Perch (Perca fluviatilis L.) parasites reflect ecosystem conditions: a comparison of a natural lake and two acidic reservoirs in Finland

Parasite communities of perch were studied in a natural lake (Vetamajarvi) and two reservoirs (the Kyrkosjarvi and Liikapuro reservoirs) located in We stern Finland. All water bodies studied are small, shallow and humic. Howev er, the reservoirs are more acidic than the lake (pH 5.9 and 5.3 vs. 6.4). Altogether, 18 parasite species were found, but the component communities w ere reduced in the harsh conditions of the reservoirs (12 and six species) as compared with the lake (17 species). In addition, the mean number of met azoan parasite specimens per fish was markedly lower in the reservoirs (64. 3 and 14.3 specimens) than in the lake (116.1 specimens). Our prediction on the depauperation of parasite communities in reservoirs as compared with t he lake was confirmed. Many ectoparasite groups were rare and most of the d igenean parasites using molluscs as their intermediate host were absent fro m the reservoirs due to the inability of molluscs to tolerate the acidic wa ter. The only digenean parasite found in the less acidic reservoir was Buno dera luciopercae. There were also species that preferred reservoirs as was expected. The protozoan ciliate Capriniana piscium benefiting acidic water and Acanthocephalus lucii, due to the abundance of its intermediate host, w ere most prevalent in the reservoir conditions. (C) 2000 Australian Society for Parasitology Inc. Published by Elsevier Science Ltd. All rights reserv ed.