30 June 2010 Paddlefish Polyodon spathula polyculture with freshwater shrimp Macrobrachium rosenbergii1 William A. Wurts,2 Steven D. Mims and Richard J. Onders Several Kentucky farmers have adopted low-input shrimp farming over the past few years. While inorganic fertilization is optional, organic fertilization with alfalfa pellets is central to this practice. The use of organic fertilization augments overall pond productivity. Increasing pond productivity ensures that a wide variety of natural food items, including zooplankton, chironomids, nematodes and organisms colonizing detritus are available to shrimp at the beginning of the production season (Wurts 2004). This is especially beneficial for newly stocked juveniles because it provides an ample supply of high nutrient foods, assuring that shrimp have plenty to eat at the outset. Much of the productivity from fertilization is in the form of zooplankton and phytoplankton, which are freely suspended in the water column above the pond bottom. Since the shrimp primarily feed on the bottom of the pond, the phytoplankton serve mostly as food for the zooplankton. Only the plankton that mature, die and fall to the bottom of the pond are available as food for shrimp. The plankton populations represent a large, potential source of natural food that is unused in a fertilized, lowinput shrimp pond. A free-swimming animal that could filter small particles the size of zooplankton from pondwater would be needed to harvest this food source. Fortunately, in Kentucky, we have a native fish that possibly could do the job. The paddlefish or “spoonbill catfish” feeds by swimming through the water with its mouth open, filtering zooplankton with its gill rakers. The 120day growing season for freshwater shrimp production in Kentucky is too short to produce a food-size paddlefish. However, during a shrimp production season, it might be possible to grow a paddlefish fingerling into a paddlefish that is large enough for stocking lakes and reservoirs. So conceivably, polyculture could be used to produce paddlefish stockers with freshwater shrimp using low-input practices. An aquaculture demonstration project was conducted in Kentucky during late spring, summer and early autumn of 2006. Ponds were located in Hopkins and Todd Counties. The study examined the feasibility of growing paddlefish stockers in ponds used for low-input, freshwater shrimp production. Each of three, 0.2 ha shrimp ponds was stocked with 200 juvenile paddlefish (988/ha). Paddlefish were 15-20 cm long and weighed approximately 40 g. Paddlefish were stocked on June 8, 2006. Ponds were fertilized with alflalfa pellets and triple super-phosphate two weeks prior to stocking shrimp. Shrimp were fed a 28 percent protein, pelleted sinking channel catfish feed. No aeration was used in any of the ponds (Wurts 2007). Juvenile paddlefish were allowed to graze the robust zooplankton populations that developed in the fertilized ponds. Ponds were harvested in September 2006. Paddlefish survival ranged from 10-61 percent. Average individual weights and lengths of paddlefish harvested from the three ponds ranged from 261-413 g and 46-51 cm. Paddlefish increased in weight from 653 percent to 1,033 percent in 106-113 days. The Secchi disk measurement in the pond where paddlefish survival was 10 percent was greater than 60 cm at harvest (Table 1). Survival was highest (43 and Paddlefish arm
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