Freshwater mussels (Anodonta anatina) reduce transmission of a common fish trematode (eye fluke,Diplostomum pseudospathaceum)

Abstract

Recent results suggest that bivalves can play an important role in restraining the spread of various aquatic infections. However, the ability of mussels to remove free-living stages of macroparasites and reduce their transmission is still understudied, especially for freshwater ecosystems. We investigated the influence of the common freshwater mussel (Anodonta anatina) on the transmission of a trematode (eye fluke, Diplostomum pseudospathaceum), which frequently infects fish in farms and natural habitats. In our experiments, mussels caused a significant decrease (P < 0·001) in the abundance of trematode free-living stages, from 6520 to 1770 cercariae L-1 on average (about 4-fold in 2 h). Individual clearance rates of mussels were 0·6‒3·7 L per hour (mean 1·9). These tests were followed by experimental infections of rainbow trout (Oncorhynchus mykiss) with different doses of D. pseudospathaceum cercariae in the presence or absence of mussels. Exposure of fish to cercariae in the presence of mussels significantly (P < 0·05) reduced the infection intensities in fish (by 30-40%) at all exposure doses. Our results indicate that freshwater bivalves can markedly reduce local cercariae densities and could be useful in mitigation of trematodoses harmful to fish farming.

Parasite transmission in aquatic ecosystems under temperature change: effects of host activity and elimination of parasite larvae by filter‐feeders

“…Importantly, though cercariae are effectively removed from the water by Anodonta mussels, they are probably transformed into pseudofeces and poorly ingested like the similar-sized filamentous cyanobacteria (Bontes et al 2007). Ingestion of cercariae by mussels and other filter-feeders is questionable and needs further investigation, while there is no doubt that filter-feeders can effectively eliminate parasite free-living stages and reduce their density in water (Gopko et al 2017a).…”

“…In half of the containers in each heating treatment, we placed live A. anatina (one mussel per container), while closed empty A. anatina shells served as controls. Empty shells and switched-off heaters were put in containers to minimize the difference in fish behavior between the treatments (Gopko et al 2017a). Therefore, there were the following treatments: 1) containers with heating and the presence of live mussel (H+M+), 2) containers with heating and the presence of empty shell, i.e.…”

“…However, the temperature rise may also influence ecosystem processes, which can hamper transmission success of parasites, such as removal of parasite infective stages by natural enemies. Free-living stages of parasites comprise a substantial share of the biomass in aquatic ecosystems (Kuris et al 2008, Lafferty et al 2008, and many aquatic organisms eliminate parasitic larvae, thus, significantly reducing infection transmission (Thieltges et al 2008, Johnson et al 2010, Welsh et al 2014, Gopko et al 2017a. Feeding rates of poikilothermic organisms are strongly temperature-dependent like most metabolic processes (Schmidt-Nielsen 1997).…”

Trematode cercariae as prey for zooplankton: effect on fitness traits of predators

“…Thus, almost all groups of benthic organisms (e.g. carnivorous plants, cnidarians, turbellarians, oligochaetes, bryozoans, mollusks, crustaceans, insect larvae, fishes) were reported to consume free-living stages of parasites (reviewed in Thieltges et al , 2008 a ; Johnson et al , 2010; Orlofske et al , 2015; Gopko et al , 2017 a ).…”

“…The key role of zooplankton in aquatic food webs and high biomass and nutritional value of trematode cercariae (Thieltges et al ., 2008 b ; Preston et al ., 2013) suggest that these trophic links could be important. Removal of free-living stages of parasites by predators can strongly reduce parasite transmission in aquatic ecosystems resulting in decreased infection intensities and prevalences in host organisms (Schotthoefer et al ., 2007; Orlofske et al ., 2012; Gopko et al ., 2017 a ).…”