Description and Prevalence of Ichthyophonus in Yellowtail Flounder on Georges Bank

The parasitic protozoan, Ichthyophonus sp., has been a growing concern to yellowtail flounder (Limanda ferruginea).   The yellowtail stock on Georges Bank has many implications for fisheries management, in recent years the stock estimates have been decreasing, limiting commercial fishing.  Ichthyophonus sp. has been identified as the causative agent in mass mortality for several species in Atlantic waters.   Yellowtail flounder were sampled every six weeks since June 2012 during a seasonal bycatch survey of the United States waters on Georges Bank.  After capture the peritoneal and pericardial cavity was observed macroscopically for any observable abnormalities.  Each abnormality was noted, imaged and preserved in 10% neutral buffered formalin for histological evaluation. The majority of yellowtail flounder sampled in this study hosted a variety of parasites including Ichthyophonus sp. as well as nematode and cestode parasitism.   The individual fish with clinical signs of Ichthyophonus sp. were severely infected with systematic inflammation replacing the host’s vital organs with granulomatous and necrotic cells. Histological results suggest that Ichthyophonus sp. may spread quickly through tissues causing significant damage and resulting in mortality.  During this study yellowtail flounder had a prevalence of 2.7%, the work will continue to monitor changes and identify potential epizootic events.