Local inflammation of the heart was found in about 20 %of both perch Perca fluviatilis and roach Rutilus rutilus from 4 lakes in central Finland during [1989][1990]. The lakes differ in their trophic state and pollution level. Epicarditis was found more often than myocarditis (22 % i n perch and 18.4 % in roach vs 16.1 and 5.4 %, respectively). Most cases of epicarditis found in perch were chronic (86 %), but only a minority of those in roach were so (24 "h), the others being acute, subacute or

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... subchronic. Myocarditis was nearly always chronic in both species No relationship was found between the stage or degree of inflammation in the fish and the pollution level in the lake, and all stages of inflammation were found at all seasons with no significant seasonal trend in their prevalence, nor was any relationship found between the prevalence of inflammation and the size of the fish in any ol the lakes. h4yocarditis and epicarditis occurred independently of each other In roach, but their joint occurrence in individual fish differed significantly from the random in perch, showi.ng a positive correlation. Macrophage centres were found in 16 % of the epicardlum specimens and 24 % of the myocardium specimens from perch and in 8.7 and 7.8 %from roach, respect~vely, as well as in the bulbus arteriosus and atrium of both species. No causative agent, such a s parasites or bacteria, was ever seen to be associated with either the inflammation or the macrophage centres. The reason for the inflammation is discussed.