Credit: Steve Mims (USA) Source and ownership: Kentucky State University (USA)
Polyculture is the practice of growing two or more fish species with different food habits in the same pond to maximize yield. Polyculture is most sustainable when compatible fish species, having complimentary feeding habits, are stocked so that the ecological niches of the pond ecosystem are effectively utilized and it is not necessary to feed the fish. This practice is accredited to China, originating more than 1000 years ago and has spread throughout Southeast Asia, and into other parts of the world. A variation of the polyculture method incorporates feeding of one species while a secondary species utilizes food naturally produced in the pond. Though using feed is less sustainable, this method allows increased production of fish while limiting additional expenditure to the cost of stockers. Polyculture of paddlefish with channel catfish is a method that fits this description.
Polyculture of paddlefish with channel catfish is a system designed for producing an annual harvest of paddlefish for meat. Caviar production is impractical because the ponds are harvested frequently and the paddlefish must be hand sorted each time. Channel catfish is the primary food fish crop and feeding is required for fast growth at high stocking density. Paddlefish is the secondary crop, stocked at lower density based on the capacity of the pond to produce natural food, which for paddlefish is zooplankton. Feeding of the channel catfish adds nutrients to the pond which increases zooplankton production, enhancing the “carrying capacity” of paddlefish in the system. Tests have shown that producing 500 lbs/acre of paddlefish in combination with catfish produced at 5,000 to 7,000 lbs/acre does not exceed the paddlefish carrying capacity of the pond. Farmers have reported improved water quality (reduced toxic ammonia and nitrite levels) when paddlefish were added to channel catfish ponds formerly used only for channel catfish production. However, paddlefish are less tolerant of low levels of dissolved oxygen than channel catfish so that polyculture of these species requires greater attention to dissolved oxygen management.