SPLIT POND DESIGN AND MANAGEMENT FOR CATFISH FARMING

Split ponds are constructed by dividing an existing catfish pond into two unequal basins with an earthen levee. Fish are confined in the smaller basin (usually about 15-20% of total water area) while the larger basin serves as a waste-treatment lagoon. A high-volume pump circulates water between the lagoon and fish-holding basin during daylight and aerators maintain adequate dissolved oxygen in the fish-holding basin at night. Split ponds are easy to manage and allow the genetic potential of fish to be expressed by maintaining favorable environmental conditions for growth.

Practical experience indicates that the fish-holding basin should not be larger than approximately 2 acres. Oxygen management in larger basins is difficult and fish biomass may become so great that problems are encountered with harvest and marketing. Accordingly, ponds larger than 8 to 10 acres should not be used as starting points for construction.

The original split pond design was based on overcoming limitations associated with dissolved oxygen availability. Approximate aeration requirements are easy to calculate from target fish biomass and aerator oxygen transfer rates. Aeration effectiveness is enhanced in split ponds compared with traditional ponds because fish are confined to a relatively small water volume. In that small water volume, fish become the primary oxygen-consuming component rather than plankton and sediment as in traditional ponds. The amount of aeration required to meet the total oxygen demand in the fish basin of split ponds is about half that needed in traditional ponds.

Optimum daytime pumping rate has been more difficult to quantify than aeration requirement. Pumping rate in the original design was estimated by oxygen mass balance at approximately 1,200 gallons per minute (gpm) per 10,000 pounds of final fish biomass. Pumping rates in most commercial systems are less than 700 gpm per 10,000 pounds of fish. Low pumping rates cause chronically low daytime dissolved oxygen concentration near the end of the cropping cycle, which reduces fish growth rate for part of the production cycle.

In practice, fish production in split ponds is first limited by growing season length and second by practical limitations on pump size. At high fish standing crops (>20,000 pounds/acre), the required pumping rate becomes impractical and cost-prohibitive.