OXYGEN DEPLETION IN A HIGH INTENSITY HYBRID CATFISH POND AFTER A POWER OUTAGE: HOW MUCH TIME IS TIME ENOUGH?  

A 0.04 ha clay-bottomed catfish pond accumulated biomass over 165 days due to periodic manual addition of biomass and growth from feeding. Due to the small size of the pond and the large biomass in the pond, paddlewheels were turned off during feeding to prevent feed moving into the grass before it could be eaten. Likewise, fish were fed slowly to prevent feed loss and feedings could extend beyond 30 minutes. This simulated a pond experiencing oxygen depletion due to a power outage.

Simulations occurred from standing crop levels of 19320 kg/ha to 128656 kg/ha.  Readings began at time 0, immediately after paddlewheels were turned off and recorded every minute until feeding ceased. Paddlewheels were turned back on and readings continued every minute until Time 0 DO was regained. DO was not allowed to drop below 3.0 mg/l. This reveals the amount of time needed to deplete the pond to a low, but safe level. Times varied depending upon starting DO. An example of the process is shown in the graph above. The table below shows the time needed drop from a DO of 6 to 3 under different biomass rates.

This suggests that while there is little time to react to loss of aeration, there may be more than previously thought, depending on the DO at Time 0 and pond temperature.