Factors Affecting Survival and Growth of Juvenile Freshwater Mussels Cultured in Recirculating Aquaculture Systems

—Seasonal differences in glochidial maturity, substrate, and diet were studied to determine how these factors affect the survival and growth of juvenile freshwater mussels. Comparisons were made between juveniles produced in the fall and spring of the year; cultured in sediment, sand, or without substrate; and fed either of two species of small (5–10-mm) green algae. The survival and growth of endangered juveniles of oyster mussel Epioblasma capsaeformis were compared with those of a common, seemingly more robust species, the rainbow mussel Villosa iris. The growth of rainbow mussel juveniles was significantly greater than that of oyster mussel juveniles (P , 0.001). The survival and growth of oyster mussel juveniles were significantly greater when propagated in the spring, that is, when glochidia were mature and would normally be released, than in fall (P , 0.001). Survival and growth of juveniles of both species were significantly greater when they were cultured in a sediment substratum rather than sand or no substratum (P , 0.001). No differences (P . 0.05) were observed in survival and growth of juveniles fed algal species Neochloris oleoabundans or Nannochloropsis oculata. In the spring of the year, juvenile oyster mussels achieved a survival of 29.6% and mean length of 664 mm at 60 d of age, whereas at the same age rainbow mussel juveniles exhibited a survival of 25.1% and a mean length of 1,447 mm. North America contains the greatest diversity of freshwater mussels in the world, nearly 300 species. However, bivalve mollusks of the superfamily Unionacea are the most imperiled group of animals in the United States, with 213 species (72%) listed as endangered, threatened, or of special concern (Williams et al. 1993; Neves 1999). Already, approximately 35 species are considered extinct, representing 12% of the North American mussel fauna disappearing in the last 100 years, a rate of extinction comparable to estimated faunal losses in tropical rainforests (Ricciardi and Rasmussen 1 The Unit is supported jointly by the U.S. Geological Survey, Virginia Department of Game and Inland Fisheries, Wildlife Management Institute, and Virginia Polytechnic Institute and State University. * Corresponding author: [email protected] Received September 11, 2004; accepted February 15, 2005 Published online June 17, 2005 1999). Most of the endangerment is caused by habitat loss or destruction due to impoundment, sedimentation, water pollution, dredging, and other anthropogenic factors that affect the natural structure and function of free-flowing rivers (Neves et al. 1997; Neves 1999). Without immediate efforts to recover federally protected species in U.S. watersheds, the extinction of additional species is likely. To address the threat of future species losses, biologists at the Freshwater Mollusk Conservation Center at Virginia Polytechnic Institute and State University (Virginia Tech) in Blacksburg, Virginia, have developed techniques to propagate and culture endangered freshwater mussels for release of juveniles into rivers of the Tennessee Riv-