Abnormalities of a gill cover bone, the operculum, in perch Perca fluviatilis from a pulp mill effluent area

Abnormalities of a gill cover bone, the operculum, were found in perch Perca fluviatilis from an area affected by pulp mill effluents in the Gulf of Bothnia, Baltic Sea, Sweden. One of the abnormalities was expressed as a shortening of the distal part of the operculum, and was termed opercular deformity. This deformity was quantified by taking two measurements of the operculum. The second abnormality was manifested as craterous formations on the operculum. Both abnormalities were studied using a sample of opercula collected in the pulp mill effluent area between the years 1982 and 1989. The maximum prevalences of the abnormalities, 34% for the craterous formation and 20% for the opercular deformity, were found in 1983 and 1984, respectively. In a reference area the prevalences were 1% and 1.4%, respectively. After 1984, the prevalences decreased together with prevalences of other fish diseases and deformities in the same area. This coincided with a reduction in concentrations of effluent. The observed high prevalence of the opercular deformity and the craterous formations were attributed to the effects of the pulp mill effluent. In addition, an analysis of the biochemical composition opercula from perch caught in another pulp mill effluent area showed a dose-dependent alteration of several constituents, indicating a relationship with exposure to the effluent. This study shows the potential of opercular abnormalities to monitor effects of pulp mill effluents, and also, it is suggested, for retrospective studies on large samples of opercula used for age determination in ecological studies of fish.