Association between growth, body condition and anti-predator behaviour in maturing and immature brown trout parr

In spring there were significant differences between maturing and immature brown trout Salmo trutta in anti-predator behaviour to pike and heron model s when all behaviours were combined in multivariate analysis. However, the time until the trout visited the patch in the experimental tray where preda tors attacked was the only variable that alone significantly differed betwe en maturity groups; following transfer between the rearing tank and the exp erimental tray, maturing fish visited this patch sooner. The difference in anti-predator behaviour coincided with differences developing between the g roups in both growth rate and condition factor, Maturing fish showed higher growth rates and exceeded immature fish in condition factor from spring on wards. In a summer experiment, no differences in anti-predator behaviour we re observed between maturing and immature fish. It is concluded that increa sed risk-taking to facilitate higher food intake is probably the behavioura l mechanism responsible for the comparatively greater increases in growth a nd body condition observed among maturing fish in spring, (C) 2001 The Fish eries Society of the British Isles.