THE FISH FAUNA OF THE DOUBS RIVER PRIOR TO COMPLETION OF THE RHINE-RHONE CONNECTION

The part of the Doubs River between Montbeliard and Dole (France), i.e ., downstream from the confluence with the Allan River, will be affect ed by the Rhine-Rhone connection project. In order to improve the unde rstanding of the Doubs ichthyofauna, aquatic environments of the Doubs were sampled by electrofishing. Fish diversity and the presence of so me rheophilic species demonstrated the good ecological quality of some stretches of the Doubs. This quality was due to alternating areas wit h very diversified aquatic environments (riffles, islands and side-arm s, back-waters) and a considerable range of flow velocities. The diffe rences in the structure of the fish communities of the different types of aquatic environments were more qualitative (fish species) than qua ntitative (number of species and number of fish). However, the mean nu mber of fish was statistically lower in the canals (Freycinet canal an d channelized part of the Allan River) than in the main course and in the backwaters. The natural parts of the Doubs (unnavigable reaches) s howed the most diversified environmental structure and had the most rh eophilic fish communities. Thus, the rheophilic species were well repr esented, but they proved also the most vulnerable to river regulation. However, the most abundant fishes throughout the Doubs River were gen eralists with no special requirements for food sources or spawning sub strate.