Baseline studies of biomarkers in the feral female perch (Perca fluviatilis) as tools in biological monitoring of anthropogenic substances

Since 1988, yearly measurements of several physiological and biochemical variables have been performed using feral female perch (Perca fluviatilis) from an assumed reference area in the Baltic proper, Kvädöfjärden. The area is divided into two stations, Meta and Häxvassen, approximately 20 km apart. Standardized sampling and measurements have shown that a number of variables such as somatic body weight, total length, gonadosomatic index, liversomatic index, condition factor, hematocrit, lactate in blood and chloride ions in the blood plasma are generally stable from station to station and from year to year. The percentage of different leucocytes showed a comparatively large variation from one year to the next. Ethoxyresorufin-O-deethylase has shown an increase in activity over recent years indicating an increased exposure to pollutants.