WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2014 11 TOP, FIGURE 1. The original drawing of the Partitioned Polyculture System as it appeared in the 1984 issue of Aquafarming, the University of Arkansas Cooperative Extension Service newsletter. BOTTOM, FIGURE 2. Raceways at Edgar Farmer and Sons fish farm, in Dumas, Arkansas, in 1986. Water from an 8-ha “header” pond flowed through the raceways and discharged into a series of two linked ponds. Water was then lifted 3 m using large pumps into a series of ponds that eventually flowed by gravity back into the “header” pond. catfish, blue catfish Ictalurus furcatus, and tilapia (Oreochromis niloticus and O. mossambicus) in a raceway system supplied with geothermal water from artesian wells (Losordo et al. 2004). Fish Breeders of Idaho continues to produce warmwater fish in this facility. The Farmers built their raceway system in 1986 as a means of better controlling production (Fig. 2). Kelly Farmer summarized his motivation by saying, “A pond has control of you. I wanted to manage growout better” (Mattei 1984). The system consisted of 40 raceways (8 parallel raceway systems, each with 5 raceways in a series) provided with gravityflow water from an 8-ha “header” pond. Raceways discharged effluent into a large pond and water flowed into a second large pond before being lifted 3 meters into the highestelevation pond on the farm by high-volume (83 m3/min) pumps powered by two diesel engines. The engines used 42 L/min of fuel, but diesel fuel cost only $0.079/L when the system was built. Water then flowed through three other ponds through culverts before being pumped to the header pond. The seven ponds tied into the raceway system totaled 44 ha. The raceway system produced about 220,000 kg of channel catfish annually. A variety of other species, including bighead carp, silver carp, and paddlefish Polyodon spathula, were grown in the system’s large reservoir ponds. Several ponds were also stocked with channel catfish and produced an additional 122 t annually, for a total annual net catfish production of approximately 7.7 t/ha for the entire system. In contrast to Leo Ray’s geothermal water supply, water temperatures in the Arkansas pond-raceway systems varied greatly throughout the year, from more than 30°C in summer to less than 10°C in winter. Channel catfish grew little, if at all, for several months during winter and cold temperatures predisposed fish to infectious diseases. As such, catfish could not be overwintered in raceways without large losses and could not be stocked in raceways for growout before mid-May. However, the concept showed promise because fish grew quickly—100-g fish stocked in mid-May reached marketsize in one growing season. Dick Pratt and his son Jon built a similar system of raceways and linked ponds in 1988 at Beouf River Fish Farm, Eudora, Arkansas. The Pratt’s system consisted of 108 raceways (36 parallel series of 3 raceways in a series) linked to seven ponds totaling 55 ha. Water flowed through the system at 115 m3/min. As in the Farmers’ system, channel catfish were grown using manufactured feed in raceways and blue tilapia O. aureus, paddlefish, silver carp, or bighead carp were grown in ponds receiving catfish wastes and with abundant natural foods. The Pratt system operated as described only for a few years, suffering some of the same problems encountered by Kelly and Edgar Farmer. Annual net catfish production from raceways was about 320 t, which, when divided by the pond area used in the system, is roughly the same achieved in well-managed traditional ponds at that time (5-6 t/ha). Although Arkansas farmers were pioneers in partitioned pond aquaculture, neither of the two linked pond-raceway systems remains in operation. Frequent disease outbreaks and growing-season limitations related to lack of temperature control contributed to poor profitability. But the primary economic limitation was caused by the flat topography of the Mississippi River floodplain where those farms were located. Achieving gravity flow through the system of linked ponds and raceways required large volumes of water to be pumped against considerable hydraulic head (~3 m). The concept made sense in an era of low energy costs, but when faced with rapidly increasing fuel costs, the systems were abandoned. The relatively high hydraulic head was a common feature of those early systems. This limitation can be contrasted with Leo Ray’s hillside raceways supplied with geothermal artesian water (no head considerations) and the partitioned aquaculture system and its derivative, the splitpond, where water is cycled through the system against very low hydraulic head. (CONTINUED ON PAGE 12)
RkJQdWJsaXNoZXIy MjExNDY=