Aquaculture Guide Sheet No 1 Swine Barn Conversion

Transcription

1 Aquaculture Guide Sheet No 1 Swine Barn Conversion 2009 for Fish Culture The process for retrofitting unused facilities for aquaculture production has been the focus of recent research conducted at Lincoln University, Jefferson City, MO. Chuck Hicks, Lincoln University Dr. Bob Pierce, University of Missouri 5/28/2009

2 Swine Barn Conversion for Fish Culture The process for retrofitting unused facilities for aquaculture production has been the focus of recent research conducted at Lincoln University, in Jefferson City, MO. Unused swine barn before conversion. Swine barn after conversion. Charles E. Hicks 2 Robert A. Pierce II, PhD Lincoln University Aquaculture Extension University of Missouri 103 ABNR 904 Chestnut St. Columbia, MO Jefferson City, MO 65101

3 Opportunities exist for farmers to convert unused barns into facilities for rearing profitable alternative agricultural products such as raising fish! The key to success is to identify potential markets for these products and make the conversion with as little expense as possible. Introduction Tank culture offers an alternative to traditional pond aquaculture and can be the culture system used in indoor facilities such as an unused barn. These systems are examples of what is commonly referred to as Recirculating Aquaculture Systems (RAS). In many cases equipment or structures already in place in a former hog operation can be converted for use in the RAS. There are opportunities to retrofit equipment that is already in place and reuse water by developing a RAS to produce fish in a cost-effective manner. The conversion can involve a significant investment so it is extremely important to gather as much research-based information as possible and learn about fish culture, water quality, marketing and other aspects of aquaculture to assure success. This guide provides basic information on RAS technology and converting these facilities into a potential aquaculture enterprise so that informed decisions can be made before investing additional time and money. Take the time to develop plans for the enterprise and identify potential markets for your product at the beginning. The goal for any production system is to produce fish in a cost-effective manner. Cost effectiveness depends on many factors: component capital costs, operating costs, and efficient management of the fish culture system. Recirculating Aquaculture Systems (RAS) Recirculating system technology has advanced rapidly in the last 10 to 15 years. The technology allows fish farmers to raise a uniform product while greatly reducing the use of water by treating and reusing the water. By concentrating fish in a small space the labor for handling, harvesting and processing are greatly reduced. Recirculating systems usually utilize tanks for production making them ideal for indoor facilities. Information in this guide has been developed to specifically to utilize or modify existing equipment in the design a functional fish culture system. The set-up costs are expensive; so preliminary planning is critical for successful and profitable production. The mechanical design is relatively simple. Basically, a RAS is set up in a similar manner as an aquarium water is circulated to the tank with a pump, it is then filtered and re-circulated back to the tank. A minimal amount of water is replaced during the circulation process and this is controlled by the amount of water input. Most of the water is recycled several times before being discharged. An RAS system consists of containers to hold the fish, aerators or air blowers to oxygenate the water, solids removal devises, biological filters (bio-filters) to remove debris and fish wastes, air blowers, pumps to move the water, and plumbing equipment. Each of these components is described in more detail below. Existing materials and design features can be converted so that they are reused as RAS 3

4 components. For example, the flush tank can be used as the bio-filter, the rack structures and tender foot material can be used to support the fish tanks, and the waste pit can be used for sediment removal. Waste material is flushed through the pit and removed to the existing lagoon that was established for wastes from the hog operation. The new components that are added include the tanks, valves and piping, a pump, blower, aeration devises and miscellaneous items. Numerous studies have been conducted to investigate the technical aspects of tank culture, component design, and performance (Losordo et al Recirculating aquaculture tank production systems: An overview of critical considerations. SRAC Publication No. 451.; Helfrick, L. A., and G. Libey. Fish farming in recirculating aquaculture systems: RAS. Department of Fisheries and Wildlife Sciences, Virginia Tech University, Blacksburg, VA). Links to these publications can be found in the Appendix of this guide. As you learn more about the various components of the RAS, you will also need to gather information on other facets involved in fish production including: 1. Aquaculture basics, 2. potential fish species, 3. feasibility assessment - existing facility, equipment, and water supply (see minimum requirements below), 4. markets for your product, and 5. a cost/return budget that is based on realistic figures. Each of these topics are briefly described. However, the more information you can gather on each of these topics the greater the likelihood of success with the aquaculture enterprise. First, learn about aquaculture basics and then investigate the species of fish which you want to consider. There are several potential fish species for aquaculture in Missouri that can be produced using the RAS. Warm water fish include sunfish, sunfish hybrids, hybrid striped bass, large-mouth bass and channel catfish. Trout can be raised in cold water when abundant quantities of spring or cold well water are available. Other species can be successfully produced in Missouri ponds, but may not be successful in a RAS. Then, evaluate potential viable markets, determine the feasibility of your existing barn and ensure that an adequate water supply exists. After you have determined your species and verified that your barn is feasible be sure to evaluate whether or not you have the necessary capital to invest in this production system. 4

5 1. Aquaculture Basics An understanding of the basics of aquaculture production is essential for a successful enterprise. It is critical to have a thorough understanding of water chemistry and the biology of the fish species you are considering. These interact together to create a fish culture system that is conducive to producing a healthy fish and one that grows in the time interval to assure a profit. Fish culture systems are dynamic in that a change in one component (such as a water quality parameter) will cause changes in another. Understanding the dynamics of these interactions is essential for successful fish farming. Water Quality Maintaining good water quality is absolutely essential. Poor water quality can reduce growth rates, cause disease, stress the fish and foul the filters. It is critical to understand specific water requirements for the species of fish under consideration and management of the water. Fish have tolerances for varying levels of dissolved oxygen, ammonia-nitrogen, nitrite-nitrogen, nitrate, ph (degree of acidity), alkalinity (a measure of calcium and magnesium carbonate content) and hardness. Each species has a specific preferred range and this must be understood and maintained in the culture system. Additionally, water velocity (flow rate), fish loading (density), feeding rate and turnover all directly influence water quality. These parameters should be monitored and recorded on a regular basis. The filtering system removes suspended solids during recycling. Solids which settle on the bottom are removed by siphoning. Dissolved solids are diluted with the addition of fresh water and biochemically broken down into non-harmful products by the bio-filter. In a RAS, a successful producer will be an effective water quality manager. Similar to other production livestock, the management of waste products is a significant cost of production and operation of the system. With fish, solid wastes, as well as soluble waste, are important considerations. Feeds that are not consumed eventually decompose within the system and produce additional ammonia which is toxic to fish. A key to managing a successful RAS is to use cost-effective water treatment components that efficiently remove waste solids, oxidize ammonia and nitrite-nitrogen, remove carbon dioxide and oxygenates the water before returning it for reuse. Success or failure of these systems is directly related to water management strategies. It is highly recommended to invest in a water quality sampling kit such as a HACH kit (see source at end of document). These kits are easy and produce reliable results for measuring water 5

6 quality parameters. Record each daily and watch for changes which are the first sign that the water needs to be adjusted. Feed Feed is often the highest expense in commercial fish production. Therefore, to realize a profit it is essential to feed the amount necessary for maximum growth while not wasting feed or over feeding. The amount of feed and nutritional requirements for most commercial species has been determined. Typically, feed 3% of the total body weight. Knowing the size and weight of fish in the system allows one to back calculate the amount of feed needed. This is easily accomplished by weighing and measuring a representative sample and extrapolating to the whole population. Feed must be fresh and stored in a dry place to prevent molding. Fish growth is not only dependent on water quality but also dependent on feeding a high-quality diet at rates that prevent waste. Fish can be feed by hand or with automatic feeders (available commercially). Fish Health Monitoring the health status of your crop is the first and most critical defense to preventing a disease outbreak. Many pathogens are frequently found with the fish and do not cause problems. However, when the fish are stressed these organisms can be detrimental. Know your fish! The first sign of fish acting differently or going off feed is a warning. Record any mortality daily. Losing a few fish daily is a sign of a chronic problem compared to having a greatly increasing number of mortalities daily. Disease can be prevented by proactively having a biosecurity plan in place! Develop a working relationship with a trained fish health specialist or veterinarian. This is extremely important because unlike other livestock, fish have very few approved medicaments to treat disease. 2. Species Selection Several species of fish have potential to be produced in these systems. Fish species that are commonly produced in RAS s include sunfish, (including crappie, bluegill), large-mouth bass, hybrid striped bass, yellow perch and tilapia. Many of the sunfish and black bass are native to Missouri and are included on the Missouri Department of Conservation s Approved Aquatic Species List. Raising tilapia or other non-native species requires special permission from the Conservation Department. Refer to the Wildlife Code of Missouri to ensure regulatory compliance. In Missouri, bluegill and hybrid striped bass are excellent species for producing in RAS s. They grow well at water temperatures that can be maintained without water heating equipment and are recognized as having the potential to be marketed as a food fish in the state. Both species will grow well in water maintained at 70 0 F to 78 0 F. Crappie, although difficult to feed train, can be grown at lower temperatures from 60 0 F to 65 0 F. 3. Evaluate the feasibility of your facility. 6

7 Below is a list of the minimum requirements for retrofitting an unused swine facility to aquaculture production. Consider each to determine what existing equipment is available that can be used or easily adapted. 1. A reliable supply of high quality water. Water from a well is the preferred supply. If district water is used residual chlorine is removed by using a charcoal filter. 2. A large sediment pit that empties into a lagoon. The sediment pit is used for the removal of solids, fish waste, excess feed etc. 3. Flush tanks for use as bio-filters (below right). Racks hold the tanks (above left) and a flush tank serves as the biofilter (right). 4. Rack systems used to support the fish rearing tanks (above). 5. Reliable electrical supply complete with a back-up generator which can be operated from a tractor power take-off. An LP or natural gas powered generator with an automatic switching system is the most reliable. 6. A telephone alarm system to notify operator of pump, blower, or other electrical supply problems is desirable. Scales are used to weight the fish. 7

8 4. Establish A Market Determine who will buy your fish and in what form they want their product. The final product could be live fish, dressed fish, filleted fish or fish steaks. Depending on your product, you may need to develop a Hazard Analysis Critical Control Point (HACCP) plan. In Missouri, this course (HACCP) may be taken on line. Many producers sell their fish directly to restaurants, at farmers markets or to seafood distributors. Determine where you will sell your fish and check the local health department regulations. Then, determine how many fish will be sold on each date and ensure meeting the demand. The Missouri Department of Agriculture has an Aquaculture Marketing Specialist who is available to assist in marketing your product. You also need to determine how you will get your product to market. Live fish need to be hauled in aerated water and processed fish need to be kept cold at the proper temperature. 5. Establish a Budget Make a budget based on realistic figures. Sketch a proposed layout to assist determining your needs for the conversion, refer to the before and after examples in figure 1. Go through this process to determine if the project is profitable and to help estimate the market value of your product. Skipping this step could result in a product that is not marketable. Knowing the market value will be critical in setting up your market. Figure 1 Typical Swine Barn before Conversion showing before and after. 8

9 Table 1. Example Budget (costs are illustrative only, reader must verify current costs). System and Production Costs (Simulated Budget) Construction Annual Fixed Costs Total Cost Cost/lb $1,900 $ Piping and fittings $1,200 $ Pump $ $99.00 Bio-Filter Existing Tank Biofill (7 cubic feet) $ $ Regenerative Blower $ $ Nets, tubs, bucket etc. $ $ Building Overhead 0.02 Interest on Investment 0.1 Depreciation on Equipment 0.15 Total Fixed Costs $4, Variable Costs Fish $0.35 $ $ Feed 0.35) $ $ Heating/energy $ $ Labor: Management $ $ Interest on Variable Costs $ Total Variable Costs $2, Total All Costs $6, The budget depicted in Table 1 is for a small system producing approximately 1,500 pounds of fish annually. Larger systems would have higher initial capital investment but differences in equipment cost per unit would decrease as scale of the system increased. For example, one tank twice the size of the tank in the budget would not be double the cost. This would be similar for other items as well, especially pumps, blowers, and other equipment. The next two sections provide more in depth information regarding setting up the system and water quality. 9

10 Components in a Recirculating Aquaculture System There are several critical components that make up a RAS necessary for successful production of fish. A general description for each of these components and how they function is provided below. The bio-filter is the nucleus of a RAS and functions to remove toxic dissolved ammonia. Bio-filter The capacity of the bio-filter is the limiting factor for fish loading (size and numbers of fish to put into a RAS), feeding rates and water flow rate. Once any of these three factors is greater than what the biofilter can handle the system becomes overloaded and unhealthy for the fish. At this point the water needs to be treated, diluted, siphoned or otherwise managed to maintain good water quality. The biofilter is a container which water flows through and holds substrate to which nitrifying bacteria live. Ammonia is produced as waste from fish metabolism; it is the primary dissolved waste in a recycle system. Ammonia is very toxic to fish and must be removed from the water. There are two types of nitrifying bacteria: Nitrosomonas, and Nitrobacter. Nitrosomonas oxidizes the ammonia to nitrite and then Nitrobacter converts the harmful nitrites to harmless nitrates. Nitrates at normal levels are nontoxic to fish. The bio-filter must be designed to hold enough bio-mass of bacteria to eliminate the production of ammonia. The capacity of the bio-filter is determined by the surface area of substrate necessary to support the quantity of bacteria needed to denitrify the water. Generally the assumption is that approximately 2.5% of feed becomes total ammonia nitrogen (TAN). Note that ph and temperature affects the TAN. A rule of thumb is that 1 cubic foot of media provides enough substrate to convert ammonia from 1.0 to 1.4 pounds of feed /day/ft 3 of medium. Media can be purchased commercially; several different types are available. Refer to the listing of suppliers at the end of this publication. Most suppliers have technicians on hand to help the producer determine the proper media and how much to use. Sand, rock and shells can also be used. Although not its primary function, the bio-filter also functions to degas water and can aerate the water if it is elevated and provides a drop for the outgoing water. 10

11 Bio-filter Substrate Selecting the bio-filter substrate material is critical to its effectiveness and influences the costs of set-up. Most material is rated by square feet of surface area per cubic foot of material. Costs are different for materials and selecting high surface area per cubic foot will provide the best efficiency. The converted flush tank bio-filters contain a substrate called Bio-Fill that is rated to have 250 square feet of substrate surface per cubic foot of material. The material is relatively inexpensive but has some properties that are not as beneficial as other material. Starting a new bio-filter takes time for the bacteria to build up to a point where there is sufficient quantity to handle a full load of fish. Most systems do not become fully operational for days. It is wise to be cautious during start-up by initiating the bio-filter with a minimum fish load. Often the bio-filter can be jump started by adding a specially prepared bacteria culture. These can be obtained from most aquaculture supply companies. Bio-filter Capacity Design Designing the bio-filter capacity or size is determined by the amount of feed fed daily. Fish loading is dependent upon bio-filter capacity, water flow, tank size and feeding rate. Assume a tank can support no more than 0.5 pounds of fish per gallon (near market size) and assume that the fish are receiving about 2% feed per day. A 100 gallon tank maximum load would be 50 pounds of fish fed 1 pound of feed per day producing about pounds of TAN requiring 1 ft 3 of media. The design criterion has shown that the capacity of feed in the tank is one pound per day. Assuming that smaller fish in the tank are fed at twice the rate of the larger fish the capacity is reduced by ½ ( 25 pounds of 4 inch fish fed 4% of their body weight daily would require 1 pound of feed, 25 lbs. x.04 = 1 pound). This is the design capacity. Aeration Because fish and the decomposition of organic materials both consume oxygen the water must be aerated. Highly efficient regenerative blowers can provide the aeration needed. These are high volume low pressure blowers that provide dissolved oxygen for fish survival and metabolism. The bio-filters need oxygen for the nitrifying oxidizing process. Additionally, the aerators create water movement or flow to allow removal of suspended solids. Regenerative blowers come in many sizes; the appropriate size should be chosen. Figure 4 Manifold Aerator The tanks are aerated by simple manifold aerators (figure 4). The manifold aerator releases dissolved oxygen on one side and is deflected into the water creating a directional flow. The circular direction deposits most of the waste matter in the center where it can more easily be removed. Some of the wastes will go out the centrally located drain. Solids should be removed rapidly to prevent leaching into the water and adversely affecting water quality. When solid wastes accumulate the organic matter begins to decompose which consumes dissolved oxygen that would otherwise be available to the fish. Additionally, debris accumulation provides a reservoir 11

12 for diseases. Uneaten feed will break down into small pieces that will cloud the water and clog the fish gills. Water Flow Water flow rate is dependent upon the total volume of water in the tanks, the replacement water coming in and the capacity of the pumps to move the water. The best management practice is to replace the total volume every 30 minutes. This is referred to as the water turnover. The flow rate directly influences water quality. Water flow rate can be measured by collecting the water coming into the tank during a 6 second interval and multiply that number (measured in gallons) by 10 for gallons/min. The tank volume is known so determine how many minutes it will take to replace the number of gallons in the tank. Visualize the water as a fluid conveyor bringing in dissolved oxygen and removing harmful wastes. The conveyor must move fast enough to supply adequate quantities of dissolved oxygen for fish survival and growth and to remove dissolved and solid wastes. Dissolved wastes, primarily ammonia, are products of protein metabolism and very toxic to fish. Plumbing The fish tank water flows from the bio-filter through PVC pipe that is supported by the fish tanks (figure 2). Because this pipe has no drop the diameter must be large enough to prevent any reduction in water flow. Each tank has a corresponding valve (orange colored) and a vertical inlet pipe that is submerged in the tank. Holes are drilled on the sides of the inlet pipe and are distributed in the same direction as the shield on the aerator. The direction of the flow enhances water movement and removal of wastes. The outlet pipe (PVC) from each tank is normally as large as the main supply line. If more than one individual tank is drained into a common exit pipe then the pipe must be large enough to receive more than one tank when the drain is pulled. Pulling the drain is an easy way to remove wastes which have accumulated in the center of the tank. Figure 2 Typical Conversion Depicting Water and Air Flow Return Line to Biofilter from Sump Air Lines to Tanks Air Line to Biofilter Biofilter Return Lines to Tanks Solids Settling Area Between Headers to be Filled with Filter Media Drain Lines from Tanks Air Diffusers Header with Sliding Gates 12

13 Waste Pit The waste pit functions primarily for settling and removal of solids. A minimum of 20 minutes detention is required to settle most solids out of the system. Greater residual times will enhance removal of solids to the point that will require less frequent flushing for cleaning. A blocking devise in the waste pit pools the water and can increase the residual time. Slats, on the bottom of the blocking devise, direct most of the flow along the bottom of the pit. The slats need to be easily removed for cleaning the waste pit. Air stones or other air supply devises can enhance removal of settled waste material by resuspending wastes before the slats are pulled. Air stones further prevent consumption of dissolved oxygen due to decomposition of organic material. The best case scenario is to have a drain leading to the lagoon at the end of the waste pit (figure 3). Removal of the solids is accomplished by pulling the stand pipe to the lagoon exit. The pit can be cleaned by removing the slats and brushing accumulated debris towards the standpipe. Pull the standpipe and the wastes are transported out to the lagoon. Figure 3 Waste Pit, Solids Settling Configuration Return Line to Biofilter from Sump Air Lines to Tanks and Filter Drain Standpipe Return Line to Tanks Solids Settling Area to be Filled with Filter Media Tank Bypass Note water from the biofilter pit is pumped up and into the biofilter (figure 4). 13

14 Figure 4 Biofilter. Flush Tank Bio-Filter Managing Water Quality in a Recirculating Aquaculture System The most important, yet least understood, aspect of raising fish is an understanding of water quality, especially in recycle systems. Success or failure of a RAS is dependent on knowledge of water chemistry and maintaining various water quality parameters at or above required minimum levels. There are other water quality parameters that are operating in a recycle system; however, the items mentioned below are very important and should be monitored and recorded daily. Oxygen. Fish require dissolved oxygen to sustain body activity and metabolize food. Low oxygen causes stress and does not allow for normal growth. Oxygen is also necessary for the bacteria to convert soluble wastes to non-toxic forms. Oxygen levels below 5.0 ppm can stress fish and reduce food intake and metabolic rate. ph. ph is a measure of the acidic or basic condition of the water. It is related to the concentration of hydrogen (H + ) or hydroxyl (OH - ) ions. ph is especially important in recycle systems because there is a tendency for the water to become more acid. Fish utilize oxygen and give off carbon dioxide (CO 2 ) through respiration. The CO 2 mixes with water to form a weak acid. The conversion of ammonia (NH 4 +) to nitrite (NO 2 ) and nitrate (NO 3 ) together with water form acids. Over time recycle systems become more acid especially in waters that are not buffered well. Buffering refers to the levels of calcium carbonate (CaC0 3 ) in the water and is recognized by the term alkalinity. High alkalinity indicates a good buffering system. ph does not fluctuate widely in waters that are buffered, values between 7 and 8 are adequate for RAS. Alkalinity. As mentioned earlier, alkalinity is a measure of the calcium carbonate concentration in the water. Water with alkalinities of 100 ppm or above have good buffering capacity. Water obtained from wells or other sources in limestone areas, such as Missouri, tend to have high alkalinity. Ammonia. Two types of ammonia exist in an aquaculture system, ionized ammonium (NH 4 + ) and unionized ammonia (NH 3 ). The un-ionized form is toxic and occurs in higher concentrations at higher ph. 14

15 Various fish species have different tolerances to ammonia toxicity, however in general it is a good idea to maintain the levels of un-ionized ammonia below 0.03 ppm. Refer to other guidebooks to use the conversation table using the temperature and ph to get an accurate un-ionized ammonia level. Anyone expecting to be successful in raising fish should obtain an in-expensive oxygen meter and a water quality test kit that measures these basic water quality parameters. A thorough knowledge of operating the kit and interpreting the results are a necessity for success. The meter and test kits are readily available from commercial aquaculture suppliers. Conclusions Converting an operating or abandoned swine facility to commercial aquaculture production can be achieved using the techniques described in this guide. However, raising and producing fish using RAS technology requires skills and knowledge that differs from traditional livestock enterprises. In addition, before any investment is made, it is critical to develop marketing channels for the aquaculture products that you plan to produce in these systems. It is recommended that you start small with a minimum investment to gain initial skills in aquaculture, equipment maintenance, water quality management, and to understand successful methods of marketing aquaculture products. Knowledge of fish culture and of the operation and management of RAS will insure success and potentially lead to a profitable enterprise. Profitability will ultimately depend on skills in keeping costs low and successfully marketing the fish products. Excellent sources of information about aquaculture can be obtained by accessing Aquanic at is an information site sponsored by the North Central Regional Aquaculture Center, Most of the information is available at no cost and are compilations of many years of research. The information is organized so that species descriptions, techniques, systems and other data may be easily found. Many farmers starting in aquaculture find discussing items with other fish farmers to be a great help. A listing of aquaculture sites and fish farmers is available through the Missouri Aquaculture Association at An additional source of excellent information can be obtained from the Missouri Department of Conservation and the Missouri Department of Agriculture. 15

16 Table 1. A List of References about Recycle Aquaculture Systems and Sources for Equipment and Supplies. RAS Publications Recirculating Aquaculture Tank Production Systems: An Overview of Critical Considerations (PDF 143k) - SRAC Publication No. 451 Recirculating Aquaculture Tank Production Systems: Management of Recirculating Systems (PDF 116k) - SRAC Publication No. 452 Recirculating Aquaculture Tank Production Systems: A Review of Component Options (PDF 388k) - SRAC Publication No. 453, revised 1999 Recirculating Aquaculture Tank Production Systems: Integrating Fish and Plant Culture (PDF 7271k) - SRAC Publication No. 454 Pond Recirculating Production Systems (PDF 226k) - SRAC Publication No. 455 The Economics of Recirculating Tank Systems: A Spreadsheet for Individual Analysis (PDF 116k) - SRAC Publication No. 456 Culture of Small Zooplankters for the Feeding of Larval Fish (PDF 129k)- SRAC Publication No. 701 Artemia Production for Marine Larval Fish Culture (PDF 126) - SRAC Publication No. 702 Measuring Dissolved Oxygen Concentration in Aquaculture (PDF 607k) - SRAC Publication No Workshop on Commercial Aquaculture Using Water Recirculating Systems , sponsored by NCRAC, Illinois State University, Illinois-Indiana Sea Grant Program University Publications Comparison of Energy Needed to Heat Greenhouses and Insulated Frame Buildings Used in Aquaculture and (PDF 21k) - University of Florida Principles of Water Recirculation and Filtration in Aquaculture and (PDF 177k) - University of Florida Sanitation Practices for Aquaculture Facilities and (PDF 50k) - University of Florida Basic Principles of Biofiltration and System Design - Southern University at Carbondale Fisheries Bulletin No. 9 Evaluation of Recirculating Aquaculture Systems - University of Minnesota & Minnesota Department of Agriculture, October 1997 Microcontrollers in Recirculating Aquaculture Systems and (PDF 114k) - University of Florida, April 1994 Fish Farming in Recirculating Aquaculture Systems (RAS) - by Louis A. Helfrich and George Libey, Virginia Tech Sources for Equipment and Supplies HACH Company - water sampling kits PO Box 389 Loveland, CO Aquatic Eco-Systems Aquaticeco.com 16