Integrating genetics and ecology towards the conservation of the bullhead (Cottus gobio) and the stone loach (Barbatula barbatula), two native freshwater fish species

To date, information on the level or distribution of genetic diversity within fish species inhabiting anthropogenically disturbed Flemish rivers is virtually absent. In addition, knowledge of habitat improvement techniques, the barrier-effect of human structures and/or the effectiveness of fish pass facilities is also lacking for many native species, especially those with no economical or recreational importance. Information concerning the above topics is however of vital importance to develop sound species-specific conservation programmes. The objective of this thesis was to contribute to the elimination of this lacuna for the bullhead (Cottus gobio) and the stone loach (Barbatula barbatula), two small bottom-dwelling freshwater fish species that have suffered a (considerable) decline during the twentieth century in Flanders and other parts of Europe.; Despite extensive human activities during the twentieth century, high levels of genetic diversity at microsatellite loci were detected in the investigated Flemish stone loach populations (HE: 0.67--0.85; MNA: 6.2--11.2). Conversely, analysis of microsatellite loci indicated that levels of genetic diversity in Flemish bullhead populations often were (extremely) pauperised (HE: 0.01--0.68; MNA: 1.1--6.0). In addition, there were indications that bullhead populations that have been depleted of genetic diversity were also suffering a decreased fitness. It is highly unlikely that the major degradation of the Flemish watercourses during the twentieth century did not significantly contribute to the observed genetic decay in the examined bullhead populations. After all, the species is not only considered to be very sensitive to water pollution but also to river engineering practices.; The current size of bullhead populations appears to be very important for the maintenance of genetic variation within a local population. Consequently, to minimise or even reverse further genetic erosion, an immediate priority for conservation should be to increase the size and range of the remaining bullhead populations. Essential requirements to achieve this are improvement of the habitat quality and reduction of the river fragmentation.; Vital habitat components for the survival of the bullhead are stones or other hard substrates (they are used as spawning and shelter sites). (Abstract shortened by UMI.)...