyobodo necator infestations on farmed salmonids was investigated over a 7‐month period. The infestations were found to be markedly age dependent. Ichtyobodo infestations peaked at 4 weeks after commencement of first feeding and mortalities peaked at 4 6% per week at 8 weeks in the 0+ fish. Both infestations and mortalities showed a marked decline to zero shortly after these periods with no chemotherapy. No Ichtyobodo were seen on the 1+ fish until late in the study after a drop in temperature to below 10°C, when they reappeared on the 0+fish also. Ichtyobodo were found at temperatures between 3–5°C and 16°C and in the 0+fish appeared irrespective of the condition of the fish. It is suggested that some form of host defence mechanism is operating which limits the Ichtyobodo infestations in farmed salmonids.