Delayed spawning of perch, <i>Perca fluviatilis</i> L., in acidified lakes

Abstract

The timing of spawning of perch was examined in four acidified lakes (pH 4.4–4.8) and in one circum‐neutral lake (pH 6.3) in southern Finland in spring 1987. In three of the lakes, perch started to spawn soon after the ice melt (4–14 degree days &gt; 5° C) and had spawned by the end of May at about 100 degree days &gt; 5° C. In the two most acidified lakes, fish started to spawn later, at 35 and 60 degree days &gt; 5° C, and had spawned in early June, at about 200 degree days &gt; 5° C. The maturing of gonad products was delayed in both males and females.