The huge mussels, reaching 22 to 26 cms. in size which appeared along the bank of the Danube in Rousse about a fortnight ago, have been proved to be an invasive mussel species from China, Radio Varna reports.

Biodiversity and ecosystems experts from the Bulgarian Academy of Sciences say they are Chinese pond mussels. They were first spotted in the Danube in 2005 but since then, the population of the species has exploded.

The Chinese pond mussels are not a direct threat to the other animal species but they do attack their direct Bulgarian rivals – two species of pond mussels – by reducing their feed resources. The invasion was first noticed in the first half of August when the temperature of the water rose.