66 SEPTEMBER 2017 • WORLD AQUACULTURE • WWW.WAS.ORG production season. In one trial, jumbo shrimp (57 g) were produced in the water treatment cell, amounting to about 18 percent of total production. During the night, shrimp congregated near screens in the flowing water. Unlike in catfish split pond management, water was circulated continuously. Nighttime levels of dissolved oxygen in the shrimp ponds, due to conservative stocking and feeding rates, were typically much greater in comparison to the water treatment areas of catfish split ponds, which typically become anaerobic at night. So far, split ponds have underperformed conventional ponds in shrimp survival and production but other advantages of the split pond have become apparent. Only about one-third of the aeration power is required for the split pond versus that required to aerate traditional shrimp ponds. Also, feeding a 0.5- to 1-ha culture pond is much faster than feeding along the periphery of a 2-2.5 ha pond. The small culture pond that is part of a split-pond system can also be fitted with automatic feeders more practically than a large pond. The harvest of a small pond in the split-pond system is much faster and less labor intensive than a large conventional pond. Greene Prairie conserves much of their water at harvest by pumping from a full pond to an empty pond. A split pond built properly can retain water in the treatment pond when the shrimp holding area is drained, thereby requiring much less pumping energy and time to reduce water levels. Construction of split ponds for catfish have 20 percent of the area devoted to culture and 80 percent devoted to water treatment. For shrimp culture, we recommend that the ratio of culture area to treatment area should be doubled (e.g. 40-60) given the benthic feeding behavior of young shrimp. Split ponds offer the possibility of polyculture without mixing species in the same water body. The greatest disadvantages of polyculture in the United States is the additional time and labor required to harvest and separate fish by species for marketing (Tucker et al. 2014). In earlier work, Whitis et al. (2013) experimented with polyculture of striped mullet Mugil cephalus and Pacific white shrimp. In a replicated tank system, shrimp post-larvae and fingerling mullet can coexist without any significant mortality or production issues. Mullet fingerlings need two years to reach market size (1 kg) when grown with shrimp and will develop roe at the end of the second year. In the event of establishment of a commercial mullet hatchery in the United States, striped mullet would be a very viable candidate for shrimp polyculture in split ponds. In the fall of November 2015, rainbow trout were stocked in one of the shrimp split ponds at Greene Prairie Aquafarm. After all shrimp were harvested in the fall of 2015, 8600 rainbow trout weighing 136 g each were stocked in a 1.94-ha split pond at 4433 per total water hectare. All fish were stocked in the 0.4-ha fish holding area, resulting in a density of 21,500 fish per hectare in the fish Circulators used to move water between shrimp holding and waste treatment areas of split-pond systems at Green Prairie Shrimp.
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