VIEWS: 14 PAGES: 48 POSTED ON: 6/20/2012
THE BEST WAY OUT FOR COMMERCIAL CATFISH
Commercial Catfish Production Feeds and Feeding Nutrient requirements and feeding characteristics of channel catfish have been extensively researched. This research has provided the basis for the formulation of efficient, economical diets and for the development of feeding strategies - both of which have been instrumental in the success of the catfish industry. Photo of feed. Nutrition Catfish farmers are able to feed a nutritionally complete diet that provides required levels of nutrients and energy in a readily digestible form. It is essential to provide a complete diet because catfish can synthesize only a small portion of the required nutrients and the quantity of nutrients from natural food organisms in the pond is relatively small. Forty nutrients have been identified as necessary for the normal metabolic function of channel catfish. Based on current knowledge, a digestible energy to crude protein (DE/P) ratio of 8.5- 10 kcal/gram is adequate for use in commercial catfish feeds. Ratios above this range may lead to increased fat deposition and if the energy ratio is too low, the fish will grow slowly. Catfish feeds contain grain or grain by- products that are rich in starch. In addition to providing an inexpensive energy source, starch helps bind feed ingredients together and increases expansion of extruded feeds so that the feed pellets are water stable and float in the water. A typical catfish feed contains 25 percent or more of digestible carbohydrates. Lipid levels in commercial catfish feeds rarely exceed 5-6 percent. About 3-4 percent of the lipid is inherent in the feed ingredients, with the remaining 1-2 percent being sprayed onto the finished pellets to reduce feed "fines". Both vegetable and animal lipids have been used for pellet coating. Considerable work has been conducted over the last 10 years concerning the level of dietary protein and amino acids needed for cost effective growth. Data from these studies indicate that the dietary protein requirement for various life stages of catfish ranges from about 25-50 percent. Recent studies have indicated that a protein level of 28 percent is adequate for growout when fish are fed to satiation. Catfish feed are generally supplemented with a vitamin premix to meet dietary requirements and to compensate for losses due to feed manufacture and storage. Catfish feeds are also supplemented with phosphorus and a trace mineral premix. However, there is evidence that supplemental trace minerals may not be need in diets using animal proteins. Feeds There are various types of catfish feeds. The type being used at any particular time is a function of size of fish being fed, whether the fish are feeding at the surface or in the water column, and if an antibiotic is incorporated. Catfish fry in hatcheries are fed finely ground meal- or flour-type feeds containing 45-50 percent protein. Fines or crumbles from 28 or 32 percent protein feeds for food fish growout are suitable for fry stocked in nursery ponds until they reach 1-2 inches in length. Larger fingerlings should be fed small floating pellets (1/8 inch diameter) containing 35 percent protein. Advanced fingerlings (5-6 inches) and food fish are generally fed a floating feed of approximately 5/32 - 3/16 inch in diameter containing 28-32 percent protein. Some producers switch to a slow-sinking feed during the winter. Antibiotics are administered to catfish through incorporation in feeds. Depending on the particular antibiotic chosen, the feed may either be floating or sinking. Feeding Despite considerable research, feeding catfish is far from an exact science. It is a highly subjective process that differs among catfish farmers. The variation in feeding practices is a product of numerous factors such as cropping system, fish size, ability to manage water quality, experience of feeding labor, and difficulty in estimating fish inventory. In general, fish should be fed once a day as much feed as they will consume without adversely affecting water quality. However, depending on water quality variables and the health of the fish, it may be advisable to restrict the daily feed allowance or to feed less often. Long-term feed allowance should not exceed 100-125 pounds per acre per day. Most catfish producers feed once a day, 7 days a week during the warmer months. Although feeding twice a day may slightly improve growth of fingerlings, the logistics of multiple feedings on large catfish farms make it impractical. Feed is typically blown onto the surface of the water using mechanical feeders. Feeds should be scattered over as wide an area as possible to provide equal feeding opportunities for as many fish as possible. Feeding with prevailing winds allows the feed to float across the pond and minimizes the amount of feed washing ashore. Overfeeding should be avoided since wasted feed increases production costs. CONSTRUCTION OF THE POND(mobile for pond) The lenght of the pound should not less than 6ft for private consuptins while that of Commercial production should be 12ft 300-700fish and above pending on the amount of fish purchase. Pond Construction Proper design and construction of ponds is critical to the success of a commercial catfish operation. Well-designed ponds, constructed on soil with a proper clay content and adequate water supply, have a useful life of at least 10 years. Pond Types(Earth pond) Three types of ponds are used in catfish farming. The first, called embankment or levee ponds, is the most common type of pond used in channel catfish farming. Embankment ponds are the preferred type for large-scale catfish farming because they can be built in large contiguous tracts, which aids in pond management. Embankment ponds are built on flat land by removing soil from the area that will be the pond bottom and using that soil to form levees or embankments around the pond perimeter. The second type, watershed ponds, are built in hilly areas by damming a small stream. In the long term, the major source of water is runoff from the drainage basin above the dam, although a source of pumped water is desirable to help offset evaporation and seepage during droughts. Watershed ponds represent less than 10 percent of the total pond area devoted to channel catfish farming, but are common in some regions, such as western Alabama. The third pond type is a hybrid between embankment and watershed ponds. These ponds may have two or three sides consisting of embankments (actually low dams) across a relatively small drainage basin. A significant amount of water may be obtained from runoff, but because the catchment area above the pond is relatively small, a source of pumped water also must be available. Hybrid watershed- embankment ponds are built in regions with gently rolling topography, such as the Blackland Prairie of east Mississippi. Pond Morphology The ideal size and depth of catfish ponds has changed in recent years. Fish farmers report that smaller ponds (8 to 10 acres) are easier to manage and feed than larger ponds (18 to 25 acres). Research indicates and producers confirm that deeper ponds (5 to 6 feet average depth) have a longer life expectancy and allow greater water conservation. A bottom slope of 0.2 to 0.3 inches per 100 linear feet along the long axis is recommended for adequate drainage. Interior levees should have a minimum top width of 16 feet to allow vehicle access for management purposes even in wet conditions. Main access levees should have a minimum top width of 20 feet (preferably 25 feet) to accommodate fixed equipment such as wells, generators, and aerators while permitting passage of feed delivery and hauling trucks. These main levees should be graveled for all-weather access. Slope is expressed as the horizontal distance (in feet) that results in a 1-foot change in height. For most soils, an outside levee slope of 3:1 is recommended. Inside slope for commercial ponds typically ranges from 3:1 to 4:1. A single 10-inch diameter drain of heavy gauge, coated metal or PVC pie is adequate to maintain water level and drain a commercial pond. The drain should extend into the pond and past the outside levee toe by at least 5 feet. A perimeter drainage system should be constructed to receive effluents and to prevent water from standing outside levees. Water Quality Water supplies for catfish ponds are usually of good initial quality. However, once the water is used for culture, its quality deteriorates. This deterioration of environmental conditions is ultimately traceable to the use of feed. Despite the use of high quality feeds and careful feeding practices, relatively little of the nutrient value of feed is converted to catfish flesh. The remaining nutrients derived from fish wastes stimulate excessive phytoplankton growth. High rates of phytoplankton metabolism cause pronounced diurnal fluctuations in dissolved oxygen concentrations, dissolved carbon dioxide concentrations, and pH. Such fluctuations cause stress in fish resulting in reduced fish growth rates, poor feed conversion, and reduced resistance to disease. In extreme instances, such as depletion of dissolved oxygen, fish may be unable to adapt and will die. water aeratorLiterally hundreds of environmental variables may affect fish health and survival, but fortunately only a few are important in commercial catfish culture. Because their concentrations may change rapidly, substances affected by biological activity (dissolved oxygen, carbon dioxide, ammonia, and nitrite) are the most important aspects of water quality and its management in catfish pond aquaculture. The development of environment-related off-flavors is another important aspect of water quality management. Off-flavor is unlike the previously listed water quality variables because it does not pose a direct threat to fish health. Rather, it affects the acceptability of fish for processing, which causes delays in harvesting. As such, it increases the cost of production and exposes fish to additional risk of loss to diseases or predators. Important Water Quality Variables Dissolved Oxygen: The supply of dissolved oxygen often becomes limiting to catfish because the combined respiration of fish, phytoplankton, and mud-dwelling organisms exerts a tremendous demand for oxygen. At high phytoplankton biomass levels (which is the typical condition in catfish ponds during summer), oxygen production by algae is insufficient to meet the respiratory demand of the pond community and a daily oxygen deficit develops. If this deficit is not offset by artificial aeration, dissolved oxygen levels will drop very low and fish will die. The key to successful management is early identification of those ponds that may require supplemental mechanical aeration to keep fish alive. Aeration is initiated when dissolved oxygen concentrations fall to a level considered critical (usually around 3 to 4 mg/L). Under current production practices, nearly every catfish pond has dissolved oxygen concentrations less than 2 mg/L at dawn during mid- summer. The duration of low dissolved oxygen concentrations at night usually ranges from 3 to 6 hours/day during mid- summer. Aeration is continued until past dawn when measurements indicate that dissolved oxygen concentrations are increasing as a result of photosynthetic activity. Carbon dioxide: High rates of respiration in ponds with abundant plankton and high densities of fish result in rapid loss of dissolved oxygen and accumulation of carbon dioxide over the nighttime hours during summer months. Dissolved carbon dioxide concentrations of 5 to 10 mg/L are common on summer mornings in catfish ponds and appear to be well tolerated by channel catfish. They can survive in waters containing up to at least 60 mg/L dissolved carbon dioxide provided dissolved oxygen concentrations are high. Higher concentrations may cause death but chronic problems are rare because daytime uptake in photosynthesis normally serves to remove all the carbon dioxide that is produced in overnight respiration. Ammonia: Ammonia is the major nitrogenous waste product excreted by fish. The fact that culture is possible at high feeding rates indicates that transformations and losses of nitrogen act to reduce ammonia concentrations. Additionally, as ammonia begins to accumulate, fish respond with reduced appetite, leading to lower rates of ammonia excretion and reduced ammonia concentrations in the water. As such, there are very few documented cases of acute ammonia intoxication in commercial channel catfish ponds. However, ammonia levels can be used to predict the onset of possible nitrite accumulations. Nitrite: Nitrite is an intermediate product in nitrification, which is a common, bacteria-mediated transformation of ammonia to nitrate in soils and water. Nitrite accumulates to significant levels in ponds only when ammonia concentrations are relatively high and some factor causes the rate of ammonia oxidation to nitrite to exceed the rate of nitrite oxidation to nitrate. Accumulation of nitrite is undesirable because it can be toxic to fish at relatively low concentrations. Nitrite toxicosis caused large losses of catfish in the early days of the industry, but losses are now very rare. An inexpensive and convenient prophylactic treatment using common salt has been developed and monitoring programs are easy to implement. As such, losses to nitrite toxicosis will result only when the farm manager is negligent in instituting the proper management plan Off-flavor When channel catfish are fed a grain- based diet and raised in clean water, they have a characteristic mild flavor. Pond- raised catfish may, however, develop flavors that can be disagreeable. All catfish processing plants sample fish for flavor quality before processing as a quality control measure. Fish are sampled several times over the weeks before a projected harvest date and if any of the samples have undesirable flavors, the fish will not be accepted for processing. Most off-flavors in pond-raised catfish are caused by odorous compounds absorbed by fish from the water. Most off-flavors in pond-raised catfish are caused by naturally occurring organic compounds produced by aquatic bacteria or algae. These microorganisms synthesize and release compounds into the water, where they are absorbed through the gills, skin, or gastrointestinal tract of fish. Managing off-flavors can be divided into two general approaches: purging the compound by moving fish to a "clean" environment or using algicides to kill odorous aquatic bacteria or algae. Many farmers choose a more passive approach, however, and simply wait to harvest fish when they are on-flavor. This approach works to some degree because the composition of pond phytoplankton communities constantly changes. When community composition changes and the odor-producing species disappears, off- flavors produced by aquatic bacteria or algae will be purged from the flesh and flavor will improve. However, it is impossible to predict how long the odor- producing microorganisms will remain in the pond. They may disappear in a week or may persist for months. Production Process A typical production cycle for channel catfish farming begins with spawning of brood fish. Spawning begins in the spring when water temperatures increase to above 70º F. At that time, brood fish held in ponds randomly mate and the fertilized eggs are collected from spawning containers and moved to a hatchery. Eggs hatch after 5 to 8 days of incubation and fry are reared in the hatchery for an additional 4 to 10 days. Fry are then transferred to a nursery pond, fed daily through the summer, and harvested in autumn or winter as fingerlings. Fingerlings are then stocked into foodfish growout ponds, fed daily, and harvested when they reach 1 to 2 pounds. Roughly 18 to 36 months is required to produce a food- sized channel catfish from an egg. Foodfish are harvested year-around to meet the needs of processing plants, so ponds on a given farm usually contain fish at various stages of growout throughout the year. Maintaining Brood stock Aerial photo of catfish pondsChannel catfish brood stock are easy to maintain in pond culture, and spawning efficiency is reasonably good without any special manipulation of environmental conditions or the need for hormone treatments. Although channel catfish may mature at 2 years, they must be at least 3 years old and weigh at least 3 pounds for reliable spawning. Fish 4 to 6 years old, weighing between 4 and 8 pounds are considered prime spawners. Older fish produce fewer eggs per body weight and larger fish may have difficulty entering the containers commonly used as nesting sites. Brood stock are maintained at relatively low standing crops (less than 2,000 pounds/acre) to provide good environmental conditions and minimize suppression of spawning by overcrowding. Brood fish are seined from ponds and inspected every year or two. Large fish, which may be poor spawners, are culled and replaced with smaller, younger brood fish. Periodic inspection of brood fish also provides an opportunity for adjusting the sex ratios within brood populations. Spawning activity will begin in the spring when water temperatures are consistently around 75º F. Spawning occurs over a period of several hours as several layers of adhesive eggs are deposited in spawning containers. Females between 4 and 8 pounds typically lay between 3,000 and 4,000 eggs per pound body weight. Spawning success (percentage of females spawning) ranges from 30 to 80 percent each year, and depends mainly on the condition and age of the female brood fish and water temperatures during the spawning season. Nesting containers are checked every 2 or 3 days for the presence of eggs. The eggs collected from the brood pond are placed in an insulated, aerated container and transported to the hatchery. Hatchery Phase Hatcheries used to produce catfish fry are simple facilities that use flow-through tanks holding about 90 to 100 gallons of water for egg incubation and fry rearing. The most critical factor for a successful hatchery is a dependable supply of high- quality water. Egg hatching tanks are equipped with a series of paddles spaced along the length of the tank to allow wire-mesh baskets to fit between them. One or two egg masses are placed in each basket and the paddles gently rotate through the water to provide water circulation and aeration. The incubation time varies from 5 to 8 days depending upon water temperature. At hatching, the fry (called sac-fry at this point) fall or swim through the wire-mesh basket and school in tight groups. Sac-fry are siphoned into a bucket and transferred to a fry rearing tank. Aeration in fry rearing tanks is provided by surface agitators or by air bubbled through airstones. Initially, sac-fry are not fed because they derive nourishment from the attached yolk sac. Over a 3- to 5-day period after hatching they absorb the yolk sac and turn black. At that time fry (now called swim-up fry) swim to the water surface seeking food. Swim-up fry must be fed 6 to 12 times a day for good survival and growth. Fry are fed nutritionally complete feed for 2 to 7 days before they are transferred to a nursery pond. Fingerling Production Culture practices for fingerling production are relatively standardized across the industry, especially when compared to the wide variety of production strategies used to grow food-sized catfish. Fry grow faster when stocked at lower densities but more space is required to grow larger fingerlings at lower densities. Stocking rate is therefore a compromise between benefits of producing large fingerlings for foodfish growout and the economics of producing more small fingerlings in less space. Fish are fed a manufactured feed and grown to fingerling size (3 to 8 inches long) over a 5 to 10 month period. Fish are either allowed to continue growing in their original nursery ponds or are harvested and transferred to other ponds for growout to stocker-sized fish of 0.1 to 0.25 pounds or to food-sized fish of 1.2 to 2.5 pounds. It is important to fertilize nursery ponds so that they contain abundant natural foods to promote growth until the fry are large enough to switch to manufactured feeds. A finely ground feed should be offered once or twice daily to train fish to accept the feed. As the fish grow, feed particle size is increased. A month or so after stocking, the fish (now called fingerlings) are fed once or twice daily to satiation, using a small floating pellet with 32 to 35 percent crude protein. Because fingerling populations are particularly susceptible to infectious diseases, disease management takes on added importance in this stage of production. Survival of catfish fry to fingerlings varies greatly from pond-to- pond depending on the initial condition of the nursery pond, losses to bird predation, and the incidence of infectious diseases. Average survival from fry stocking to fingerling harvest in excess of 60 percent across all ponds on the farm is considered to be very good. Foodfish Production Cultural practices used for foodfish production differ from farm to farm, and the process of growing a food-sized catfish can take many paths after the fingerling phase. Most farmers divide fish stocks only once between the nursery phase and the foodfish growout phase. In this scheme, fingerlings are harvested and restocked into foodfish ponds at roughly one-tenth to one-twentieth the density of nursery ponds because fish will be ten to twenty times heavier when harvested as foodfish. This one-step production scheme is not as simple as it appears because there are many options for managing foodfish ponds. Another approach to producing food-sized fish is to divide twice between the nursery phase and foodfish growout. The first division produces a medium-sized fish called a "stocker". The second division is made when stockers are harvested and restocked for growout to food size. In this scheme, small fingerlings (2 to 3 inches) are stocked at about 40,000 to 60,000 fish/acre and grown over one season to produce stockers weighing 0.1 to over 0.3 pounds. The stockers are then harvested and moved to foodfish growout ponds. As with the one-step scheme described above, there are several options for foodfish growout using stocker-sized fish. The three fundamental production variables in foodfish growout are cropping system, stocking rate, and size of fingerlings to stock. Farmers use various combinations of these variables and it is impossible to describe a typical management scheme for production of food-sized channel catfish. Farmers have developed and used various production schemes based on experience, personal preference, and perceived productivity and profitability. Cropping system refers to the stocking- harvest-restocking schedule. In the single- batch system, the goal is to have only one year-class of fish in the pond at a given time. Fingerlings are stocked, grown to the desired harvest size, and all fish are harvested before the pond is restocked with new fingerlings to initiate the next cropping cycle. In the multiple-batch system, several different year-classes of fish are present after the first year of production. Initially, a single cohort of fingerlings is stocked. The faster-growing individuals are selectively harvested ("topped") using a large-mesh seine, followed by addition ("under- stocking") of fingerlings to replace the fish that are removed plus any losses incurred during growout. The process of selective harvest and understocking continues for years without draining the pond. Whether ponds are operated as single- batch systems or multiple-batch systems, stocking rate is best defined as the maximum fish density (number per acre) over the production period. Under commercial conditions, stocking rate becomes an approximate goal rather than a precisely managed population variable because it is nearly impossible to know the true inventory of fish in large commercial ponds that are used for several years without draining. There is no consensus on the best stocking rate for commercial production and rates used in the industry range from less than 500 fish/acre to more than 10,000 fish/acre. One explanation for the wide range of stocking rates used by catfish farmers is that production goals, facilities, and resources vary from farm to farm. The size of fingerling to stock is a critical factor in foodfish production, but very little systematic research has been conducted to determine the relationship between fingerling size at stocking and economic returns. Large fingerlings will reach foodfish size faster than small fingerlings, but large fingerlings are expensive because they require more time and space to produce. In addition, large fingerlings can be difficult to obtain because most fingerling producers prefer to stock fry at relatively high densities and move fingerlings to foodfish ponds as soon as possible to avoid risk of loss to infectious diseases and predacious birds. The best size fingerling to stock is therefore a compromise that depends on cropping system, fish stocking density, and fingerling availability. Harvesting Efficient harvesting of channel catfish ponds is important to all phases of channel catfish culture. The techniques currently employed by the industry evolved primarily from Great Lakes haul seine techniques. There has been very little systematic research conducted to improve on existing techniques. Most of the innovations implemented in harvesting fish during the past twenty years have been the result of trial-and-error by fish producers and custom seining crews. Photos of harvesting of catfish.Preparation. Successful harvesting operations require properly constructed ponds. Levees should be wide enough to accommodate large hauling trucks, tractors, and fish loading equipment. Gravel is imperative on main levees where fish will be loaded onto hauling trucks. All other levees should have a good ground cover (or preferably gravel) to permit seining in all types of weather. To ensure the most efficient harvest possible for any given pond, producers must be certain that the production pond contains an adequate amount of fish of harvestable size. To minimize the expense per pound of fish transported to the processing plant, the transport truck needs to be filled to or near capacity. Typically, a producer marketing fish to a large processor will not schedule a harvest until 20,000 to 25,000 pounds of graded fish will be retained in the harvest net. Prior to each food fish harvest, producers must arrange for their fish to be placed on the processing schedule. Producers must first submit fish samples to processing plants to check flavor quality. Once a processor determines that a pond is "on- flavor", the process of scheduling the harvest can begin. There are many factors that complicate scheduling including, processing rights, proximity to plants, availability of fish, and re-occurrence of off-flavor. Basic equipment. The basic requirements are similar for fingerling and food fish harvesting operations. Equipment requirements consist of a commercial harvest seine, a hydraulic seine reel, a flat- bottomed aluminum boat outfitted with an outboard motor and a seine catcher, two tractors, and various live cars for holding and grading fish. An additional tractor equipped with a PTO-driven aerator is recommended to keep water moving in any area where fish are concentrated. In order for a seine to operate properly, the length of the seine should be 1.5 times the widest section of the pond. This allows the seine bottom to conform to the shape of the pond bottom and minimizes the tension on the mud-line. In general, the depth of the seine should be 1.5 times the deepest section of the pond. Most food-fish seines are 9 foot deep for use in delta-style ponds, but may be as much as 12 foot deep for use in deeper watershed-style ponds. The vast majority of fingerling seines in use on commercial farms are 8 foot deep, but some deeper, watershed style ponds require 10 foot deep seines. Basic harvesting operation. While the process of seining a pond is straight- forward, a certain amount of skill and an understanding of basic fish needs are required to land fish successfully with a minimum amount of stress. Even under ideal conditions, a typical seine haul will seldom catch more than two thirds of the fish in a levee style pond. Typically, at least five persons are required to seine a commercial pond. Two persons are required to drive tractors; one to pull the hydraulic seine reel, and the other to pull the other end of the seine. Two more individuals are required to stand on the mudline at the base of the levee as the seine is pulled through the pond. The fifth individual is required to operate the seining boat and monitor the seine as it is pulled through the water, watching for indications that the seine is catching too much mud. Once both ends of the seine are pulled around the corners of the pond, the tractors converge in the vicinity of where the hauling truck will eventually be loaded. This area should be clear of overhead power lines and the pond bottom and water depth should be suitable for containing the fish in a net enclosure, grading, and loading out. Often, producers choose to land fish close to the aerator and the well to help improve water quality in the area where fish will be confined. Technical Advances. Researchers at Mississippi State University have developed a novel design for catfish seines. The original design for the seine was developed in collaboration with the National Marine Fisheries Service Lab in Pascagoula, Mississippi. The seine design incorporates braided polyethylene mesh, a modified mud roller, a larger seine tunnel, and replaces the frame mechanism used to mate the seine to the live car with an industrial- strength zipper system. The braided polyethylene mesh is a good choice for constructing seines and socks. The modified mud roller design eliminates much of the "mudding down" problems associated with older muddy ponds. The zipper system allows the sock to be attached quicker and eliminates the potential for twisting of the seine tunnel. More importantly, it eliminates the "bottleneck" effect of crowding fish through a tunnel and frame, which can significantly reduce the amount of time required to land fish in live cars. A prototype seine was used to harvest catfish from ponds ranging from 4 to 10 acres at the NWAC. Average catch was 20 percent better than with conventional seines and seining time was reduced by 45 percent. Grading Most intensive catfish production operations employ the sock grading method of landing and grading fish. Typically, a tunnel is sewn approximately 100 to 125 feet from the end of the harvest seine. An open-topped net enclosure known as a live car or sock is attached to the harvest seine tunnel. The harvest seine is carefully pulled toward the levee as fish pass through the tunnel and into the sock. Grading catfish with socks depends on mesh size, time, water temperature, water quality, and the general health of the fish. Typically, to achieve the desired level of grading, fish must be held in socks for a minimum of four to six hours. It is common for producers to hold fish overnight in grading socks to encourage removal of small fish. Socks must be staked out properly in order to avoid fish escaping and to encourage grading. A tractor PTO- driven paddlewheel aerator should be placed along the bank to gently pull oxygenated water through the sock. Technical Advances. An adjustable horizontal bar grader for sorting channel catfish has been developed by David Heikes at the University of Arkansas at Pine Bluff and has proven to be a valuable management tool for fingerling production on several commercial farms. A larger version of the in-pond grader design is currently under investigation and shows promise for grading foodfish. Grading foodfish with the in-pond grader involves additional handling and labor, but allows a producer to grade a crop of foodfish immediately after seining. The grader can grade 10,000 pounds of food-sized catfish in 2 to 6 minutes. One series of tests showed that 5 to 11 percent more weight of sub-harvestable size fish can be graded compared to current technology, resulting in a 12.5 percent increase in average weight of fish available for processing. Once the fish have been graded with an in- pond grader, inventory estimates can be obtained from the holding sock. The use on an in-pond grader may be particularly well suited to grading fish in cold weather when sock grading efficiency drops off. Loading Loading channel catfish from holding socks onto transport tanks is typically accomplished with a hydraulic loader outfitted with a boom, lift net, and hanging scale. Two of the most common types of hydraulic loaders are a modified backhoe and a reconditioned logging truck. A long boom is attached to the hydraulic arm of the loader to extend the basket to the live car from the pond bank and lift the fish up to the transport tank. The lift net is suspended from a hanging scale attached to the boom. The fish are weighed before being released into the tank through the trap door in the bottom of the lift net. Transport Channel catfish can withstand the rigors of transport fairly well at all life stages. However, proper procedures are critical during transport of eggs, fry, and fingerlings because damage or stress can result in poor survival. Care should also be taken when "live hauling" food-sized catfish to specialty markets because they are expected to remain alive for extended periods until sold to the final consumer. Food-sized catfish bound for processing plants are transported at higher densities because fish are held only briefly before slaughter. Disease The "low-intensity" management practices used prior to the 1980's generally resulted in good pond water quality and lower overall stress on fish populations. Lower fish densities also meant less efficient transmission of disease organisms. Over the years, stocking and feeding rates steadily increased and producers adopted a multiple-batch cropping system wherein new populations of fingerlings were stocked into ponds with existing populations of larger fish. These production practices lead to the emergence of infectious diseases as the primary limiting factor in catfish production, and disease outbreaks are not uncommon even on well-run facilities. A dead fish.About 45 percent of inventory losses on catfish fingerling farms are attributable to infectious diseases. Corresponding survey data for food-sized fish are lacking. Of the overall catfish losses caused by infectious disease, approximately 60 percent are the result of single or mixed bacterial infections, 30 percent result from parasitic infestation, 9 percent from fungal infections, and 1 percent are of viral etiology. Multiple or mixed infections often occur in pond raised channel catfish making treatment decisions difficult. Economic losses resulting from infectious diseases are difficult to quantify because record keeping varies among farmers and many diseases go unreported. Nevertheless, infectious disease is believed to cost producers many millions of dollars in direct fish losses each year. In addition, infectious diseases influence profitability by increasing treatment costs, reducing food consumption by fish, increasing feed conversion ratios, and causing harvesting delays. Fish-eating birds may also be attracted to ponds with sick and dying fish causing further losses. There are several disease syndromes for which the etiology remains in question, such as channel catfish anemia (CCA), which has also been referred to as "no blood disease". Another syndrome is visceral toxicosis of catfish (VTC), believed to be caused by a toxin. Once a disease outbreak occurs, effective health management requires three basic steps: problem identification, diagnosis, and corrective management--all of which must be performed in a timely manner to avoid further losses. Whenever multiple factors contribute to the disease process, it makes the diagnosis more difficult and often complicates corrective management.
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