THE LIFE‐HISTORY OF THE BULLHEAD OR MILLER'S THUMB (COTTUS GOBIO L.)

Abstract

SUMMARY 1,555 Bullheads (Cottus gobio L.) from Windermere, 771 from the river Brathay and 542 from other waters, 2,868 in all, were caught between January 1951 and December 1955. The fish lives on the margins of lakes and in rivers under stones where there is a sandy or gravelly bottom. Differences in behaviour of breeding and non‐breeding fish are described. Males mature earlier in the year than females and large females lay eggs earlier in the breeding season than small ones. In the river Brathay, most fish do not breed before they are two years old, but in Windermere fast‐growing fish breed when one year old. Fish from Windermere have a greater fecundity than those from the river Brathay. Age was found from otoliths. Male fish grow faster than females in both the river Bray and Windermere and fishes of both sexes grow faster in the lake than they do in the river. The food, which is mainly invertebrate bottom fauna, varies more with season and place than with size of fish or year of capture. In both Windermere and the river Brathay the fish feeds mostly on nymphs of Ephemeroptera and Plecoptera and larvae of Trichoptera, but in Windermere, unlike the river Brathay, Gammarus and Sialis are also commonly eaten. The fish has many parasites, of which only one in the urinary bladder (Phyllodistomum folium) has been identified, and apparently no serious predators.