Conservation status in Portugal: Critically Endangered (CR).
Like the Atlantic salmon, it is a benthopelagic species distributed in the north Atlantic, and it occurs in national territory mostly in the rivers Minho and Lima, but also in Cávado, Douro, Vouga and Mondego. It is easily mistaken with its congener Salmo salar, its superior maxilla being a distinctive factor, as it is more prolonged and can extend past the posterior edge of the eye. It also displays an adipose fin with a red margin. This species can present two distinctive forms: (i) Holobiotic – spends its entire life cycle in freshwaters and can be distinguished from amphibiotic form by its brownish colour with light reddish-centred patches; and (ii) Amphibiotic – anadromous migrator, it also undergoes a smotification process, adapting to life on the ocean, where it reaches its adults phase and sexual maturity, upon which it returns river basins to spawn. Can be distinguished from holobiotic form by its silver colour and dark patches.
Like the salmon, its effective population is estimated to be too low to be considered a viable resource for commercial exploration. Both species are significantly produced in aquaculture, being that only the trout, especially its holobiotic form, the brown trout, is cultivated for commercial purposes, in Portugal.