Impairment of retinal function in yellow perch by metacercariae.

Histologic studies of fish from Douglas Lake, Cheboygan County, Michigan, USA show that spp. infect the lens of spottail shiners () and common shiners (). In contrast, infection was confined to the choroidal vasculature of yellow perch (), and the morphology of the pigment epithelium and retina in regions adjacent to the metacercariae was abnormal. The difference in location of metacercariae within the host suggested that different species may infect shiners and perch in Douglas Lake. Species diversity was investigated by sequencing the barcode region of the cytochrome oxidase I gene of metacercariae. Four species of were identified, all four of which were present in shiner lenses; however, only was present in the perch choroid. To determine whether infection of perch eyes affects the response of the retina to a light stimulus, electroretinograms (ERG) were recorded. The amplitude of the b-wave of the ERG was reduced and the b-wave latency was increased in infected perch, as compared to uninfected eyes, and the flicker-fusion frequency was also reduced. Infection of the yellow perch choroid by , which shows strong host and tissue specificity, has an adverse effect on retinal function, lending support to the hypothesis that parasite-induced impairment of host vision may afford the evolutionary benefit of increasing the likelihood of transmission, via host fish predation, to its definitive avian host.