A New Eye Disease in Pen-Reared Chinook Salmon Caused by Metacestodes of Gilquinia squali (Trypanorhyncha)

Abstract

Eye infections by metacestodes of Gilquinia squali (Cestoda: Trypanorhyncha) were associated with mortality in chinook salmon Oncorhynchus tshawytscha reared in net-pens in seawater at two separate locations in British Columbia. Mortality associated with the disease was about 10% at one site and undetermined at the second site. The metacestode was found in the vitreous humor of moribund fish with eye lesions, whereas healthy fish from the same pen exhibited neither eye lesions nor the infection. The lesions were characterized by retinal folding and apparent retinal duplication, and cataractous changes; in severe cases, the cornea ruptured, and the lens was extruded. The spiny dogfish Squalus acanthias i s the definitive host for the cestode. Spiny dogfish were prevalent in and around the affected net-pen sites, thus providing coracidia to infect the first intermediate host, which is most likely a crustacean. Although the metacestode is common in the eyes of European whiting Merlangius merlangus in the northeast Atlantic region, this is the first report of the infection in a salmonid.