Guppies in Gillbach

Funded by the GfI

Research on invasive tropical fish in Germany – The Gillbach/Erft system

In addition to geothermally heated springs, bodies of water that are thermally polluted by human activities have also attracted the interest of scientists in recent decades.

One example is the Gillbach, which flows through the Rhine valley – little here reminds us of the tropics – and yet guppies, antenna catfish and, more recently, marbled cichlids feel at home in the waist-deep stream, hibernating and reproducing. Scientists from the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) and two other Leibniz Institutes are researching in the Gillbach how the cooling water discharge from the nearby coal-fired power plant and released aquarium fish are affecting the stream’s ecosystem. To anticipate the punchline: aquarium fish do not belong in native waters.

Impressions – Top left: The Gillbach is regularly examined for fish fauna using nets. Top centre: Gregor Kalinkat and Friedrich Wilhelm Miesen in front of an authentic backdrop. Top right: Tilapia mariae from the Gillbach – a population of all age groups was identified. Bottom left: Catch-recapture experiments with UV-colour-marked guppies made it possible to determine their population size – there are several thousand individuals in the first 500 metres in summer. Bottom right: Guppies from the Gillbach.

This watercourse is so special because, especially in its upper reaches, it has a water temperature of over 20 °C all year round, providing a habitat for a community of animals and plants that would not otherwise occur naturally in Germany. This is due to the inflow of warm cooling water from the Niederaußem lignite-fired power station. According to reports, the first guppies were found in the Gillbach shortly after the coal-fired power station went into operation. Initial scientific fishing in 1998 provided a more comprehensive picture of the species present in the Gillbach: five native species and seven exotic species were identified. In addition to the guppies, antenna catfish and marbled cichlids already mentioned, there are also populations of Nile tilapia, zebra cichlids, Neocaridina and Macrobrachium shrimp, as well as tower cap snails and extensive Valisneria stocks. Occasionally, goldfish or koi can also be seen.

Since 2011, the Alexander Koenig Zoological Research Museum in Bonn has been conducting annual fishing surveys. This allows us to determine which species have been able to establish themselves in the Gillbach or regularly find their way there. These are probably mainly abandoned aquarium animals that became too much for their owners, because apart from tilapia, all the exotic species found in the Gillbach are popular aquarium inhabitants or, as in the case of goldfish and koi, pond inhabitants. The tilapia, known as food fish, probably originate from a disused aquaculture facility that once also used the warm water of the Gillbach. The system is of great scientific value, as it allows invasion and spread processes to be studied in detail.

Species descriptions in the GfI Fish Atlas

Guppy Poecilia reticulata Peters 1859

Zebrabuntbarsch Amatitlania nigrofasciata (Günther 1867)

Background photo: David Bierbach, GfI

Funded by the GfI

Research on invasive tropical fish in Germany – The Gillbach/Erft system

More information on this topic can be found in the following publications:

Species descriptions in the GfI Fish Atlas