Design and experiment of mass balance-based recirculating aquaculture system for rainbow mussel (Villosa iris)

Abstract: 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. Already, nearly 35 of these 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. The reasons of population decline are due to habitat loss and destruction such as impoundment, sedimentation, water pollution, dredging, and other anthropogenic factors that affect the natural structure and function of free-flowing rivers. With the decline of native North American freshwater mussels, the United States has brought the need for facilities in which endangered mussels can be held for purposes of relocation, research, and propagation. Some approaches to the culture of freshwater mussels to improve growth and survival of juveniles and adults included rearing them in cages, ponds, raceways, and tanks in the United States. Recirculating aquaculture systems was thought to be sustainable and was widely used to culture the fish and recently, to rear freshwater mussels. To develop a suitable system for rearing freshwater juvenile mussels, a water-recirculating aquaculture system was designed based on the mass balance at Virginia Tech's Laboratory for Conservation Aquaculture and Aquatic Ecology located on the main campus in Blacksburg. The water-recirculating aquaculture system included a plastic rectangle trough tank (300 cm × 70 cm × 30 cm) that was utilized as the container for substrate and cultured mussels, submerged biofilter, sump, magnetic pump, air delivery system, and automatic micro-algae drip feeder. The recirculating aquaculture system was evaluated as a culture environment for juvenile rainbow mussels. Two-day-old juvenile rainbow mussels were reared in the system for 60 days. Throughout the experiment, water quality parameters were stable and remained within ranges suitable for juvenile survivals. The mean growth rate of the juvenile rainbow mussels was 15.2 μm/d. The best relative growth rate was 32.4%, which was attained from the 40th to 50th days during the study. The survival rate was 54.6% at the end of the study. Growth and survival rates of juvenile rainbow mussels (Villosa iris) were compared with the previous study. The results showed that the recirculating system improved the growth rate compared to the previous study in pond and raceway culture systems. The recirculating aquaculture system could provide a suitable culture environment for freshwater mussels and is easy to replicate. It might be useful to conduct studies of water quality, feeding regimes, and toxicity testing for freshwater mussels.