Revue des sciences de l'eauContribution à la connaissance de la typologie ichthyenne des rivières ardennaises J. Dehove et C. Reizer SUMMARYQuantitative data about fish populations from a homogeneous faiogeagraphical environment, the Belgian Ardenne rivers, hâve been subjected to statistical analysis. This analysis was designed to détermine which statistical method(s) could be used to identify ichthyological groups (second-ordre hierarchy).Electro-fishing data were available for 140 sites ; élimination of polluted stations left 98 sites, and of thèse 84 were used for the statistical analysis. Four matrices were constructed frome the raw data : absolute and relative species fréquences ; absolute and relative species biomasses. Corrélation coefficients were used together with a hierarchical ranking method, based on chaining and principal component analysis (PCA). Methodological variations involved the selected data basis, sélection of distance, species position crîteria and chaining method.Application of PCA to the species frequency data yielded a primary axis (33 % explained variance) which separated suprarfieophilic and limnophilic species. The second, ttiird and fourtlt axes explained 14,10 and 8 % of the variance, respectively. Similarly, PCA analysis of the biomass data yielded a primary axis (25 % explained variance) separating suprarfieophilic and moderatewater species. The second, third and fourth axes explained 13,10 and 8 % of the variance. Projection of the structure in the 1-2-3 numericai sub-space (57 % of the information) is very expressive.Hierarchical analysis of the proximity of différent species led to the définition of the following socio-ecologicai groups : -Rheophilic supra brown front, bullhead medio minnow, stone-loach infra grayling, gudgeon, chub -Limnophilic supra common nose, dace, barbet, roach medio tench (with reserves)