On October 19th, 2002 the NCKWS was treated to a tour of the North Carolina State University's Recirculating Aquaculture Research and Demonstration Facility (aka the Lake Wheeler Road Fish Barn) by lab director and tour guide, Dennis Delong. The tour was attended by several NCKWS officers, members and family.

As Dennis explained, the main culture tanks are 15,000 gallons each, with two of them connected to a common filtration system to make a 30,000 gallon system. The facility has two of those identical systems for the final growout phase.

All systems are designed for a maximum loading of 0.66 pounds of fish per gallon of water. Loading is based upon the amount of feed that must be fed to a given biomass of fish. For the main tanks, 0.66 pounds per gallon X 15,000 gallons = 9,900 pounds of fish. With an average weight at harvest of about 1.25 pounds per fish, 9,900 pounds of fish is about 7,000 to 8,000 fish. The facility staff needs to feed those fish about 2 percent of their weight, or about 200 pounds per day. The filters and flow rates are sized to handle that amount of feed input to get good growth rates.

The keys, Dennis explained, are continuous and throrough filtration and lots of dissolved oxygen. The oxygen demands are so high that the lab uses liquid oxygen and infuses it into the water during the filtration cycle. Large buried biofilters are used to colonize nitrifying bacteria. A first stage particulant filter uses a natural vortex to separate large solids. The remaining water passes through a high density (40 micron) rotating drum screen filter solids separator that features an automatic screen cleaner. The remainder passes through the 15 feet deep external biofilters before being infused with oxygen and returned to the storage tanks.

It was an amazing glimpse into what is necessary for higher density koi ponds and gave quite a few of us some ideas for filtration improvements. Thanks to NCSU and Dennis Delong for conducting our tour and to Dr. Greg Lewbart for extending NCKWS the invitation to tour.

Oxygen Supersaturation: Fact or Fiction After the tour, Dan Phillips followed up with Dennis with some detailed questions about supersaturation of oxygen and the potential for harm to fish. Dan had Dennis review a popular koi discussion board with commentary on this topic and solicited Dennis' views. The following is a transcript:

With regard to the discussion on supersaturation at Supersaturation and its potential harmful effects, it seems like some of the participants are quite passionate about their ideas and their expertise... For ponds with diffused aeration, it is very difficult to supersaturate the water, unless phytoplankton is present. Nitrogen is usually the biggest culprit in gas bubble disease and is generally caused by introducing air into a pressurized flow stream where it dissolves and then comes out of solution when pressure is decreased. The fish get the bends...just like divers. If there is sufficient diffused aeration of the pond water, excess gas is driven off and supersaturation does not occur.

At the fish barn, we can supersaturate the water returning to the tanks to about 300 percent saturation--with oxygen, not with nitrogen. The dissolved oxygen level in the water returning to the tanks is about 21 to 23 ppm, but it mixes with the rest of the tank water to give a tank concentration around the saturation level, about 7.8 ppm @ 28 degrees C.