Tissue damage and parasite frequency in flounders, Platichtys flesus (L.) chronically exposed to bleached kraft pulp mill effluents

One-year-old flounders, Platichtys flesus (L), were exposed to kraft pulp mill effluent during a two-month period in an artificial ecosystem corresponding to the littoral zone of the Baltic Sea. The fish were exposed to 1 or 2.5 % concentrations (v/v) of different types of total effluents from mills producing bleached and unbleached pulp, respectively. Fish caught in the vicinity of the discharge pipe of a pulp mill were used as reference field material. Structural differences in gill and liver tissue were detected in the exposed fish. These seemed to be positively correlated with the chlorine bleaching in the process of pulp production. The reference fish were most heavily infested with a tricodinid ciliate, followed by the fish exposed to effluents from mills using oxygen and chlorine in the bleaching process.