I found this study doing a search on Google.
Control of Predacious Flatworms Macrostomum sp. in Culturing Juvenile Freshwater Mussels
Lora L. Zimmerman and Richard J. Neves
Virginia Cooperative Fish and Wildlife Research Unit,1 U.S. Geological Survey, Department of Fisheries and Wildlife Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061-0321, USA
Doug G. Smith
Department of Biology, University of Massachusetts, Amherst, Massachusetts 01003-5810, USA
Abstract.â€"Flatworms of the genus Macrostomum are voracious predators on newly metamorphosed juvenile freshwater mussels (Unionidae), which require a fish host to transform mussel larvae into free-living juveniles. Toxicity tests were performed with formalin (paracide-F, 37% formaldehyde) to determine the appropriate levels of treatment for eradicating these flatworms from host fish tanks without adversely affecting the culture of juvenile mussels. Results indicate that a 1-h shock treatment of 250 mg/L formalin or a 3-d continuous exposure to 20 mg/L of formalin kills adult Macrostomum but not fish. Observations indicate that a single treatment is insufficient to kill Macrostomum eggs, so a second treatment after 3 d is necessary to kill newly hatched flatworms. Newly metamorphosed freshwater mussels exposed to similar shock and continuous treatments of formalin were also killed. Thus, all host fish introduced for the purpose of mussel production should be quarantined and treated prophylactically to avoid the infestation of mussel culture systems with predacious flatworms.
Received: February 28, 2002; Accepted: July 1, 2002