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Pathways in Animal Invasions 21
waters (Chap. 16), and other native species (Drake and Naiman 2000). Similarly,
the North American largemouth brass Micropterus salmoides was
released throughout the world for fishing (also among the 100 world’s worst
invaders), and the East European pike-perch (Sander lucioperca) now also
occurs in Western Europe, including England. The American catfish Ameiurus
melas and A. nebulosus were introduced into Germany in the 19th century for
aquaculture, were subsequently found to be not valuable as food but were
soon spread all over Europe.
In the 1950s, the Nile perch (Lates niloticus), native to North and West
African river systems, was released into Lake Victoria and other East African
lakes, and soon became of great commercial importance as a food item. Being
a strong predator on all organisms in its ecosystem, only 20–30 years later,
60 % of the 300 endemic Haplochromis cichlid species were extinct. Today, it is
considered as one of the world’s 100 worst invasive species (Schofield 1999;
Verschuren and Johnson 2002). In the early 1980s, the eel parasite Anguillicola
crassus was introduced with transports of eel (Anguilla sp.) from Southeast
Asia to Europe and also to North America. This parasite spread in Europe
within two decades, and it affects not only the natural European eel populations
but also the aquaculture of eels (Peters and Hartmann 1986).
Several crayfish species from North America were introduced into Europe,
with the aim of growing these in farms, e.g. Pacifastacus leniusculus, Procambarus
clarkii and Orconectes limosus. Some escaped or were released, and are
now widespread in Europe, transferring the crayfish plague, the fungus
Aphanomyces astaci, to native crayfish species which are much more susceptible
and often have become locally extinct. The fungus is one of the 100
world’s worst invaders.
Comparably, many mussel and oyster species, distributed worldwide for
mariculture, escaped. The Mediterranean mussel Mytilus galloprovincialis
now replaces native species in South Africa and parts of the United States.
Also, frogs such as the North American bullfrog, Rana catesbeiana, have been
released as harvestable game animals for food. The East African giant snail,
Achatina fulica, became established all over the tropics because it was transported
for food purposes, escaped from gardens, was intentionally released or
was moved with agricultural products, equipment, cargo, plant or soil matter.
A. fulica was also introduced into many areas for its use in medicinal remedies.
The latter three species belong to the list of the 100 world’s worst
invaders (ISSG 2006).