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

Abstract

In spring there were significant differences between maturing and immature brown trout Salmo trutta in anti‐predator behaviour to pike and heron models when all behaviours were combined in multivariate analysis. However, the time until the trout visited the patch in the experimental tray where predators attacked was the only variable that alone significantly differed between maturity groups; following transfer between the rearing tank and the experimental tray, maturing fish visited this patch sooner. The difference in anti‐predator behaviour coincided with differences developing between the groups in both growth rate and condition factor. Maturing fish showed higher growth rates and exceeded immature fish in condition factor from spring onwards. In a summer experiment, no differences in anti‐predator behaviour were observed between maturing and immature fish. It is concluded that increased risk‐taking to facilitate higher food intake is probably the behavioural mechanism responsible for the comparatively greater increases in growth and body condition observed among maturing fish in spring.