This presentation describes a series of experiments designed to study the biology and fisheries of decapod crustaceans in the Western Mediterranean in the framework of research programmes carried out by Instituto de Ciencias del Mar (CSIC) in Barcelona. The results have been used to highlight the importance of bio-ecological studies on commercial species in instituting fisheries management programmes. A series of examples are used to demonstrate how integrating knowledge of the effects of biological and ecological aspects (growth, reproduction, migrations, aggregations, environmental factors, sexual dimorphism, behaviour, etc.) in the fisheries, is essential to avoid sampling errors and errors in stock assessment. Finally, potential directions for future research in this area are discussed.