Abstract
To assess the correlation between four visual morphological types based on body colour and shape (fario trout, FT ; shiny fario, SFT ; presmolt trout, PST; typical smolt ST) of juvenile brown trout Salmo trutta during downstream spring migration and the biological form at the adult stage (river or sea), mark–recapture experiments were carried out over a period of 23 years. Evidence is provided that the visual SFT type is not a relevant one, while objective colorimetric measurements using a black basin are the best way to determine the morphological type in migrating juveniles.