In situ and low-cost monitoring of particles falling from freshwater animals: from microplastics to parasites

A simple and low-cost method of monitoring and collecting particulate matter detaching from (or interacting with) aquatic animals is described using a novel device based on an airlift pump principle applied to floating cages. The efficiency of the technique in particle collection is demonstrated using polyethylene microspheres interacting with a cyprinid fish (Carassius carassius) and a temporarily parasitic stage (glochidia) of an endangered freshwater mussel (Margaritifera margaritifera) dropping from experimentally infested host fish (Salmo trutta). The technique enables the monitoring of temporal dynamics of particle detachment and their continuous collection both in the laboratory and in situ, allowing the experimental animals to be kept under natural water quality regimes and reducing the need for handling and transport. The technique can improve the representativeness of current experimental methods used in the fields of environmental parasitology, animal feeding ecology and microplastic pathway studies in aquatic environments. In particular, it makes it accessible to study the physiological compatibility of glochidia and their hosts, which is an essential but understudied autecological feature in mussel conservation programs worldwide. Field placement of the technique can also aid in outreach programs with pay-offs in the increase of scientific literacy of citizens concerning neglected issues such as the importance of fish hosts for the conservation of freshwater mussels.