Prevalence and description of Ichthyophonus sp. in yellowtail flounder (Limanda ferruginea) from a seasonal survey on Georges Bank

Ichthyophonus sp. is a ubiquitous parasite infecting numerous fish species. Ichthyophonus sp. infection of yellowtail flounder (Limanda ferruginea) was first identified in Canadian waters in 1968. Between 2012 and 2014, fifteen seasonal survey cruises by Coonamessett Farm Foundation, randomly sampled a total of 1325 fish for at-sea examination at fixed stations on the U.S. Georges Bank sea scallop fishing grounds. A subsample of yellowtail flounders were examined internally on board the ship and animals with visible lesions were collected, processed, and examined histologically. Infected fish were concentrated in eastern Georges Bank with only two of the 32 infections collected from western Georges Bank. Both macroscopic and histological evaluation of tissues showed that 81.3% of the animals infected with Ichthyophonus sp. were severely infected.