Effects of crowding on the behaviour of juvenile hatchery and wild landlocked Atlantic salmon ( Salmo salar L.)

Abstract

In aquaria, wild juvenile Atlantic salmon ( Salmo salar L.) were most aggressive at low population densities and hatchery salmon at intermediate or high densities, indicating differences in social development of fish reared in streams where population densities are regulated by territorial dispersion and in hatcheries where fish are confined at abnormally high densities. Social interaction interfered with feeding, resulting in hatchery salmon consuming less food than wild salmon as density was increased. Both hatchery and wild salmon became more aggressive, consumed more food, were more stationary, and exhibited less escape swimming with time. Caution should be exercised when making inferences about norms of behaviour characteristics of the species in general when either hatchery or wild fish are used as experimental subjects.