DNA of Dutch carp under threat
The crucian carp, the only cyprinid native to the Netherlands, can crossbreed with non-native carp species. That’s one of the things Sebastiaan Rückert, Master’s student at the University of Amsterdam (UvA), discovered during his research for the RAVON Foundation (Reptilian, Amphibian and Fish Research Netherlands). He found genetic changes in the crucian carp which could, in the long run, cause this rare species to become extinct.
The crucian carp (Carassius carassius) is the only cyprinid native to the Netherlands. Its numbers have dwindled in recent years due to the disappearance of small streams from wetlands and flood plains. But changing habitats aren’t the only threat to this vulnerable carp species, Rückert found.
His research was prompted by findings from neighbouring countries which show that cyprinids are able to crossbreed. Rückert decided to set up a similar study in the Netherlands. Because different carp species are hard to tell apart with the naked eye, they had to be examined at DNA level. With a fishing rod and net, Rückert and his RAVON colleagues collected specimens from ten carp populations and took samples from their fins. The subsequent lab work at the UvA, where supervisors included lecturer Hans Breeuwer, consisted of analysing the mitochondrial and ribosomal DNA.
The findings show that crossbreeding with the common carp does indeed take place. One of the sampled crucian carp populations consisted almost entirely of hybrids of crucian and common carp. Though this was not the case for the other populations, common carp, goldfish and Prussian carp were found in abundance, which is an indication that an invasion of non-native carp species may be taking place.
Origins of exotic species
Rückert explains that the presence of these exotic species results from the fact that ‘the Dutch anglers’ association releases common carp into open waters every year, and hybrids of common carp and goldfish in closed waters. It was assumed that these hybrids were infertile, but research in Australia and the UK has proven otherwise.’ The study conducted in the Netherlands has now confirmed these earlier findings.
With this study completed, Rückert wants to take things to the next level. ‘Two locations where the analysis showed hybridisation clearly taking place were Zandvoort aan Zee and Zwaag. Further research could be undertaken here into the fertility of the hybrid individuals, how they’re reproducing and the extent of gene transfer. That could give us more of an idea of what’s actually going on in Holland’s underwater world.’
Sebastiaan Rückert is Master's student Ecology & Evolution at the University of Amsterdam. He cooperated for his research with Frank Spikmans, Arthur de Bruin and Martijn Schiphouwer from RAVON, and Dick Roelofs from the VU University. At the UvA Hans Breeuwer, Peter Kuperus and Betsie Voetdijk supervised the research project.