Invasive alien species in Switzerland - Schweizer ...

2 > Vertebrates – Vertebrata 57
The crucian carp (Carassius carassius (L.)) is probably native to Central and eastern
Europe, but was widely distributed by humans throughout western Europe in the
Middle Ages for fishing. It was in the recent past, if not still, being sold as a bait fish.
The crucian carp is a hardy species that can survive adverse conditions, such as low
oxygen levels and frost. It is also an Appendix 2 species, and therefore its use as a bait
fish is illegal. The crucian carp is rarely found in Switzerland.
The third Carassius species is the Prussian carp (Carassius gibelio (Bloch)). The
taxonomy of the three Carassius species is complicated and this species is sometimes
considered conspecific with C. auratus. The species are very similar in many ways,
including appearance, biology, food and potential impact. The actual distribution and
the history of introductions and spread are not well known, since the species were
probably often misidentified (Arnold, 1990). The Prussian carp is listed in Appendix 2,
thus its release outside contained captivity must be authorized.
The grass carp (Ctenopharyngodon idella (Cuvier & Valenciensis) (see Fact Sheet) is
of Chinese origin, but as it is one of the most important aquacultural fish, it has acquired
a wide distribution on five continents. Although natural reproduction has not
been reported in the wild in Switzerland, it is a species of concern because of its potential
to cause massive impacts on ecosystems by removing higher aquatic plants and
thereby causing shifts in the producer guilds to other plant species. This impact at the
bottom of the food chain can cause major alterations to ecosystems. The grass carp
showed some potential to control water weeds in Switzerland, but Müller (1995)
concludes that it only controls the symptoms of eutrophication instead of ameliorating
the causes of the deteriorating water quality. The grass carp is listed in Appendix 3 and
therefore all releases are prohibited.
The silver carp (Hypophthalmichthys molitrix (Valenciensis)) (see Fact Sheet) is a
highly specialized phytoplankton feeder. In many cases it was released to reduce
phytoplankton densities or stop algal blooms. Its origin is China, but today it is found
in many countries around the world. Spawning requires very specific conditions, but
has been recorded in the Danube. Its reproduction in Switzerland cannot be ruled out
with certainty, so the species was included in Appendix 3.
The stone moroko (Pseudorasbora parva (Temminck & Schlegel)) (see Fact Sheet) is
a very small cyprinid. It is the only established fish species accidentally introduced to
Europe and Switzerland, with shipments of grass carp from China. Whereas the deliberately
introduced fish species are of value to the commercial or sports sectors, the
stone moroko has no value to humans. Thus, the potential for conflicts over management
and legislative measures for the species is reduced and it is an Appendix 3 species.
The American catfish (Ameiurus melas and A. nebulosus (Le Sueur)) (see Fact Sheet)
belong to the family Ictaluridae, which is restricted to the subtropical and temperate
zones of North America, and were introduced into Europe to investigate their potential
as a fish for human consumption. However, they are of little value. The two species are