Restoring Endangered Fish In Stressed Habitants. ReFISH project 1988 - 1991

Abstract

Five brown trout strains have been stocked yearly into 13 acidic (pH 4.5-5.2, 60-180 µg Al/l and 0.2-1.0 mg Ca/L) lakes in southern Norway. The lakes have been test-fished yearly. The catches show good survival in 8 lakes, with fish growing to 25-30 cm at the age of 3+. The K-factor was high and the gonadal development normal. No single chemical factor can explain the occurrence or absence of fish in the lakes. The ability to support fish seems to be lake specific, and determined by pH, calcium and/or aluminium. The use of local "acid tolerant" strains is proposed as a supplement to other acid warer mitigating techniques.