Ichthyofauna in the upper Rhine River close to the city of Karlsruhe as determined by the analysis of fish impingement by cooling-water intakes of a power plant

AbstractThe fish fauna in the northern part of the upper river Rhine close to the city of Karlsruhe (Germany) was analyzed by collecting fish from the cooling-water intake of a power plant (impingement method) between 1989 and 2001. With this method a total of 36 fish species were recorded. The results were compared between the years as well as with other studies on the fish fauna in this area. Particularly with regard to the physical structure of the river bed and banks, the pre-technical situation of the river Rhine has not been restored. However, the number of fish species has been augmented since the 1970s mainly due to improvements in the water quality and almost all autochthonous fish species are present again. Altogether only three introduced fish species (Sander lucioperca L., Lepomis gibbosus L., and Carassius auratus gibelio were found in this study. Among the long-distance migrating species three freshwater spawners (Lampetra fluviatilis, Petromyzon marinus and Salmo trutta trutta) were detected in addition to the catadromous eel. The eudominant fish species varied between years, i.e. the European eel, Anguilla anguilla, was the eudominant species 1989, whereas this species occurred in much lower numbers during the subsequent sampling campaigns. This clearly indicates that the high dominance of eels is mainly caused by stocking activities in the upper Rhine. In the following years roach, Rutilus rutilus was the eudominant fish species. Overall a positive development of the fish fauna in the upper Rhine over the last 15 years could be observed in terms of fish populations as well as in terms of species richness

Merging species? Evidence for hybridization between the eel parasites <it>Anguillicola crassus</it> and <it>A. novaezelandiae</it> (Nematoda, Anguillicolidea)

<p>Abstract</p> <p>Background</p> <p>The eel parasitic nematodes <it>Anguillicola crassus</it> (originating from Asia) and <it>Anguillicola novaezelandiae</it> (originating from New Zealand) were both introduced to Europe, but occurred in sympatry only in Lake Bracciano in Italy, where they both infected the European eel (<it>Anguilla anguilla</it>). <it>A. novaezelandiae</it> was introduced to the lake in 1975 and disappeared soon after <it>A. crassus</it> was also found there in 1993. We tested the hypothesis if hybridization of the two species might be an explanation for the findings at Lake Bracciano.</p> <p>Findings</p> <p>After laboratory infection of one European eel with 10 third stage larvae of each parasite, two living female and 4 male adults of each species were found to co-occur in the swim bladder after 222 days post exposure. In 9 out of 17 eggs, isolated in total from uteri of the two <it>A. novaezelandiae</it> females, alleles were detected by microsatellite analysis that are characteristic for <it>A. crassus</it>, suggesting the hybrid origin of these eggs. In contrast, none of the eggs isolated from <it>A. crassus</it> females possessed alleles different from those found in <it>A. crassus</it> adults, but it was revealed that one female can be inseminated by several males.</p> <p>Conclusion</p> <p>Our results show that <it>A. crassus</it> and <it>A. novaezelandiae</it> can co-infect a single eel and can mature together in the same swim bladder. We also provide evidence for the possibility of hybridization of <it>A. crassus</it> males with <it>A. novaezelandiae</it> females. Therefore, hybridization might be an explanation for the disappearance of <it>A. novaezelandiae</it> from Lake Bracciano.</p