Growth and migration of plerocercoids of Triaenophorus crassus Forel and pathology in experimentally infected whitefish, Coregonus clupeaformis (Mitchill)

Abstract

The development, movement, and migration of the plerocercoid of Triaenophorus crassus in experimentally infected whitefish fry, Coregonus clupeaformis, were examined and the pathology of infection described. Plerocercoids penetrated through the stomach – pyloric caeca and anterior small intestine into the peritoneal cavity by 20 h postinfection (PI). Worms entered the muscle by day 5 PI and underwent a variety of migration patterns. Plerocercoid movement in muscle was aided by a series of peristaltic waves along the length of the worm. Plerocercoids underwent rapid growth during the first 2 months of infection and were wound extensively through the muscle by day 60 PI, at which time they occasionally penetrated into the peritoneal cavity or through the host integument. Migration of worms caused muscle necrosis resulting in formation of lesions by day 17 PI and granulomas by day 60 PI. Coincident with coiling of plerocercoids after day 60 PI was the formation of a host capsule around the worm and the initiation of plerocercoid hook development. Capsules and coiling of plerocercoids caused regional distortions in the body of the fish and displaced and (or) replaced large areas of muscle. Capsules containing live worms were recovered at 3 years PI. Mortality of infected whitefish was 21.7%, and 70.0% of this mortality occurred between days 48 and 59 PI. There was no difference in the rate of growth and the quantity of liver glycogen between infected and uninfected fish.