This freshwater crayfish, Procambarus clarkii, is native to the southeast of the U.S., but also found in many other ecosystems as an invasive species. (Photo : Wikimedia Commons )

Invasive species are escaping from aquaculture facilities -- those that farm fish or shellfish -- and being inappropriately released into European rivers and lakes, according to a recent study. Researchers from the Joint Research Centre (JRC) are calling for tightened controls and increased mediation to manage the introduction of alien species.

For their study, researchers examined the trends of over 750 invasive freshwater fish using the JRC's European Alien Species Information Network (EASIN). In doing so they found three main gateways: Germany, the United Kingdom and Italy, according to a news release.

Generally speaking, when invasive species are introduced to a new area they do more harm than good. This is particularly unfortunate in the case of freshwater ecosystems, which are already experiencing high rates of biodiversity loss resulting from human activities. This includes pet and aquarium trade fish and other creatures being released, and other stocking activities. In Europe alone, researchers found freshwater-alien species introductions have drastically increased over the past 60 years.

Much of the initial invasion is a result of European aquaculture, which is one of the fastest-growing sectors of the world food economy, researchers noted. However, aquarium trade is also a leading factor and considered a multi-billion dollar industry.

When a species enters a new habitat range they may not encounter any natural predators. In turn, this allows for a widespread takeover, in which the invasive species establishes themselves and breeds rapidly. Most of the time, many native species lack defenses against the invaders and suffer from increased food competition. Twenty percent of species extinctions are caused by invasive species.

However, researchers suggest that public awareness and stricter regulation may help minimize the impact alien species have on native habitats. Their study was recently published in the journal Aquatic Invasions.

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