Pollution in rivers enhances the presence of the anchor worm in freshwater fish

The anchor worm is almost in all the planet and its spreading is associated with recreational activities in rivers and international commerce of fish for aquaculture. Image: U.S. Geological Survey
The anchor worm is almost in all the planet and its spreading is associated with recreational activities in rivers and international commerce of fish for aquaculture. Image: U.S. Geological Survey
Research
(17/06/2019)

Poorly treated waters that reach rivers and the runoff of agricultural areas can boost the spreading of the anchor worm -an exotic species that parasites freshwater fish- in the peninsular water network, according to a study in which the experts Alberto Maceda Veiga, from the Biodiversity Research Institute (IRBio) of the University of Barcelona, and Adolfo de Sostoa, from the Faculty of Biology and IRBio -have taken part.

Other participants in the article, published in the journal International Journal for Parasitology, are Ralph Mac Nally (University of Canberra, Australia), Andy J. Green (Doñana Biological Station, EBD-CSIC) and Robert Poulin (University of Otago, New Zealand).

The anchor worm is almost in all the planet and its spreading is associated with recreational activities in rivers and international commerce of fish for aquaculture. Image: U.S. Geological Survey
The anchor worm is almost in all the planet and its spreading is associated with recreational activities in rivers and international commerce of fish for aquaculture. Image: U.S. Geological Survey
Research
17/06/2019

Poorly treated waters that reach rivers and the runoff of agricultural areas can boost the spreading of the anchor worm -an exotic species that parasites freshwater fish- in the peninsular water network, according to a study in which the experts Alberto Maceda Veiga, from the Biodiversity Research Institute (IRBio) of the University of Barcelona, and Adolfo de Sostoa, from the Faculty of Biology and IRBio -have taken part.

Other participants in the article, published in the journal International Journal for Parasitology, are Ralph Mac Nally (University of Canberra, Australia), Andy J. Green (Doñana Biological Station, EBD-CSIC) and Robert Poulin (University of Otago, New Zealand).

 

Anchor worm: an invasive crustacean that came from the Asian continent

The anchor worm (Lernaea cyprinacea) is an invasive species from Asia that affects freshwater fish -cyprinids and salmonids, in particular- and causes many economic losses in fish farms. In the peninsula, this copepod crustacean was first identified in 1973 in River Esla, in León. Today, the anchor worm is almost in all the planet and its spreading is associated with recreational activities in rivers and international commerce of fish for aquaculture.

“The parasitic fauna -native and exotic- affecting freshwater fish in the peninsula is still quite unknown, especially the cyprinids, the most common family of fish in the peninsula and the European continent”, says Alberto Maceda, member of IRBio and EBD-CSIC. 

“Freshwater fish are one of the most threatened animal group worldwide -he continues- and one of the factors could be their growing vulnerability regarding pathogens that enter natural ecosystems”.

The new study assesses those factors associated with episodes of parasitism in L. cyprinacea in nineteen fish species (carp, common trout, eel, barbell, mosquitofish, etc.). In particular, the experts analyse how changes affect the quality of water and the natural habitat in the dispersal of the anchor worm in hydrographic basins in the northern eastern area of the peninsula -Catalonia, Ebro River and Garona River- which are affected by common environmental stress factors in a great part of the water systems worldwide.

Climate change: could it favour the presence of the anchor worm?

The anchor worm is present in all the analysed hydrographical regions, except for the basins of RIdaura, Sènia, Garó and Foix in Catalonia.

 

Pollution due nutrients and high conductivity of water -non-treated waste waters- are factors that boost those cases of parasitism in the anchor worm in the water system, according to the experts.

Environmental pollutants can affect the immune system of local fish and turn them more sensitive to parasite infections. When the parasite tolerates toxics, it takes advantage of the situation and parasites in weak fish. “It is worse if the parasite is an exotic organism and the immune system of native fish has not evolved with the introduced species. Then, infections can have fatal effects”, warns Alberto Maceda.  

Freshwater fish with high rates of parasite infections belong to five native species: the Catalan barbel (Barbus haasi),   the Ebro barbel (Luciobarbus graellsii), the Ebro nase (Parachondrostoma miegii) and the Catalan chub (Squalius laietanus). Among the most affected fish by the worm are the carp (Cyprinus carpio) and the pumpkinseed (Lepomis gibbosus), exotic species.

The shape of the fish and location of the water area are other factors that can boost the presence of this general parasite, which is usually in the lowest areas of the water course where temperatures are warmer. 

“However, finding the anchor worm in river trouts -colder waters- makes us think about the potential impact of the climate change on the expansion of this invasive species”, warns Maceda.

Water Framework Directive: protecting biodiversity in water systems

Prevention is determining to stop the spreading of the anchor worm in the peninsular water network, the experts warn. It is common for parasitism cases caused by this infectious agent to be unnoticed -with low infection percentages- except for unexpected epidemic outbreaks, which can cause the massive death of fish. “Once we reach this limit, it will be too late to act and we will not be able to do anything to save the fish population”, notes Maceda.

In the future, it will be decisive to improve the environmental state of rivers, avoid the transfer of fish -they can be parasite vectors- among different traces, and disinfect waters in companies, to stop the expansion of the parasite worm in the water network.

“Regarding this threatening situation, we should fulfil with no exception the EU Water Framework Directive in all water sections, and not only thinking on the impact of the parasite worm but also on the benefits for the rivers in general, natural ecosystems and society in general”, conclude the authors Alberto Maceda and Adolfo de Sostoa.