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Updates on Split Pond Catfish Production

Matthew “Rex” Recsetar, Extension Aquaculture Specialist, UAPB

We now have two years of data on commercial catfish production in split ponds.  For anyone not familiar with the term “split pond”; A split pond is basically a hybrid of recirculating and pond aquaculture production systems that utilizes natural processes to provide improved water quality for the fish.  The concept was first pioneered by Craig Tucker at the National Warmwater Aquaculture Center at Mississippi State University.  His split-pond system essentially involved taking an existing catfish pond and splitting it into two sections, where a small section was used for growing fish and the remaining large portion used for biological waste treatment processes.  

During the day, biologically-filtered, oxygenated water from the non-fish section is continually circulated through the fish section via a paddlewheel or pump.  The original design had the fish contained in about 20 percent of the pond area via screen structures where they could efficiently be fed, harvested and aerated at night.  Oxygen monitoring systems turn on water circulators when oxygen is above a set point temperature (ie. 4ppm) in the waste treatment area.  Likewise, paddlewheel aerators are automatically turned on as oxygen levels drop below set points in the fish culture area (typically at night).  By keeping the fish culture area relatively small, farmers are able to allocate aeration specifically to fish, without having to waste it on bacterial and algal respiration as would be the case with a larger pond area.   A picture of two split ponds is below.

So far research verification in Arkansas has collected data on over 25 ponds over the last two years.  All ponds in the study were stocked with hybrid catfish as single-batch crops.  Stocking rates in split ponds have been between 9,000 and 15,000 head per acre when the desired market size was between 1.5 and 2.0 pounds.  We are close to establishing recommended stocking rates and stocker size based on desired yields.  Most split pond systems were fed an average of 200 pounds of feed per acre per day over the course of a growing season.  There were many days where split ponds were fed over 300 pounds per acre and even as high as 500 pounds per acre in a single day!  Annual yield has ranged from 9,000 to over 20,000 pounds per acre with an average of just over 15,000 lb/acre.  Average survival has been just above 82%. Feed conversion ratios have averaged 2.35 and been as low as 1.88.  Water quality, dissolved oxygen and flow rates in these systems were measured weekly and ammonia was rarely present within the systems.  Furthermore, they seemed to provide excellent oxygen management with no algal bloom crashes despite the abundance of algae.

Although initial harvests have been met with some success, they have not come without drawbacks.  Besides a large upfront investment cost, these systems can be costly to repair.  In a few instances we have had paddlewheel shafts break, variable frequency drives (VFDs) burn up (sometimes due to lightening) and wing walls collapse.  Maintenance can also take time.  As water is circulated, various debris can get caught up against the screens and impede water flow.  The debris includes grass clippings and aquatic weeds as well as turtles and other animals that can find themselves unlikely prisoners held by water flow against the screens. Therefore screens must be cleaned periodically (biweekly) either by hand, rake or power washer (seems to work best). Power outages where backup generators were unavailable have proven catastrophic; there was over 50% mortality in one instance.  Where it can take numerous aerators to keep fish alive in the late summer, a single tractor PTO likely will not be enough. Therefore it may be worth investing in a backup generator for split ponds to mitigate the risk of oxygen kills due to power outages at night.  It is also important to do regular maintenance on these systems which includes cleaning probes on the oxygen monitoring buoys, greasing bearings on water circulators and servicing paddlewheel aerators.

If proper steps are taken and recommendations are followed, the split-pond system can be a viable option for catfish production.  Although some of the yields measured fell short of what has been achieved in research ponds, we believe that with increased aeration in some culture areas, production, survival and FCR may yet improve.  Economic analysis of these systems has been ongoing and it is beginning to quantify the trade-offs in investment costs, production costs ($/lb of catfish produced), and profitability of split ponds for catfish production in Arkansas.  Research verification data continue to be collected and we continue to hone in on optimal pond size, stocking densities and circulation rates for split pond systems.

For more detailed data visit: http://aqfi.uaex.edu/extension/verification/pages/catfish_verification/2012_2014/yield_verification_2014.htm

The Importance of Aeration in Split Ponds

Adequate aeration in the fish culture cell of split ponds appears to be the limiting production factor for these systems.  The required horse power of aeration per split pond should be based on the maximum expected biomass and not the size of the fish culture cell.  These 11-acre split ponds pictured below had only 30-hp of aeration which isn't enough to sustain the 200,000 lb of fish expected in each at the end of the growing season, let alone to account for the respiration of the algae and mud in a 2-acre pond on a hot summer night.  Low dissolved oxygen levels over a long period of time can lead to reduced growth and higher feed conversion ratios.

2013 Yield Verification of split ponds and intensive aeration production systems

We are just waiting to harvest a couple more of the intensive aeration ponds and only 4 of the 13 split ponds have been completely harvested so far.  Hopefully this weather gets better so we can finish harvesting these ponds and get out some good data to all you interested folks.

2012 Verification Report and Data Posted

The report and data for split ponds verification is now up on the UAPB extension website. http://www.uaex.edu/aqfi/extension/verification/pages/catfish_verification/2012_2014/yield_verification_2014.htm