Golden mussel: native fish help control the invader in Paraná

The golden mussel has become one of the most troublesome invasive species in Brazilian waters, establishing colonies that can clog hydroelectric pipes and water-intake systems. In Paraná, research by the Centre for Research in Limnology, Ichthyology and Aquaculture at the State University of Maringá, Nupélia/UEM, shows that some local wildlife has found a way to make use of the invader: several native fish have added the mollusc to their diet.

How did the golden mussel colonise Brazilian rivers?

Native to Asia, the mollusc arrived in South America in the early 1990s, mainly through ships’ ballast water. It subsequently spread through the Plata Basin, reached the Itaipu Reservoir and then the Upper Paraná River floodplain, expanding through habitats suitable for reproduction.

One of its greatest advantages is its ability to attach securely to hard surfaces. Thousands of individuals may cover rocks, concrete structures, sluice gates and pipes, restricting water flow and raising maintenance costs at hydroelectric plants, water-treatment facilities and other installations.

• It creates colonies containing large numbers of individuals;
• It attaches to rocks, concrete, metal and pipes;
• It spreads readily through connected rivers and reservoirs;
• It competes with native organisms for space and food;
• It can cause operational issues in infrastructure that uses water.

Which native fish have begun eating the invader?

Research carried out in the Itaipu Reservoir found golden mussels in the digestive tracts of several species. Fish that have begun using this new food source include piapara, armado catfish, black armoured catfish and pacu, showing that local wildlife can incorporate a relatively recent invasive species into the food chain.

Does eating golden mussels mean their population is controlled?

Not necessarily. Effectiveness depends on how many are eaten and, above all, on each fish’s ability to break the shell. Piapara and some armoured catfish can crush hard structures while feeding, making it more likely that the mussels they consume are actually destroyed.

Armado catfish display more complex behaviour. Although they can eat large quantities of the mollusc, researchers have found specimens with intact shells in their digestive systems. In other words, merely finding mussels inside a fish is not enough to conclude that the species controls them effectively.

• Piapara can crush some shells while feeding;
• Armoured catfish have structures suited to feeding on organisms attached to the bottom;
• Armado catfish eat mussels but do not always destroy them completely;
• Pacu can also include the invader in its diet;
• Predation intensity differs between species, sizes and environments.

What does recent research show about this natural control?

Experiments and food-web analyses suggest that the golden mussel has already become an important food source for certain fish in reservoirs across the Paraná Basin. Experimental work involving piapara even recorded a reduction in mollusc biomass when the fish were present, supporting the idea that some native predators can place pressure on their populations.

Can fish alone stop the golden mussel from spreading?

Natural predation cannot eliminate the golden mussel from rivers and reservoirs where it has already become established. Its high reproductive capacity and ability to disperse mean that conserving wildlife must be combined with monitoring, preventing its transfer to new basins, and specific measures to protect water-supply and power-generation systems.

However, native fish provide an important additional biological barrier. Piapara, armoured catfish and other consumers continually remove individuals from the environment and help incorporate the invader into the food chain. Protecting these populations in Paraná’s rivers may strengthen a natural control mechanism and, at least locally, lessen the pressure caused by one of the country’s most difficult aquatic invasions to manage.