WWW.WAS.ORG • WORLD AQUACULTURE • DECEMBER 2012 63 (CONTINUED ON PAGE 62) of DO analysis was not user friendly. When I first arrived at Auburn University in 1964, someone had constructed an electrical DO meter based on instructions provided by Sneed and Dupree (1962); it was a delicate device unsuitable for intensive use. Fortunately water analysis kits for DO and factory-produced DO meters became available in the mid-1960s. Commercialization of the affordable, polarographic DO meter was the keystone for progress in pond water quality management. Knowing the DO concentration, however, is of dubious value unless influence can be exerted on its concentration. In the early days of catfish farming, the usual recommendation was to limit feed input to 35 kg/ha per day to avoid DO concentration less than 3 mg/L (Grizzell et al. 1975). Limiting feeding rate to this amount, however, did not assure that low DO concentration would not occasionally occur. When DO concentration was considered too low, farmers often pumped oxygenated water from another water body into the pond or, if this intervention was not possible, they would place a pump in the pond with low DO concentration and discharge water into the air in an attempt to oxygenate it (Grizzell et al. 1975). Another option was to drive a boat with an outboard motor over the pond surface to agitate water and increase oxygenation. In order to enhance the availability of oxygen at low concentration to fish, lime sometimes was applied to remove carbon dioxide that can interfere with oxygen absorption. From the standpoint of the fish, these methods only prolonged the agony of DO-related stress. Another popular treatment for low DO concentration was to apply potassium permanganate that was supposed to oxidize organic matter and to react chemically to provide molecular oxygen (Lay 1971). I saw a pond to which so much potassium permanganate had been applied that fish dying from low DO concentration had permanganate stains on their bellies. One of my early graduate students found potassium permanganate to be counterproductive for alleviating low DO concentration in ponds (Tucker and Boyd 1977). This work was not received well by researchers or by extension specialists who had been recommending the treatment widely. I was thoroughly admonished by several colleagues for allowing my student to do the study — but mainly for questioning the status quo. We realized that the findings were having an impact upon receiving a letter from the president of the company that manufactured potassium permanganate, complaining about our flawed conclusions harming sales. A manufacturer of fountains for ornamental purposes designed a vertical-pump aerator (2 hp) for catfish ponds. The sales pitch was that aerators would increase DO concentration, which in turn would equate to more fish production. Single, 2-hp units typically were installed in ponds of 4 to 8 ha. Fish stocking rates were increased in ponds with aerators, but the result was a greater number of fish to be stressed by low DO concentration. This phenomenon was the “mother of invention” of the tractor-powered, paddlewheel aerator that was used in low DO emergencies. There are several claims as to the inventor of this aerator, but it apparently was a farmer in Alabama. The first commercially-available units (Fig. 1) apparently were made by the Clark Livingston Machine Shop in Greensboro, Alabama. This aerator could increase DO concentration quickly and drive DO-enriched water throughout a pond (Boyd and Tucker 1979). This machine caught on very quickly, and the vertical pump aerators were junked — I remember seeing piles of these aerators at some farms. Because of the bad experience with vertical-pump aerators, catfish farmers have since shown little interest in small, electric aerators. New tractors were expensive, so catfish farmers purchased used tractors to power emergency aerators. The catfish industry expanded rapidly and soon it was difficult to find used tractors. Farmers decided to modify tractor-powered, paddlewheel aerators to operate on electricity and to fabricate other types of electrical aerators. Between farmers and local machine shops, many different types of aerators were conceived. Aerators are simple machines, so almost anyone with a cutting torch, welding machine, and a little imagination could offer a “better” device. Whenever I questioned the effectiveness of an aerator, it was as if I had told the fabricator that his child was ugly. Some of these devices would have been the envy of both Darius Green (from Trobridge’s poem — Darius Green and His Flying Machine) and Rube Goldberg. I have a set of slides of early catfish pond aerators that is reminiscent of the comical film clips about man’s early attempts at flight. For several years in the late 1970s and early 1980s, there were phone calls almost on a daily basis requesting information on fabricating aerators. Not being an engineer or even mechanically inclined, I told the callers to contact an agricultural engineer. Finally, out of desperation, a project on mechanical aerators was started. Information on how to conduct aerator performance tests was obtained from two wastewater engineers at Auburn University. The “home-made” aerators did not perform nearly as well as commercially-available aerators used in wastewater treatment. Unfortunately, aerators for wastewater were too expensive to use in aquaculture. Of the small electric aerators made specifically for aquaculture, the Taiwanese paddlewheel aerator seemed most applicable to catfish ponds. This aerator was so small that US farmers viewed it as a toy; it was of poor construction and not very efficient. The paddlewheel principle, however, appeared relevant for application to catfish pond aeration. Through consultations with a retired electrical engineering professor, a retired mechanical engineer from a company that made bearings, pulleys, and sprockets, and a machinist who specialized in prototypes, a modular apparatus was devised that would allow different types, numbers, and configurations of paddles to be placed on a shaft and operated at different speeds and paddle tip submergence depths. Moreover, this device was designed to allow measurement of power input to the aerator shaft with a torque sensor. Hundreds of performance tests were conducted using many combinations of paddles and operating parameters, and a design and optimum operating parameters for an efficient paddlewheel resulted (Ahmad and Boyd 1988), but we never actually built an aerator. Some early aerators would have been the envy of both Darius Green (from Trobridge’s poem — Darius Green and His Flying Machine) and Rube Goldberg. Photographs of early catfish pond aerators are reminiscent of comical film clips about man’s early attempts at flight.
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