Parasite host relations: Hexamita salmonis in rainbow trout Oncorhynchus mykiss

The relationship between host size and infection, the site selection in the host and the association between health status and infection were studied in Hexamita salmonis (Moore, 1923) infected rainbow trout from commercial trout farms. During a 1 yr survey it was shown that the flagellates occur primarily In the smallest fry. The site occupied by the parasite is preferentially the pyloric region and the anterior intestine but in heavily infected fish the parasites occur throughout the entire length of the gut. Infected fish exhibited significant anorexia and significant body weight reduction.