Duck mussel

Anodonta anatina

On guided boot tours of the Donau-Auen National Park, living Duck mussels may sometimes be observed, or at least traces of what were once living specimens may be found in the mud.

Description
All bivalve molluscs share the characteristic of a house made of two calcareous shells. The inside of the common Duck mussel has only minimal mother-of-pearl coating. The shell has an oval, rhombic form and is normally quite thick all the way through, with a size of up to 10cm. The scute, or scale-like external plate, has a pronounced triangular angle. Living organisms exhibit wide gapes.

Distribution
Anodonta anatina is widespread in Central Europe and populates the waters of the Donau-Auen National Park.

Endangerment and Conservation Status
According to the Austrian Red List, this type of mussel may be a near threatened (NR) species.

Behaviour
As a bottom feeder this mollusc uses its foot to move along the ground at water's bottom. The foot also serves as an anchor in soft or sandy sediment. By stirring up the bottom sediment the mussel can filter out nutrients from the water with its gills. It feeds primarily on organisms living at the bottom such as small algae and cyanobacteria. But detritus (dead plant and animal matter) may also be on the menu. The more polluted the waters, the greater the danger for this species. Another threat to the Duck mussel – and all mussels – is human intervention in the form of river regulation, dam building and other destruction of natural wetlands habitats. The straightening and excavating of rivers and streams destroys the natural habitat of resident mussels. Mussels are also extremely sensitive to changes in location.
Of all native Anodontinae freshwater mussels, the Duck mussel tolerates the largest variations in types of water habitats. Whether muddy or sandy, stagnant or slow-moving, the Duck mussel adjusts to whatever water characteristics it finds. Yet environmental factors are decisive when it comes to lifespan: in waters rich in food such as is found in the Donau-Auen National Park, the Duck mussel matures more rapidly yet does not live as long as in colder, nutrient-poor waters.
In contrast to other types of freshwater mussels, there are separate sexes, male and female. In order to reproduce the Anodonta anatina deposits up to 400,000 glochidia (mussel larvae) in the water in the spring. The larvae have robust hooks with which they latch on to a host fish. There is no one type of host fish favoured by the Duck mussel, and thus the host may be a chub, perch, dart, rudd, pike, moderlieschen or other fish species.

Special Characteristics
The fact that this mussel used to be very common in the region is evident from one of the alternative German names for the Duck mussel, the "Common Duck mussel". Because there used to be such large and widespread populations of this mussel, it was often used as duck feed. This led to the most often used name, the Duck mussel.