The Habitat Suitability Index (HSI) is a quantitative index that determines the capacity of a given area to meet habitat requirements for a specific species with respect to given variables. The degree of universality of this index is not well understood yet. The purpose of this work is to present the results of a literature data re-analysis of HSI for brown trout and demonstrate the existence of a universal level of similarity in the ranges of hydraulic variables for the considered species.