Most bivalves (mussels, clams, scallops, etc.) are filter feeders, meaning they obtain nutrients by filtering their food out of the water. They use asiphon to suck in waterand use tiny hairs (cilia) totrap food particlesbefore siphoning the water back into the environment. Some species can beprodigious feeders: a clam the size of your thumbnail can filter6 L of water each hour.
The focus of this weeks’ blog is on a recentstudythat tested whether the natural feeding behaviour of theduck mussel(Anodonta anatine), a common freshwater species found innorthern Europe and Asia, could help reduce the number of trematode parasites in water.
The trematode parasite that was used in this study is theeye fluke(Diplostomum pseudopathaceum). Infected freshwater snails (i.e.Lymnea stagnalis) can produce tens of thousands of free swimming larval cercariae which then infect fish. The parasite can infect abroad range of fish species; the parasite migrates to the eye and develop into metacercariae. The life cycle is completed when a bird consumes an infected fish and the parasites develop into adults and reproduce sexually in the intestine (Figure 1).
Gopko and colleagues第一个测试贻贝是否会减少麻木er of free swimming cercariae in aquarium. They measured the number of free swimming cercariae after 2 hours in an aquarium with mussels. Originally, there were 6000 cercariae/L in each container. Mussels were left in the containers for 2 hours and the remaining cercariae numbers were estimated from 3 5-ml aliquots. In all cases, mussels significantly reduced the amount of free swimming larvae over 2 hours (on average 4- fold decrease). It is not known if this is due to ingestion or if the mussels were mechanically damaging the cercariae.
Next, the authors looked to see if the mussels could affect transmission to rainbow trout. Trout, with and without mussels were placed into tanks with three different densities of cercariae. At all three densities; there was lower infection rates of eye flukes on fish in tanks with mussels present (Figure 2).
What does this mean for the future of bivalves as disease control agents?
These results support several other studies that have shown that various species of bivalves can filter outbacteria,virusesand evenparasitesin a range of aquatic environments. Fewer studies have demonstrated that filtering caninactivate parasites, reducing onward transmission. The recent study described here supports this body of literature and expands the number of systems where bivalves can help reduce parasite transmission.
The impressive filtering abilities of bivalves has not gone unused over the years. They have been used to measurebioaccumulationat local sites. The most famous example is theMussel Watch Programmethat started using mussels and oysters along coasts and lakes in the US in 1986 to monitor accumulation of pollutants. They are now used worldwide for monitoring metal and pollutant accumulation. Maybe next on the list is reducing disease?
This study, and others, point to a role for bivalves in controlling disease, especially amongst high density transmission settings like commercial fish farms. However, bivalves can also contribute to disease transmission; many species act as hosts for otherpathogensandparasites. Before bivalves are considered for disease control, it will be important to understand the biology of the particular species and potential diseases it could carry or its potential to become invasive before being used for control of eye flukes or other diseases.
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