Killer 'shrimp' invades Cambridgeshire reservoir

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A highly invasive amphipod has been discovered by anglers living in the Grafham Water reservoir, Cambridgeshire - the first time this species has been recorded in the UK.

The Environment Agency was sent specimens by the concerned fishermen and confirmed it is Dikerogammarus villosus, often erroneously described as the killer freshwater 'shrimp'.

The find is a particular worry as this carnivorous crustacean grows around 50% larger than the UK native freshwater 'shrimp' species, Gammarus pulex and is a voracious predator, preying on everything from small fish and fry, damselfly nymphs and water boatmen as well as the native Gammarus.

The effect this invader may have on the fragile balance of UK freshwater ecosystems is unknown, but there are fears it could have a similar impact in rivers here as it already has had in its seemingly unstoppable spread across mainland Europe.

Studies in the Netherlands have shown it capable of not only wiping out the native Gammarus duebeni, but also the previously extremely successful North American invasive species Gammarus tigrinus.

Dikerogammarus villosus is native to the Ponto-Caspian region of the Eurasian steppe. It grows to around 30mm and is far more predatory than native Western European amphipods which are largely detritivores. With larger and more powerful mouthparts, it kills its prey by biting and shredding and has been observed to kill indiscriminately, often not even eating its victims.

It is able to colonise a wide range of habitats, being able to withstand significant fluctuations in temperature, oxygen levels and salinity.