Investigations on the use of subfossil remains (i.e. Chironomidae and Cladocera) to evaluate the effects of fish introductions on the invertebrate communities in lakes, are here presented. The abundance and size of the ephippia of Daphnia (Cladocera), which may vary in response to fish predation pressure, are analysed in four mountain lakes of the Pyrenees. Also, changes in chironomid communities that could be potentially attributed to fish introductions are evaluated in the same lakes. The latter may be triggered directly through predation on more visible chironomids; or indirectly, through the effect of fish on lake nutrient re-cycling, which may increase organic matter content in lake sediments, thus favouring some chironomids more than others. Results are presented for lakes in the Haut Vicdessos valley (French Pyrenees), where fish introductions began during the mid XX century.