SRAC Publication No. 3700 VI PR September 2005 Pond Aeration Craig Tucker* Fish, like all animals, must obtain described by the gas transfer surplus, depending on whether oxygen from the environment for equation: the measured concentration is respiration. Oxygen is far less dC/dt = KL(A/V)(Cs –Cm). greater than or less than the satu- available to aquatic organisms ration concentration. than it is to air-breathers, and the In the equation: dissolved oxygen content of water dC/dt =the rate of oxygen transfer The effect of surface area and may limit the activities of fish. between a liquid and a turbulence In most natural waters, the sup- gas; Oxygen moves to and from water ply of oxygen to water (diffusion KL =the liquid-film coefficient; across the air-water interface. So, from the atmosphere and produc- a greater amount of oxygen can A/V =the ratio of the air-water tion from underwater photosyn- enter or leave a given amount of interfacial area to water thesis) exceeds the amount used water when the air-water interfa- volume; in oxygen-consuming processes, cial area is increased. However, and fish seldom have problems Cs =the dissolved oxygen con- even if the water is initially low obtaining enough oxygen to meet centration when water is in oxygen, the thin film of water normal metabolic demands. In saturated with oxygen at the interface of a calm water aquaculture ponds, however, the under the prevailing con- surface quickly becomes satu- biomass of plants, animals and ditions of water tempera- rated with oxygen, which dramat- microbes is much greater than in ture, salinity and atmos- ically slows the rate of oxygen natural waters, so oxygen is pheric pressure; and diffusion into the water. sometimes consumed faster than Cm =the measured dissolved Turbulent mixing restores the sat- it is replenished. oxygen concentration. uration deficit in the surface film Depending on how low the dis- by moving oxygenated water The liquid film coefficient, KL, solved oxygen concentration is away from the surface, increasing incorporates a parameter called and how long it remains low, fish the overall rate of oxygen trans- the surface renewal rate, which is may consume less feed, grow fer. related to turbulence within the more slowly, convert feed less liquid. The effect of prevailing dis- efficiently, be more susceptible to infectious diseases, or suffocate The gas transfer equation looks solved oxygen concentration complicated, but it is actually sim- and die. Aquaculturists avoid Dissolved oxygen moves into or ple to interpret. The equation says these problems by aerating ponds out of water by diffusion. The rate that the rate of oxygen transfer mechanically to supplement nor- of diffusion depends on the differ- between air and water depends mal oxygen supplies. ence in oxygen partial pressures on three factors: the amount of turbulence, the ratio of surface between the liquid and gas phas- Principles of aeration es—the greater the difference, the area to water volume, and how The rate of oxygen movement far the prevailing dissolved oxy- greater the driving force moving between air and water is gen concentration deviates from oxygen from one phase to the the dissolved oxygen concentra- other. The maximum rate of oxy- tion at saturation. This deviation gen transfer into water occurs Mississippi State University. * is called the saturation deficit or when the dissolved oxygen con- centration in water is 0 mg/L, the Under practical aquaculture con- dard oxygen transfer rate (SOTR) point at which the maximum dif- ditions, the culturist cannot mod- is the amount of oxygen added to ference in oxygen partial pressures ify those environmental variables water in 1 hour under a standard between water and air occurs. to increase the partial pressure set of conditions. The units of As dissolved oxygen concentra- differential and improve aerator SOTR are pounds O2/hour, which tions increase from 0 mg/L, the performance. However, measured can be multiplied by 0.45 to oxygen partial pressure difference dissolved oxygen concentration in derive the metric equivalent in between air and water steadily the pond varies diurnally, so the kg O2/hour. Standard aeration effi- decreases up to the point where culturist can control aerator oxy- ciency (SAE) is the standard oxy- the dissolved oxygen concentra- gen transfer rates by selecting gen transfer rate divided by the tion equals the saturation concen- when to begin aerating. This can power requirement in horsepow- tration. At that point, there is no be demonstrated by looking at a er (hp). Units of SAE are pounds difference in oxygen partial pres- couple of extreme examples. O2/hp⋅hour, which can be multi- sure between water and air (this First, if aerators are operated on plied by 0.61 to derive SAE in is, in fact, the definition of “satu- sunny afternoons when water is metric units of kg O2/kW⋅hour. ration”). Because there is no driv- supersaturated, oxygen will be Boyd (1998) thoroughly describes ing force compelling oxygen mole- lost (degassed) from the water. aerator performance testing and cules to leave or enter water, no So, unless the goal is to remove how to interpret and use SOTR oxygen can be added to water no oxygen from the water or simply and SAE values. matter how much effort is made to mix the water, supersaturated Aerators transfer less oxygen to increase turbulence or air- water should not be aerated. under pond conditions than water interfacial area. Second, the rate of oxygen trans- under the standard conditions of When the dissolved oxygen con- fer is greatest when the mea- aerator performance tests, so centration is greater than the sat- sured dissolved oxygen concen- SOTR and SAE values are best uration concentration (the water tration is very low. In fact, oxy- used to compare similar styles of is supersaturated with oxygen), gen-transfer rates can be maxi- aerators as an aid in selecting the oxygen partial pressure in mized by waiting until dissolved equipment to purchase rather water is greater than in air and oxygen concentration falls to 0 than as design criteria for pond oxygen moves from water to air. mg/L before aerating, but this has use. Also, small differences in In other words, aeration causes obvious drawbacks (the fish SOTR and SAE values are not the dissolved oxygen concentra- would be dead by then). On the meaningful because test condi- tion to decrease. This process is other hand, aerating water when tions may vary and affect results. called “degassing.” dissolved oxygen concentrations Boyd and Ahmad (1987) com- are near saturation is wasteful piled SOTR and SAE values for a Implications for aeration because oxygen transfer and aer- variety of aerators used in pond ation efficiency are very low aquaculture. Each of the three factors in the gas- transfer equation has important under those conditions. So there Good SAE values and durability implications for pond aeration. The are important trade-offs between are most important when select- effects of surface area and turbu- biological goals (optimizing aquat- ing aerators for general day-to- lence are obvious. Aerators ic animal health by maintaining day use. On the other hand, high increase the air-water interfacial dissolved oxygen levels above SOTR values and mobility are area by breaking water into fine some critical threshold) and phys- important for aerators used to drops or creating bubbles. Aerators ical constraints (aerator efficiency save fish in distress. Other fac- also create turbulence that renews and oxygen transfer decline as tors such as cost, durability, spe- the surface film and moves oxy- dissolved oxygen concentration cific application and ease of ser- genated water away from the aera- approaches saturation). vice must also be considered tor. Implications of the third fac- Although the oxygen saturation when selecting an aerator. tor—the oxygen partial pressure concentration cannot be manipu- Durability varies widely among difference between air and water— lated to improve oxygen-transfer aerators, and prospective buyers are a bit more complicated. rates of surface aerators, this is should consult the owners of var- not true for deep-water diffuser ious kinds of equipment for The oxygen partial pressure dif- advice and recommendations. ferential can be increased (there- aerators (bubblers) or aerators that by increasing the oxygen transfer use pure oxygen as the gas phase. Those aerators can be very effi- Common types ot aerators rate) by increasing the saturation concentration (Cs), decreasing the cient because they operate under Paddlewheel aerators measured oxygen concentration conditions where the saturation dissolved oxygen concentration is Paddlewheel aerators are the most (Cm), or both. For surface aerators higher than in surface waters. common types used in large that splash or spray water into ponds. Paddlewheels consist of a the air, the saturation dissolved oxygen concentration is set by Aerator performance hub with paddles attached in a staggered arrangement. The aera- prevailing atmospheric pressure, There are two ways of describing tor is powered by a tractor power water temperature and salinity. aerator performance. The stan- take-off (PTO), self-contained diesel range from 2 to 4 feet; paddles are designs. For a given design, oxy- or gas engine, or electric motor. 2 to 10 inches wide and may be gen transfer can be increased by Electric paddlewheel aerators are rectangular, triangular or semicir- increasing paddle depth and hub usually mounted on floats and cular (concave) in cross section. rotation speed. Increased diame- anchored to the pond bank. Paddles are welded to the hub in ter, paddle depth and speed also There are many different designs various spiraled or staggered increase the power required for for PTO-driven paddlewheels arrangements. operation. (Figs. 1 and 2). Gearboxes and Large-diameter paddlewheels Tractor PTO-powered paddle- automobile differentials have been transfer more oxygen than smaller wheels can have high SOTRs— used for gear reduction. Paddle- diameter aerators, and flat pad- 90 pounds O2/hour or more. Thus, wheel diameters (paddle tip to tip) dles are less effective than other they are particularly useful in emergencies. However, tractors develop more power than is applied to the PTO and aerator drive shaft, and considerable energy is lost through the drive train, so PTO-driven paddle- wheels are not particularly ener- gy efficient. But they are more flexible than other aerator designs. Because they are portable, they can be moved from pond to pond as needed and placed anywhere along the bank. The aerator also can be operated in different modes, depending upon needs. For general pond aeration, PTO- driven paddlewheels are usually operated with paddles submerged 3 to 4 inches in the water. Paddle depth can be increased to 5 to 6 inches for greater oxygen transfer, but this increases fuel consump- Figure 1. One of the first tractor PTO-powered paddlewheels. The device was fabricated from a truck rear end with rectangular paddles welded to the tion and produces a stronger wheels. water current, which forces fish to expend more energy (and con- sume more oxygen) when swim- ming behind the aerator. Nevertheless, the increased pad- dle depth may be needed when maximum oxygen transfer is important during acute dissolved oxygen depletions. Depending on their diameter, PTO-driven paddlewheel aerators require 15 to 30 hp to operate at paddle depths of 3 to 6 inches. Tractors with PTO power ratings of 45 to 60 hp are typically used as the power source. Larger trac- tors may be needed to move aera- tors around on farms with steep, eroded pond levees, but large tractors are an inefficient power source because most of the fuel consumed is used to run the engine and power train rather than to turn the paddlewheels. Figure 2. A tractor PTO-powered paddlewheel operated in a catfish pond. A sidewinder paddlewheel is in the background. When used at paddle depths of 3 to 6 inches and driven by a trac- tor with a PTO power rating of 45 to 60 hp, most PTO-driven paddle- wheels perform best when the tractor is operated at about half throttle (1,200 to 1,500 rpm engine speed). If the tractor has a standard 540-rpm PTO shaft and the aerator gear reduction is about 6 to 1, the PTO shaft speed will be about 500 rpm and the paddle- wheel speed 80 to 90 rpm. Tractor PTO-driven paddlewheels also can be operated with paddles almost fully submerged to mix ponds or provide a current of oxy- genated water to fish held at high densities in harvest socks. When used in this manner, the tractor is operated just above idle speed (300 to 400 rpm engine speed) so that the paddlewheel speed is 20 to 30 rpm. Some PTO-driven paddlewheels, Figure 3. A sidewinder paddlewheel showing the orientation of paddles on the called sidewinders (Figs. 3 and 4), hub. use an in-line pinion-and-bullgear system to reduce PTO shaft rota- tion speed. Benefits of sidewinders are that they are durable and pro- duce a current of oxygenated water parallel to the pond bank where stressed fish congregate. Side- winders also are commonly used to produce a current of oxygenated water to sustain fish concentrated in harvest socks. Personnel who operate PTO-dri- ven aerators should be trained in placing and using them properly to ensure safe operation, optimal usage in critical situations, and long life of the equipment. For routine, everyday use—where efficiency is important—most cul- turists prefer paddlewheel aera- Figure 4. A sidewinder paddlewheel operated in a catfish pond. tors powered by electric motors (Figs. 5 and 6). Electric paddle- wheels used on commercial cat- fish farms are usually powered by 10- to 15-hp motors and have hubs 10 to 15 feet long. Electric paddle- wheels are permanently anchored in each pond and individually controlled by switches on the pond bank. On some commercial aerators the paddle depth can be adjusted for optimum energy use and performance of the motor. The motor should draw about 90 percent of the full load amperage rating to provide maximum oxy- Figure 5. A 10-hp electric paddlewheel aerator. gen transfer and extend motor life. Electric paddlewheel design was systematically studied by Ahmad and Boyd (1988), who found that the best design consists of a 3-foot diameter paddlewheel with pad- dles that are triangular (135-degree interior angle) in cross section. Paddles are about 4 to 6 inches wide, with four paddles attached per row and spiraled in a staggered arrangement around the hub. Paddle depth is 4 to 6 inches. Paddlewheel speed should be about 90 rpm. Commercial designs similar to that proposed by Ahmad and Boyd have SAE values of 4.5 to 5.5 pounds O2/hp⋅hour, which is Figure 6. A series of electric paddlewheel aerators in operation. very good for surface aerators. Pump-sprayer aerators Pump-sprayer aerators have pumps that discharge water at high velocity through pipes or manifolds. Pumps may be powered by the PTO of a tractor (Fig. 7) or by an electric motor. Pump-sprayers are simple and require little maintenance. Pump-sprayers have a wide range of effectiveness and efficiency. Those driven by electric motors have SAE values of 1.5 to 3.5 pounds O2/hp⋅hour. Pump-sprayers powered by tractor PTOs have lower SAE values than electric aera- tors, but may have very high SOTR values (up to 160 pounds O2/hour). Aerators with higher SOTR values usually require large tractors (90 PTO hp, or more) or that the PTO be operated at a high speed Figure 7. One of the many types of PTO-powered pump-sprayer aerators. A (up to 1,000 rpm). horizontal pipe with a series of outlets has been welded to the discharge of a centrifugal irrigation pump. The device is connected to a tractor PTO and Vertical pump aerators backed into the pond with only the horizontal pipe above the water. When operated, water is sprayed into the air through the holes in the pipe. A vertical pump aerator consists of a submersible motor with an impeller attached to the output shaft. The motor and impeller are suspended beneath a float, and water is sprayed into the air through an opening in the center of the float (Fig. 8). Vertical pump aerators can be relatively effi- cient—SAE values usually range from 2 to 4 pounds O2/hp⋅hour— but most vertical pump aerators manufactured for aquaculture have relatively small motors (usually less than 1 hp) and do not produce a large area of oxygenated water. This limits their use to ponds of less than 1 acre, where they can be quite effective. Figure 8. Two vertical pump aerators used in a fish-confinement area. Diffusers or bubblers Fine-pore diffusers operated at low 1 hp/acre in some fish culture airflow rates are more efficient, but ponds. In marine shrimp ponds, These systems use blowers or these systems foul (clog) easily and aerators are also used for constant compressors to supply air to dif- must be cleaned often to keep them water circulation, which in many fusers. The diffusers have many working properly. In addition to respects is as important as the small pores that release bubbles these problems, most culturists dis- oxygenation process in the cul- on the pond bottom. Oxygen is like diffused aeration systems ture of this bottom-dwelling ani- transferred as the bubbles rise because the network of supply mal. Aeration practices used on through the water column. lines and diffusers interferes with most commercial catfish farms lie Diffusers for large-scale aeration fish harvest. between these two extremes. are usually discs, plates or tubes constructed of glass-bonded silica, Diffusers that use pure oxygen in The evolution of aeration ceramic, porous plastic, or flexible the gas phase can have high oxy- gen-transfer rates, but operating on catfish farms perforated membranes. Diffusers are customarily arranged in a grid costs are too high for routine aera- Before about 1980, catfish stock- pattern over the bottom of the tion of large ponds. Pure-oxygen ing and feeding rates were low pond, with the number of individ- systems may, however, have and there were few problems ual diffusers determined by the important specialty uses in ponds, with dissolved oxygen, except oxygen transfer rate of the diffuser such as providing oxygen to fish during unusual events such as and the oxygen consumption rate held at high densities in live cars sudden phytoplankton die-offs or in the water. Oxygen transfer or socks during harvest (Torrans et prolonged periods of cloudy increases with smaller bubble size, al., 2003). weather during the summer. As deeper bubble release point, and farmers sought to increase pro- higher oxygen content in the bub- Aeration practices duction by stocking fish at greater bles. Basic aerator design and the types densities and increasing the feed- of aerators used in pond aquacul- ing rates, episodes of critically Diffused aeration is common in low dissolved oxygen concentra- wastewater treatment, where ture have become somewhat stan- dardized. Paddlewheel aerators of tions became more frequent. basins 15 to 30 feet deep can be constructed to optimize oxygen relatively similar design are used In the early stages of intensified transfer. When bubbles are in most large ponds (>1 acre), and production, oxygen problems released in deep water, hydrostatic vertical pump aerators are com- remained relatively rare and cat- pressure from the overlying water monly used in small ponds. fish farmers used existing farm increases the saturation dissolved Although the choice and design of equipment (such as irrigation lift oxygen concentration, so that for aerators have become somewhat pumps) or aerators fabricated in any value of ambient dissolved standardized, the ways aerators farm machine shops. These early oxygen, the saturation deficit is are used vary widely, probably aerators used a readily available increased compared to conditions because there has been little sys- power source—a tractor PTO. at the water surface. Deep water tematic economic evaluation of Tractor-powered aerators could be also creates a long contact time aeration practices in large com- moved around the farm to any between bubble and water, so that mercial ponds. Although many pond that required supplemental more of the oxygen in the bubble aeration experiments have been aeration. Quite often, the first is transferred to the water before conducted in small ponds, it is dif- sign of a problem would be fish the bubble reaches the surface. ficult to relate the results of those struggling to obtain oxygen at the Aeration efficiencies are also high experiments to conditions in large pond surface. Farmers would if very small bubbles are produced ponds because oxygen dynamics, then quickly place an aerator in because they have a higher ratio mixing characteristics, fish behav- the pond and fish would congre- of total surface area to water vol- ior, and other factors vary so much gate in the small area of oxy- ume than large bubbles. Fine-bub- with pond size. Because there have genated water near the aerator. ble diffusers operated in deep been few appropriate aeration As farmers continued to increase water can have very high SAE val- trials, farmers base their aeration their catfish stocking and feeding ues—some over 15 pounds practices on the availability of rates in an effort to grow more O2/hp⋅hour. labor and capital, their individual fish, most ponds needed aeration Despite the potential for high SAE production goals, and the per- on summer nights. Tractors values, diffusers are seldom used ceived effectiveness of various proved too expensive and difficult in aquaculture ponds. In shallow practices. to maintain for everyday use. ponds, diffusers are relatively inef- The variety of aeration practices Also, tractor-powered paddle- ficient because bubbles ascend to used in pond aquaculture is repre- wheels are not particularly effi- the surface too quickly for effec- sented at one extreme by the con- cient because only a portion of tive oxygen transfer. At diffuser tinuous use of intensive aeration the energy from the tractor depths of about 3 to 4 feet, SAE (up to 10 hp/acre) in marine engine is transferred to the aera- values of most diffusers are about shrimp ponds and, at the other tor. Floating paddlewheel aerators 1 to 3 pounds O2/hp⋅hour. extreme, by infrequent, “emer- powered by electric motors were gency aeration” with 0.5 to more efficient, and by the mid- 1980s they had become the most cally low levels has the disadvan- pond. Note, however, that the common type used on catfish tage of routinely exposing fish to duration of aeration varies greatly farms. suboptimal concentrations of dis- among ponds on a given day. solved oxygen. Despite this draw- Some ponds may need no aera- How much to aerate back, this is the most common tion, while others require continu- In commercial catfish ponds, aeration practice in commercial ous aeration throughout the day. aeration is commonly about 1.5 catfish ponds and is the only The length of time aeration is to 2 hp/acre in each pond. For practice that has proved to be used also depends on weather example, two 10-hp electric pad- economically rational. Maintain- conditions. For example, during dlewheel aerators may be used in ing dissolved oxygen concentra- periods of warm, cloudy weather a 10- to 15- acre pond. There is, tion above a critical threshold most ponds may need continuous however, a strong trend in the throughout the pond has not been aeration for several days. catfish industry to increase aera- shown to be economically justifi- Some catfish farmers begin aerat- tion intensity to 2 to 3 hp/acre able using currently available aer- ing all ponds on the farm at some (three 10-hp aerators in a 10- to ation technology. set time early each night rather 15-acre pond). Many farmers also When to aerate than basing aeration on dissolved maintain a few tractor-powered The need to aerate varies season- oxygen levels. This practice aerators (one for every four or ally because water temperature reduces the labor required for fre- five ponds is common) for emer- affects the rates of respiration and quent monitoring, but increases gency situations where high oxy- photosynthesis. Problems with energy costs by starting aeration gen transfer rates and aerator low dissolved oxygen concentra- in some ponds well before it is mobility are more important than tions are rare when water temper- needed. aeration efficiency. ature is consistently below 60 °F Aerator placement Mechanical aeration at 1.5 to (15 °C). Problems are common 2 hp/acre meets only a fraction of when water temperature is above Little research has been conduct- the total oxygen demand of all 80 °F (27 °C). Based on average ed on this aspect of pond aera- organisms in the pond. In a typi- water temperatures, aeration in tion. If water mixing is important, cal 15-acre catfish pond, the total northwest Mississippi catfish aerators should be placed where oxygen consumed in respiration ponds is uncommon from mid- they will enhance pond circula- by fish, plankton and sediment November through February and tion patterns. For example, water during the summer may range frequent from mid-May through circulation in large, rectangular from 100 to more than 200 mid-September. Local climates ponds is optimized by placing pounds of oxygen per hour. Most and unseasonable temperatures paddlewheel aerators off the bank of the oxygen demand is account- will, however, alter the need to near the middle of the long axis ed for by plankton and sediment aerate ponds. of the pond to direct currents respiration rather than by fish. Episodes of low dissolved oxygen across the short axis (Boyd and When operated in water with a concentration usually occur at Watten 1989). This produces two dissolved oxygen concentration of night during the summer. Most or more (depending on how many about 2 mg/L, good paddlewheel catfish farmers manage each pond aerators are used) water circula- aerators transfer about 1.5 to 2.5 individually by measuring the dis- tion cells in the pond. The worst pounds O2/hp⋅hour under field solved oxygen concentration at placement is in a corner, with cur- conditions. Thus, an energy input intervals throughout the night and rents directed diagonally across of 40 to 130 hp (about 2.5 to 8.5 aerating when it falls below a the pond. When several aerators hp/acre) would be required to level considered critical by the are placed in a pond, they can be meet the total respiratory individual farmer (usually 3 to 5 located where the current of each demands of fish, plankton and mg/L). Oxygen is measured manu- aerator enhances the flow pro- sediment and maintain dissolved ally (see SRAC publication 4601) duced by the others aerators. For oxygen concentrations of 2 mg/L. or, far less commonly, with con- example, an aerator can be placed Clearly, mechanical aeration at 1 tinuous monitoring systems in in each corner of the pond to to 2 hp/acre will not improve the each pond. Aeration continues direct currents parallel to the dissolved oxygen concentration in until past dawn when measure- banks in the same clockwise or the entire pond, but is used only ments of dissolved oxygen indi- counterclockwise direction. One to provide a small refuge of aer- cate that phytoplankton photosyn- drawback to this arrangement is ated water near the aerator. thesis is producing oxygen. that aerator currents tend to erode When dissolved oxygen concen- the pond bottom around the pond Commercial catfish ponds aerated margins and deposit the eroded trations are low, fish congregate on this “as-needed” basis require in that area and remain there material in the middle of the 500 to 1,000 hours of supplemen- pond. The resulting central until oxygen conditions improve tal aeration cumulatively during throughout the pond. mound of loose sediment can the summer growing season. This make it difficult to harvest the The practice of aerating only a corresponds to an average of aquaculture crop by seining. Also, portion of the pond and only about 3 to 6 hours per day per running electrical cables to the when concentrations fall to criti- corners of every pond on a large gen-stressed fish have congregat- Busch, R. L., C. S. Tucker, J. A. farm will be expensive. ed. For example, when the dis- Steeby and J. E. Reames. 1984. Water mixing is not the primary solved oxygen concentration varies An evaluation of three paddle- goal of using aerators in catfish from one end of the pond to the wheel aerators used for emer- ponds, so optimizing water circu- other, most fish will be in the end gency aeration of channel cat- lation patterns is not the most where the concentration is highest fish ponds. Aquacultural important consideration in aerator and the aerator should be placed Engineering 3:59–69. placement. Catfish become condi- at that end. If a portable aerator is Moore, J. M. and C. E. Boyd. tioned to moving near the aerator used to supplement an existing 1992. Design of small paddle- when dissolved oxygen concentra- aerator or to replace a malfunc- wheel aerators. Aquacultural tions are low, and permanently tioning permanent aerator, it Engineering 11:55–69. installed electric aerators should should be placed near the other aerator so that fish are not forced Petrille, J. and C. E. Boyd. 1984. be located mainly for the conve- Comparisons of oxygen- nience of the farmer. Aerators to swim a long distance to find the new aerator. transfer rates and water- should be placed near a graveled, circulating capabilities of all-weather road for easy access during operation and mainte- References and emergency aerators for fish ponds. Aquaculture nance. They also should be near additional reading 37:377–386. the main power source to reduce Ahmad, T. and C. E. Boyd. 1988. the length of power lines. Torrans, E. L., C. D. Hogue, Jr. Design and performance of and S. Pilkinton. 2003. The If more than one permanent aera- paddle wheel aerators. Aqua- sock-saver: A small trailer for tor is to be installed in each pond, cultural Engineering 7:39–62. providing liquid oxygen to many farmers prefer to install Boyd, C. E. 1998. Pond water aera- remote sites on commercial them near each other (all in one tion systems. Aquacultural channel catfish farms. North end of the pond, for example) Engineering 18:9-40. American Journal of rather than to space them widely Aquaculture 65:260–265. along the pond bank. If several Boyd, C. E. and T. Ahmad. 1987. aerators are located far apart and Evaluation of Aerators for Tucker, C. S. and J. A. Hargreaves. one of them fails at a critical Channel Catfish Farming. 2004. Water quality manage- time, fish will be forced to swim Alabama Agricultural ment. Pages 215-278 in C. S. a long distance through oxygen- Experiment Station Bulletin Tucker and J. A. Hargreaves deficient waters to find a haven No. 584, Auburn University, (editors). Biology and Culture near the remaining aerators. Alabama. of Channel Catfish. Elsevier, Putting all the aerators in one end Boyd, C. E. and C. S Tucker. 1998. Amsterdam, The Netherlands. of the pond also reduces the cost Pond Aquaculture Water Tucker, C. S. and E. H. Robinson. of the electrical supply and makes Quality Management. Kluwer 1990. Channel Catfish routine maintenance easier. Academic Publishers, Norwell, Farming Handbook. Van Portable aerators, such as tractor Massachusetts. Nostrand Rei nhold, PTO-driven paddlewheels, should Boyd, C. E. and B. J. Watten. 1989. New York, New York. either be placed in the same loca- Aeration systems in aquacul- tion each time they are used so ture. Reviews in Aquatic that fish become accustomed to Sciences 1:425–472. the location or placed where oxy- SRAC fact sheets are reviewed annually by the Publications, Videos and Computer Software Steering Committee. Fact sheets are revised as new knowledge becomes available. Fact sheets that have not been revised are considered to reflect the current state of knowledge. The work reported in this publication was supported in part by the Southern Regional Aquaculture Center through Grant No. 2003-38500-12997 from the United States Department of Agriculture, Cooperative State Research, Education, and Extension Service.