NC State University / College of Veterinary Medicine
overall systemWe constructed two identical recirculating systems for propagation experiments, each with eighteen 2.5 gal tanks, five 4.5 gal tanks, six 15 gal tanks (29 total tanks in each system), an 85 gal reservoir and a 40 gal biofilter.  For long-term durability in our wet environment, shelving supports and decking are made completely of fiberglass and held together by stainless steel nuts and bolts. 
Accessing tanksA elevated center platform connects the two systems and is used to access the top two levels of the system.
under platformThe biofilters for each system are housed underneath the center platform.
filterThe biofilter is filled with various types of bio-media that serve as surface area for colonization by nitrifying bacteria.  The filter is designed to maximize flow through the filter media.  Three large airstones inserted at the base of the filter provide adequate aeration for nitrification to take place.
reservoirWater flows from the biofilter to the reservoir where it can then be redistributed throughout the system again.  Additional biomedia in the reservoir supplements our ability to filter out harmful ammonia.  
Bottom draw
Water level in each tank is controlled with a double standpipe designed to draw water off the bottom.   This keeps solid waste separate from the fish and also allows us to collect juveniles without having to siphon each tank.
Directional FlowThe dark, round tanks are ideal for reducing stress in fish.  Inflow can be directed to create circular flow within the tank.  This not only benefits fish species that prefer flowing water but also serves to draw sloughed glochidia and transformed juvenile mussels to the center of the tank where they are drawn up by the standpipe.
Baskets for each tankFlow from each tank is collected in a mesh basket (either 100 or 200 um).  This collects solid waste for easy cleaning as well as juvenile mussels.
 lidsWeighted lids on the top of each tank prevent fish from jumping out.
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