Design And Experimental Study Of Recirculating Aquaculture System For Rainbow Mussel (Villosa Iris)

North America contains the greatest diversity of freshwater mussels in the world,nearly300species. However, bivalve mollusks of the superfamily Unionacea are themost imperiled group of animals in the United States, with213species (72%) listed asendangered, threatened, or of special concern. Already, approximately35species areconsidered extinct. With the decline of native North American freshwater mussels,United States has brought about the need for facilities in which endangered musselscan be held for purposes of relocation, research, and propagation.I reviewed the status of freshwater mussels in United States, and also culturetechnology of freshwater mussel in the paper. A recirculating aquaculture system forfreshwater Rainbow mussel (Villosa iris) was designed and evaluated in FreshwaterMollusk Conservation Center at Virginia Tech.2days old juvenile rainbow musselwas cultured in the recirculating system for60days. Algal turf scrubber was added inthe system to improve the water quality, growth rate of juvenile rainbow mussels.Growth and survival of juvenile rainbow mussel was compared under three differentspecies of algae. Growth and survival of juvenile rainbow mussel was comparedunder different depth of sediment in the culture tanks. Funding was provided byRestoration of Freshwater Mussel Populations in the Upper Clinch River Watershed，US Fish and Wildlife Service.Virginia Department of Game and Inland Fisheries,Cooperative Endangered Species Conservation Fund. The main results are as follows:1. Design of recirculating aquaculture system for rainbow musselsTo develop a system supporting rapid growth of juvenile freshwater mussels, arecirculating aquaculture system for freshwater rainbow mussel was designed basedon the mass balance in Freshwater Mollusk Conservation Center (FMCC) at Virginia Tech. The RAS included a plastic stock-watering tank utilized as the container forsubstrate and cultured mussels, submerged biofilter（1.2m i.d.×1m）, sump, pump, airdelivery system and automatic micro-algae drip feeder (1L). The mussel culture tankwas made of polyethylene and was300cm long,70cm wide,30cm deep along themidline, and held approximately350L of water at a depth of16-18cm. The amountwater of making up was50L daily. The vertical influent injection piped with orificeswas used in the submerged biofilter, and water flushed out of the biofilter from thecenter bottom drain. Kaldnes K1bio-media (2L) was suspended in the biofilter.22.8goxygen was aerated into the system by the air delivery system. A magnetically-drivenpump drove water flow at the flow rate of1394L/h. A solenoid valves was installed onthe outlet tube of the automatic feeder to control the feeding frequency and feedingamount by a repeat-cycle timer. All valves installed were PVC butterfly valves.2. Evaluation of the recirculating aquaculture system for rainbow musselsThe recirculating aquaculture system was evaluated as culture environment forjuvenile rainbow mussel.2days old juvenile rainbow mussel was reared in the systemfor60days. Throughout the experiment, water quality parameters were stable andremained within ranges suitable for juvenile survivals. Mean growth rate of thejuvenile rainbow mussel16.4μm/d. The relatively best growth rate was32.4%，which attained from the40thto50thdays during the study. The survival rate was54.6%at the end of the study. The recirculating system improved the growth ratecompared the previous study in pond and raceway culture systems.3. Performance of a recirculating aquaculture system utilizing an algal turfscrubber for scaled-up captive rearing of rainbow musselsAn algal turf scrubber (ATS) was installed in the recirculating system andevaluated for its potential to maintain and improve water quality. Growth and survivalrates of juvenile rainbow mussels (Villosa iris) were compared at90days betweensystem units with and without ATS. Results showed ammonia and nitrite levels werelow and not different among treatments. However, systems with ATS exhibited significantly (P<0.05) lower levels of nitrate and phosphate than systems withoutATS. The average survival rates in the systems with and without ATS were96.7%and96.1%, respectively. No statistically significant difference on survival rates(P>0.05) of juvenile mussel reared in systems with or without ATS. Based on theMANOVA, the growth rate of the juvenile mussels was extremely (Ptime×treatment=0.001) different under time×treatment interaction between systems with or withoutATS. Our results show that freshwater mussel culture systems can be scaled up toincrease production and suggest that ATS may help maintain water quality inrecirculating aquaculture systems in long-term culture of freshwater mussels.4. An evaluation of three algal diets for juvenile rainbow mussel in recirculatingsystemThe experiment lasted13weeks was conducted to assess the effects of threedifferent diet treatments on the survival and growth of juvenile rainbow mussel. Thethree macroalgae were Neochloris oleoabundans, Nannochloropsis and Tetraselmissp.as three treatments. Each treatment replicated3times.200rainbow mussels werereared in each system. The results showed that the final length of the juvenile rainbowmussels was significant different among the treatments (P<0.05). The SGR of thejuvenile rainbow mussels fed with Nannochloropsis and Tetraselmis sp. wassignificantly higher than the treatment fed with Neochloris oleoabundans. Nostatistically significant difference on survival rates (P>0.05) of juvenile mussel amongthe treatments. The juvenile rainbow mussel under different diet treatments allmaintained high survival rate (90.3%、91.8%and87.7%, respectively).5. An evaluation of different sediment depths for the culture of juvenile rainbowmussels in recirculating systemTo develop a suitable sediment depth for rearing freshwater juvenile rainbowmussels in the recirculating system, grow and survival rate of juvenile rainbowmussels was evaluated on different depth of sediment for13weeks. There were threetreatments (D1,4-6cm; D,29-11cm; D3, no sediment). Each treatment replicated3times. Approximate155rainbow mussels were reared in each system. The average length was16.7mm. The results showed that no significant difference on finial lengthof juvenile mussel between treatment D1and D2(P>0.05). And the finial length ofjuvenile rainbow mussel in treatment D1and D2were significant greater thantreatment D3(P<0.05). That means it is benefit for the growth of the rainbow musselto add the sediment in the culture tank. The growth rate can be improved by addingthe sediment in the culture tank in the recirculating system. No statistically significantdifference on survival rates (P>0.05) of juvenile mussel between treatment D1and D2.The survival rate of juvenile rainbow mussel reared under no sediment was significantlower than under the treatments (D1and D2) with sediment. The results show thatadding sediment in the culture tanks was really important to rear the freshwaterrainbow mussel in recirculating system.