Diel rhythm of emergence and of first displacement downstream in trout (Salmo trutta), Atlantic salmon (S. salar) and grayling (Thymallus thymallus)

The diel rhythm of emergence from the gravel and displacement downstream has been studied in three salmonoid species: brown trout (Salmo trutta L.), Atlantic salmon (S. saiar L.) and grayling (Thymallus thymallus L.). Grayling emerged in the morning but delayed downstream displacement until the night, while the Salmo species emerged just before downstream displacement chiefly at night.