Eye fluke infection status in Baltic cod, Gadus morhua, after three decades and their use as ecological indicators.

Eye flukes of the genus Diplostomum were recorded with a prevalence of 7.4% and a mean intensity of 11.9 (range 1-75) parasites per fish in eye lenses of a total of 188 Atlantic cod, Gadus morhua, sampled in the Southeastern Baltic Sea from March 2013 to February 2014. A slight decrease of infection level, among the fish with body length ranging from 30 to 89.5 cm, was found when data were compared to a corresponding survey in the 1980s. Due to imprecise species identification of eye flukes based on morphometric analyses we present, as a baseline for further studies, rDNA sequences from a subsample of 19 eye flukes based on sequencing of a part of 18S, ITS-1, 5.8S, ITS-2 and part of 28S. We discuss the use of eye fluke recordings in Baltic cod as an environmental indicator due to the dependence of the parasite´s life cycle on biotic (occurrence of snail and bird hosts) and abiotic (temperature and salinity) parameters. [ABSTRACT FROM AUTHOR]