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Chapter 7 – Nutrition and Feeding of Litopenaeus vannamei - 125 - Chapter 7 Nutrition and Feeding of Litopenaeus vannamei in Intensive Culture Systems by Peter Van Wyk Elements of a good feeding program Feeding is one of the most critical aspects of shrimp husbandry. A good feeding program is necessary for shrimp to grow at their maximum potential. Feed represents one of the most significant operating expenses for most semi-intensive and intensive aquaculture operations. Often feed costs represent the single highest operating expense (50%) for an aquaculture enterprise. A well-managed feeding program insures that the feed is utilized efficiently. There are many things that a producer must do to guarantee a successful feeding program: 1) Feed a high quality diet that is formulated to meet the nutritional requirements of the shrimp and is manufactured from high quality, digestible ingredients; 2) Use only prepared feeds that are attractive, palatable and appropriate in size for the shrimp; 3) Maintain feed quality by utilizing proper feed storage and handling procedures; 4) Present the feed in quantities and frequencies that are appropriate for the number and size of the shrimp in the population being fed; 5) Distribute the feed evenly over the culture area to ensure that all the shrimp have equal access to the feed. 6) Make timely adjustments to the feeding regime based on water quality and the shrimp appetite. Nutritional Requirements The nutrients required by cultured species can be broadly classified as proteins, carbohydrates, lipids, vitamins and minerals. The optimum levels of these nutrients vary from one species to the next. Protein Requirements Protein makes up 65 to 70% of the dry weight of a shrimp, and is a major component of muscle. Protein in shrimp diet is the source of amino acids, which serve as building blocks for the shrimp’s own proteins. There are 20 different amino acids, but only 10 of these are considered to be essential in the diet. The rest can be synthesized by the shrimp from the Chapter 7 – Nutrition and Feeding of Litopenaeus vannamei - 126 - 10 essential amino acids. Strictly speaking, shrimp do not have a minimum protein requirement. Rather, they have minimum requirements for each of the ten essential amino acids (Table 7-1). Table 7-1: Recommended amino acid levels in commercial shrimp feeds, on an as-fed basis (after Akiyama and Tan, 1991). Percent of Feed Amino Acid Percent of Protein (%) 36% Protein 38% Protein 40% Protein 45% Protein Arginine 5.8 2.09 2.20 2.32 2.61 Histidine 2.1 0.76 0.80 0.84 0.95 Isoleucine 3.5 1.26 1.33 1.40 1.58 Leucine 5.4 1.94 2.05 2.16 2.43 Lysine 5.3 1.91 2.01 2.12 2.39 Methionine 2.4 0.86 0.91 0.96 1.08 Phenylalanine 4.0 1.44 1.52 1.60 1.80 Threonine 3.6 1.30 1.37 1.44 1.62 Tryptophan 0.8 0.29 0.30 0.32 0.36 Valine 4.0 1.44 1.52 1.60 1.80 The amino acid requirements for shrimp have not been well defined because shrimp do not efficiently utilize crystalline amino acids from the purified diets used to study amino acid requirements. As a general rule, however, the amino acid requirements of a species closely mirror the amino acid composition of their muscle tissue (Lim and Persyn, 1989). The amino acid composition of shrimp feeds is largely based on the amino acid composition of shrimp muscle (Akiyama, et al., 1991). Feed formulators mix and match different sources of protein, each with different amino acid profiles, so that the diet meets the minimum requirement for all 10 essential amino acids. The formulator must also take into account the digestibility of each of the feed ingredients and the availability of the amino acids. Fishmeal is generally considered to be the highest quality protein source because the amino acid composition of fishmeal closely matches that of shrimp. For commercial growout diets, krill and Artemia meal are better than fishmeal, but they are more expensive. However, they are used in larval and maturation diets. Most commercial shrimp feeds formulated for intensive culture systems contain between 35 and 50% protein. If the level of protein in the feed is too low, growth rates will be reduced. Severe protein deficiencies may actually lead to weight loss if the proteins in shrimp muscle tissue are used to maintain other vital functions. Excess protein in the diet may also inhibit growth (Lim and Persyn, 1989). The excess protein will be metabolized by the shrimp as a source of energy, and nitrogen will be excreted as ammonia. Protein requirements are fairly high for postlarvae and small juveniles, but decline as the shrimp grow larger. Table 7-2 gives the recommended protein levels for different sizes of shrimp in high-intensity culture systems. Chapter 7 – Nutrition and Feeding of Litopenaeus vannamei - 127 - Table 7-2: Recommended protein levels for different sizes of shrimp in high-intensity culture systems. Shrimp Size (g) Recommended Feed Protein Level 0.002 – 0.25 50 % 0.25 – 1.0 45% 1.0 – 3.0 40% >3.0 35% Lipids Lipids, or fats, are a group of organic compounds that include free fatty acids, phospholipids, triglycerides, oils, waxes and sterols. Lipids function as an important energy source for shrimp. In addition to their value as an energy source, lipids serve as a source for essential fatty acids. Fatty acids are chain-like organic molecules with many repeating units. Each “link” in the chain contains a carbon atom. Fatty acids differ in chain length and in the degree of saturation (number of double bonds and hydrogen atoms). A highly unsaturated fatty acid will have many double bonds, and few hydrogen atoms. These fatty acids appear to be important in the structure of cellular membranes. Four fatty acids are considered essential fatty acids in shrimp, because they are required in the diet and cannot be synthesized from other compounds. The essential fatty acids are: linoleic acid (18:2n6), linolenic (18:3n3), eicosapentaenoic acid (20:5n3), and decosahexaenoic acid (22:6n3) (Kanazawa an Teshima, 1981). Table 7-3 gives the recommended levels essential fatty acids in shrimp diets. Table 7-3: Recommended fatty acid levels in commercial shrimp feeds (after Akiyama, et al. 1991) Fatty Acid Percent of Feed Linoleic Acid (18:2n6) 0.4 Linolenic Acid (18:3n3) 0.3 Eicosapentaenoic Acid (20:5n3) 0.4 Decosahexaenoic Acid (22:6n3) 0.4 Phospholipids are compounds consisting of glycerol, fatty acids and phosphoric acid. They are important components of cell membranes and play an important role in lipid metabolism. Sterols are required by crustaceans as a precursor for maturation and molting. Lipids are often added to fish diets in the form of fish oil, soybean and sometimes squid oil. Table 7-4 gives the recommended lipid levels in shrimp diets for high-intensity culture Chapter 7 – Nutrition and Feeding of Litopenaeus vannamei - 128 - systems as a function of shrimp size. The recommended total lipid level in the diet decreases with increasing shrimp size. Table 7.4: Recommended lipid levels for shrimp diets used in intensive culture. Shrimp Size (g) Lipid Level (%) 0.002 – 0.2 15 % 0.2 – 1.0 9 % 1.0 – 3.0 7.5 % >3.0 6.5 % Carbohydrates Carbohydrates serve as an inexpensive energy source in shrimp diets. Starches, sugars and fiber are the main forms of carbohydrates. Organisms differ in their ability to use carbohydrates as an energy source. Carnivores, whose diets contain high levels of protein, tend to use protein as an energy source and often are unable to metabolize carbohydrates effectively. Omnivorous and herbivorous fish and shrimp utilize carbohydrates effectively. While no absolute carbohydrate requirement has been found for shrimp, carbohydrates in the diet can have a “protein sparing” effect for species thatare able to utilize carbohydrates efficiently. That is, if carbohydrates are present in sufficient quantity in the diet, the protein requirement is reduced. Vitamins Vitamins are organic compounds that are required in the diet in relatively small quantities for normal growth and development. Vitamins are classified as either water soluble or fat soluble. The B-complex vitamins are water soluble and are required in relatively small quantities. These vitamins function primarily as coenzymes in various metabolic processes. Three water-soluble vitamins are required in larger quantities and have functions other than coenzymes. These are Vitamin C, inositol, and choline. Vitamin C and choline are often added separately, as these vitamins are required in relatively large quantities. The fat- soluble vitamins are Vitamins A, D, E and K. Fish and shrimp diets usually are fortified with a vitamin premix that contains all of the 16 essential vitamins. The vitamin requirements for marine shrimp are affected by many different factors, including shrimp size, age, growth rates and environmental factors (Akiyama, et al., 1991). Young juvenile shrimp may require 50% higher vitamin levels in their diets than adult shrimp. Shrimp cultured in intensive culture systems typically require much higher vitamin concentrations than are required by shrimp grown at low densities. Vitamin deficiencies frequently result in symptoms, such as physical deformities, blindness, erratic swimming behavior, lethargy and poor growth. The physical symptoms displayed differ, depending on which vitamin is deficient in the diet. Vitamin C deficiency is associated with “Black Chapter 7 – Nutrition and Feeding of Litopenaeus vannamei - 129 - Death” disease, characterized by melanized lesions of subcuticular tissues. Typically, feed manufacturers overfortify shrimp diets with vitamins. This is done for several reasons. Detailed information about shrimp vitamin requirements is lacking. Overfortification is cheap insurance against crop losses due vitamin deficiencies. In addition, many vitamins are unstable compounds that are easily destroyed during manufacture and feed storage. Vitamin C, in particular, has a very short half-life at room temperature. Stable forms of Vitamin C, such as Stay-C, have a much longer shelf life than the non-stabilized form of Vitamin C. Because shrimp are slow feeders, the feed may sit in the water for several hours before it is consumed. Significant quantities of water-soluble vitamins may leach into the surrounding water before the feed is eaten. Minerals Minerals are inorganic elements required for various metabolic processes. Minerals required in large quantities are called major minerals. These include calcium, phosphorus, magnesium, sodium, potassium, chloride and sulfur. Calcium is required for exoskeleton formation, muscle contraction and osmoregulation. Shrimp are able to absorb calcium directly from the water, and shrimp living in seawater do not need calcium supplements in the diet (Davis, 1991). However, diets for shrimp cultured in near-freshwater systems should contain up to 2.5% calcium. Higher levels of calcium should be avoided because in high concentrations calcium appears to interfere with the bioavailability of phosphorus (Davis, 1990). Phosphorus is required for exoskeleton formation and is an essential component of phospholipids, nucleic acids, ATP, and many metabolic intermediates and coenzymes. Davis (1990) demonstrated that the phosphorus requirement for Litopenaeus vannamei was dependent upon the calcium content of the diet, and that in the absence of calcium, 0.34% phosphorus was sufficient for normal growth and development. Shrimp diets often contain up to 1% dietary phosphorus. Unlike calcium, phosphorus is not absorbed in significant quantities from the water and must be supplied in the feed (Davis, 1991). Calcium and phosphorus are often added to the diet in the form of dicalcium phosphate. Some minerals are required in minute quantities and are called trace minerals. Trace minerals include iron, iodine, manganese, copper, cobalt, zinc, selenium, molybdenum, fluorine, aluminum, nickel, vanadium, silicon, tin and chromium. The trace minerals are generally added to the diet in a mineral premix. Sometimes vitamins and minerals are combined into a single vitamin-mineral premix. Shrimp Feeds Formulated Diets There is a saying: “Man cannot live on bread alone.” The same is true of shrimp. A diet consisting of a single feed ingredient is not likely to be able to provide all of the nutrients required for normal growth and development. This is why aquaculturists usually feed their Chapter 7 – Nutrition and Feeding of Litopenaeus vannamei - 130 - animals a formulated diet. Formulated diets are mixtures of different feed ingredients mixed in set proportions to provide the desired quantities of nutrients. A wide variety of different feed ingredients are used in commercial shrimp feed formulations. Common ingredients used in commercial shrimp feeds include soybean meal, fish meal, squid meal, shrimp head meal (cooked), wheat flour, wheat middlings, lecithin, cholesterol, starch, dicalcium phosphate, vitamin and mineral mixes, and binders. Formulated diets may be either supplemental or complete. Feeds that are applied to supplement natural food sources are called supplemental diets. Shrimp grown in ponds at very low densities may be able to survive and grow without any supplemental feed input to the pond. Under these conditions, naturally occurring plants and animals serve as the food source for the culture species. At higher densities, natural productivity is insufficient to support the nutritional requirements of the culture species, so prepared feeds must be included to supplement the nutrition obtained from natural food sources. Supplemental diets rarely meet the nutritional needs of the culture species, but are adequate when natural foods are available. Where natural foods are not available, such as in tank-based culture systems and high-density pond culture systems, nutritionally complete diets must be provided. Complete diets contain all of the essential nutrients in amounts sufficient for normal growth and development of the cultured organism. It is also necessary that these nutrients must be available in a form that is digestible. Complete diets typically have higher protein, vitamin, and mineral levels than supplemental diets. The majority of commercial shrimp feeds available today are considered to be supplemental feeds. Shrimp nutrition is very complex, and the current state of knowledge about shrimp nutritional requirements is incomplete. While some very good shrimp diets are available commercially, it is doubtful whether any of these can be considered a true complete feed. Growth rates of tank-reared shrimp that rely on prepared diets for 100% of their nutritional needs do not match the growth rates that are frequently observed in productive pond environments. However, the shrimp maintained on these diets develop normally and are generally healthy. Feed Processing Shrimp are benthic feeders, so shrimp feeds must be processed into a sinking pellet. Most shrimp feeds are manufactured either using a steam pelleting process or an extrusion process. Steam pelleting uses a combination of moisture, heat and pressure to form finely ground feed ingredients into a dense, tightly bound pellet Figure 7-1: Pelleted Shrimp Feed Chapter 7 – Nutrition and Feeding of Litopenaeus vannamei - 131 - (Figure 7-1). The feed ingredients are finely ground and mixed together in the proper proportions. Moisture is added and the ingredients are thoroughly blended into a pasty mash. The mash is fed into a pelleting mill that uses an auger to compress the mash. Steam isintroduced into the pelleting chamber, which causes the starch in the feed mixture to gelatinize and helps bind the ingredients together. Binders are often used to complement the binding provided by gelatinized starch. The feed mixture is then forced through holes in a die plate located at the end of the chamber. The diameter of the pellet is determined by the diameter of the holes in the die plate. Extruded feeds are formed using a similar process, but much higher temperature and pressure is generated within the barrel of the extruder. This results in more complete gelatinization of the starches contained in the feed ingredients, so additional binders are not required. Extruded feeds often are less dense than steam pelleted feeds because rapid release of the steam from the feed pellets after they pass through the die plate causes the pellets to expand. The extrusion process is often used to create floating pellets, which are popular for feeding fish. The extrusion process is typically carried out at a slightly lower temperature using formulations with less starch to obtain a sinking pellet. Pellet Stability Good water stability is important in the preparation of shrimp feeds, regardless of pelleting process,. Shrimp are slow feeders and a pellet may sit in the water up to four or five hours before it is eaten. To evaluate the feed stability in water, place several pellets in a beaker of water. The pellets should remain largely intact for up to four hours. Periodic gentle swirling of the water in the beaker can help simulate the effects of water movement on pellet stability. Feeds with poor water stability are not efficiently utilized by the shrimp and will foul the water. Pellet Diameter The required diameter of the feed pellets varies depending on shrimp size. Postlarvae and young juveniles are too small to eat a formed pellet. Feeds for these shrimp are made by grinding a pelleted feed and passing the ground feed through a series of sieves to obtain feed particles of a uniform diameter. Because pellet integrity is not as critical an issue for ground diets, postlarval and juvenile feeds are frequently manufactured using a cold pelleting process. Cold pelleting is less destructive to the vitamins in the feed. Shrimp that weigh less than one gram are typically fed ground feeds. Larger shrimp are able to eat pelleted diets. Table 7-5 lists recommended particle or pellet sizes for shrimp of different sizes. Chapter 7 – Nutrition and Feeding of Litopenaeus vannamei - 132 - Table 7-5: Recommended pellet diameters for shrimp of different sizes. Shrimp Size (g) Pellet Diameter 0.002 – 0.02 400 – 600 µm 0.02 – 0.08 600 – 850 µm 0.08 – 0.25 850 – 1200 µm 0.25 – 1.0 1200 – 1800 µm 1.0 – 2.5 3/32” pellet (2.4 mm) >2.5 1/8” pellet (3.2 mm) When making the transition from one pellet size to the next, it is a good idea to feed a mixture of the two sizes of pellets for 5-7 days to allow the shrimp time to get used to the larger pellet size before discontinuing the smaller pellets. Feed Application Feeding Rates It is critical that feed be applied in the correct amounts and at the correct times throughout the culture period. Feed rates must be constantly adjusted to account for shrimp growth, mortality and appetite. If the feeding rate is too low, the shrimp will not grow well, and overall production will suffer. Underfeeding may also result in cannibalism, especially at high densities. Overfeeding also causes problems. Besides being wasteful, uneaten feed can contribute to deterioration of water quality in the culture system. The organic material in the feed becomes a substrate for heterotrophic bacteria, which metabolize the protein in the feed and give off ammonia. Elevated ammonia levels in the water suppress shrimp growth and increase the shrimp’s susceptibility to disease. The oxygen demand of these bacteria can lead to low dissolved oxygen levels in the system, inhibiting shrimp growth. Some heterotrophic bacteria release substances into the water, which can cause the shrimp to be off-flavor. Overfeeding causes overall feed conversion values to increase, since some of the leftover feed, and inefficient assimilation of the feed that is consumed. There are many factors that affect the amount of feed the shrimp will eat. Feed consumption varies with feed type, shrimp size, water temperature, stocking density, weather, water quality and health. Shrimp culturists must take all of these factors into account in order to maximize the efficiency of the feeding program. Temperature has an especially pronounced effect on feed consumption and growth. For L. vannamei, feed consumption is optimal when water temperatures are between 27°C and 31°C (81°F and 87°F). Feed consumption decreases both above and below these Chapter 7 – Nutrition and Feeding of Litopenaeus vannamei - 133 - temperatures. Feed consumption may be reduced by 50% when the water temperature drops to 24°C (72°F), and ceases altogether when water temperature drops below 20°C (68°F). Feed Tables Feed tables have been developed that give a recommended feed rate, expressed as percent of bodyweight per day (% BW/Day), for animals of different sizes. As a general rule, small animals are fed at a higher percentage of their bodyweight per day than are large animals. This is because small animals will generally have a higher metabolic rate than large animals. Table 7-6 shows a typical feed table for L. vannamei cultured in high- density tank systems. To calculate the daily feed allowance for a population of shrimp, multiply the total biomass of the shrimp population by the recommended feed rate from the feed table: Daily Feed Allowance = Total Biomass x % BW/Day 100 % (7.1) The total biomass of the shrimp population is calculated by multiplying the estimated number of shrimp in the population by the average weight of the shrimp: Total Biomass = Total Number of Shrimp in the Population x Average Weight (7.2) Accurate information about the average weight and total number of shrimp in the population is required to correctly calculate the daily feed allowance. The shrimp population should be sampled at least every other week to determine the average shrimp Table 7-6: Feed Table for High-Intensity Tank Production of Litopenaeus vannamei. Average Shrimp Wt. (g) Feed Rate (% BW/day) <.1 35 – 25 0.1 - 0.24 25 – 20 0.25 – 0.49 20 – 15 0.5 – 0.9 15 – 11 1.0 – 1.9 11 - 8 2.0 – 2.9 8 – 7 3.0 – 3.9 7 – 6 4.0 – 4.9 6 – 5.5 5.0 – 5.9 5.5 – 5.0 6.0 – 6.9 5.0 – 4.5 7.0 – 7.9 4.5 – 4.25 8.0 – 8.9 4.25 – 4.0 9.0 – 9.9 4.0 – 3.75 10.0 – 10.9 3.75 – 3.5 11.0 – 11.9 3.5 – 3.0 12.0 – 12.9 3.25 – 3.0 13.0 – 13.9 3.0 – 2.75 14.0 – 14.9 2.75 – 2.5 15.0 – 15.9 2.5 – 2.3 16.0 – 16.9 2.3 – 2.1 17.0 – 17.9 2.1 – 2. 18.0 – 18.9 2.0 – 1.9 19.0 – 19.9 1.9 – 1.8 20.0 – 20.9 1.8 – 1.7 Chapter 7 – Nutrition and Feeding of Litopenaeus vannamei - 134 - weight. A minimum sample size of at least 30 shrimp should be used to calculate the average weight of the population. If there is large variation in size within the population, the sample size should be increased to 60 shrimp per sample. Best results are obtained by weighing each shrimp in the sample individually after blotting off excess water with a paper towel. Estimation of the total number of shrimp in the population is more difficult. The number of shrimp in the population at any given time is equal to the number of shrimp stocked multiplied by the fraction of shrimp still surviving at that time: No. shrimp at time t =Number of shrimp stocked x Fraction surviving to time t (7.3) Survival rates are very difficult to estimate. In tank culture systems, dead shrimp can often beremoved from the tank and counted. Although observed mortality is very helpful in estimating survival in a tank, population estimates based on observed mortality rates are nearly always overestimates of the true number of shrimp. This is because it is very difficult to account for all of the mortality, especially for very small shrimp. Some of the shrimp may be consumed by other shrimp, while other mortalities may simply escape notice. Standardized survival curves based on historical average survival rates are often used to estimate shrimp numbers in a population. Survival curves may be linear (assuming a constant mortality rate), or may have varying slopes over different portions of the growout cycle. Often curves are constructed to reflect heavier mortality rates during the nursery phase than in subsequent phases of the growout. Even if standard survival curves are used to estimate the population of a culture tank, adjustments will be necessary in cases where survival is unusually high or low. It is important to note that feeding tables only provide a guide to the amount the shrimp will eat under optimal conditions of temperature, density, water quality, etc. Following these feed tables religiously will invariably lead to overfeeding when conditions are sub-optimal. As an example, following a low dissolved oxygen condition, feeding activity is typically depressed. If the feed rates recommended by the feed tables are followed, much of the feed will go uneaten. The uneaten feed may even exacerbate the dissolved oxygen problem. High ammonia levels will also suppress shrimp appetites, and overfeeding will contribute to even higher levels ammonia in the tank. The feed table should serve only as a guideline for determining the daily feed allowance. Chapter 7 – Nutrition and Feeding of Litopenaeus vannamei - 135 - Demand-based Feeding Demand-based feeding is an alternative to using a feed table. With this method, the feed allowance is adjusted up or down depending on the feeding activity of the shrimp. At each feeding, the technician estimates the amount of feed that the shrimp can consume during the time interval between feedings. If a significant amount of feed remains from the previous feeding, the amount fed at the next feeding should be reduced by at least 10 percent. If all of the feed has been consumed between feedings, the feed amount can be increased by 10 percent. This approach to feeding ensures that the feed rates will be appropriate for the conditions in the tank. In clear water, it is easy to see how much of the feed is being eaten. However, if a dense algal bloom develops in a tank, it may be difficult to see uneaten feed on the bottom of the tank. One way to determine if the shrimp are eating all of the food is to place feed trays in the raceway. The trays can be lifted from the water to see if the feed has been eaten. Feeding Frequency The number of feedings per day is determined by pellet stability and by the rate at which the feed is consumed, digested and metabolized by the shrimp. Dividing the daily feed ration into multiple feedings, spaced several hours apart, improves feed conversion ratios and growth rates. In addition, feeding only what the shrimp can consume in 3 or 4 hours reduces losses of nutrients due to leaching. It is not clear whether or not there is any benefit derived from feeding the shrimp throughout the 24-hour period. While L. vannamei are active at night, they may not be actively feeding during this time period. Robertson et al. (1993) reported that L. vannamei receiving four feedings a day during daylight hours performed as well as, or better than, shrimp fed around the clock. Small shrimp metabolize their food faster than large shrimp, and generally require more feedings per day. Postlarval shrimp require frequent feedings because they have very high metabolic rates, but are not able to store much feed in their guts. Ideally, postlarvae should be fed every 2-3 hours. Longer intervals between feedings may result in heavy losses due Figure 7-2: Weighing out shrimp feed Chapter 7 – Nutrition and Feeding of Litopenaeus vannamei - 136 - to cannibalism. Automatic feeders, which dispense small amounts of feed at programmed intervals or on a continuous basis, can be used to make sure the shrimp are fed in a timely manner. As the shrimp grow the feeding frequency can be decreased. Four feedings spaced three hours apart during daylight hours works well for juveniles larger than 1 gram in size. Feed Distribution Feed may be distributed to shrimp either by hand or by automatic feeders (Figure 7-3). The feeding method used is a function of the culture system, requirements of the culture organism and the preferences of the aquaculturist. Hand feeding is frequently practiced when feeding animals held in tanks or raceways, especially when the animals are small. Hand feeding allows the technician to modify the feed distribution in accordance with the feeding response. Hand feeding may be impractical when a large number of tanks must be fed because it is very time-consuming. Automatic feeders dispense a given volume of feed on a timed basis. Automatic feeders operate by a wide variety of mechanisms. Automatic feeders for larvae, fry, or small juveniles often consist of a plate or belt onto which feed is loaded (Figure 7-3). The plate or belt is rotated in a manner that causes feed to fall off into the water at a steady rate throughout the day. Scatter feeders distribute feed from a hopper suspended over the water at timed intervals. Scatter feeders have a plate at the bottom of the hopper with vanes extending radially from the center of the plate. At timed intervals, feed is released from the hopper and the plate spins around, casting feed in a 360° arc around the feeder. Scatter feeders can be modified for raceways to throw the feed out in a single 45-degree direction. Large- scale operations with multiple raceways often use a conveyer system to load the hoppers. These consist of tubes through which feed is moved by a variety of means. Some use pneumatic blowers to move the feed, while others use augers or a similar mechanism. Figure 7-3: Automatic Belt Feeder Chapter 7 – Nutrition and Feeding of Litopenaeus vannamei - 137 - Feed Conversion Ratios An important measure of how well the feed is utilized by the animals in the culture system is the Feed Conversion Ratio or FCR. The Feed Conversion Ratio measures the number of pounds of feed required to produce a pound of shrimp. The following formula is used to calculate feed conversion: Feed Conversion Ratio = Total Weight of Feed Applied TotalWeightGained (7.4) The lower the FCR value, the more efficiently the feed is being utilized. Generally speaking, FCR values less than 2.0 are considered good. High FCR values may result from nutritionally deficient feeds, overfeeding, poor water quality or crowding. Whenever high FCR values are obtained, it is important to take a critical look at the feeding program and production process to try to identify the causes. Feed Storage Feed storage is an important and often neglected aspect of the feed management program. Aquaculture feeds are highly perishable. Inadequate storing and handling of feed can lead to nutrient losses, rancidity, mold growth and rodent infestations. Many of the vitamins in the feed are unstable at high temperatures and significant losses will occur if the feed is stored at high temperatures or exposed to ultraviolet light. Vitamin C (ascorbic acid) is particularly prone to degradation. At room temperatures, ascorbic acid has a half-life of less than a month. Two-month old feed will have a small fraction of the amount of ascorbic acid that was originally added to the feed. StabilizedVitamin C (Stay C) is much more stable, but still is degraded over time. Feeds that are high in lipids often will become rancid when stored in warm, oxidative environments. Rancid feeds are unpalatable to the shrimp and are deficient in Vitamin E. Reduced growth rates are commonly seen in shrimp receiving rancid feeds. Rancid feeds have a very distinctive odor. The technicians should be sure to smell a handful of feed from each feed sack that is opened before using the feed to determine if the feed has gone rancid. Molds will often develop on feeds that are stored in humid or moist environments. Molds produce toxins that can be very damaging to the shrimp. Molds of certain species in the genus Aspergillus produce aflatoxins, which can cause severe liver damage to the shrimp. Given the correct environment, molds grow quickly on the feed. Feed does not have to be old to be moldy. Occasionally feed will already have mold growing on it when it arrives from the feed mill. This can happen when the feed is placed into the feed bag while it is still hot, or if the feed not been dried sufficiently. When hot feed cools, moisture condenses on the feed. The dark, humid environment inside the feed sac is a perfect incubator for Chapter 7 – Nutrition and Feeding of Litopenaeus vannamei - 138 - mold growth. When receiving feed, inspect a few bags to make sure that the no mold is present. If mold is detected, the shipment should be rejected. Before using the feed from any feed bag, inspect the feed for mold. If even a small amount of feed in a bag appears to be moldy, discard the entire bag. Significant quantities of mold toxins will be present throughout the bag. Unless the feed is stored in a sealed room with narrow clearances around the door jam, the feed will soon be infested with rodents. Besides eating the feed, rodents will urinate and defecate in the feed sacks, ruining the feed. To avoid the kinds of problems described above, feed should be stored in a dry, cool, rodent-resistant storage shed. If possible the feed storage room should be air-conditioned. The air conditioner will help maintain a low humidity, as well as a cool storage environment. A “first-in, first-out” inventory management strategy should be employed to make sure that feed gets used before its expiration date. Ideally, feed should be used within one month of purchase. If storage conditions are ideal, feed can be used for up to three months, although the quality of the older feed will not match that of feed less than one month old. Sources of Shrimp Feeds The following is a list of U.S. shrimp feed manufacturers: Bonney, Laramore, and Hopkins, Inc. 5600 Highway U.S. 1 North Ft. Pierce, FL 34946 Tel: (561) 971-2925 Burris Mill and Feed , Inc. 1012 Pearl Street Franklinton, LA 70438 Tel. (504) 839-3400 Fax: (504) 839-3404 Cargill Nutrena Feeds 801 South Poplar Street Florence, AL 35630 Tel. (205) 764-1331 Ralston Purina International Checkerboard Square –11T St. Louis, MO 63164 Tel. (314) 982-2402 Fax. (314) 982-1613 Rangen Feeds 115 13th Ave. S. Buhl, ID 83316 Tel. (800) 657-6446 Fax (208) 543-4698 Rangen Feeds Angleton, TX Tel. (979) 849-6757 Star Milling Company PO Box 728 Perris, CA 92370 Tel. (909) 657-3143 Fax (909) 943-2400 Zeigler Brothers, Inc. PO Box 95 Gardners, PA 17324-0095 Tel. (800) 424-2033 Fax (717) 677-6826 Chapter 7 – Nutrition and Feeding of Litopenaeus vannamei - 139 - Literature Cited Akiyama, D. M., W.G. Dominy, and A.L. Lawrence. 1991. Penaeid shrimp nutrition for the commercial feed industry: Revised. Pages 80-98 in D.M. Akiyama and R.K.H. Tan, editors. Proceedings of the Aquaculture and Feed Processing and Nutrition Workshop. Singapore, Republic of Singapore. Davis, D.A. 1990. Dietary mineral requirements of Penaeus vannamei: evaluation of the essentiality for thirteen minerals and the requirements for calcium, phosphorus, copper, iron, zinc, and selenium. Ph.D. Dissertation, Texas A&M University, College Station, TX, USA. Davis, D.A. and D.M. Gatlin III. 1991. Dietary mineral requirements of fish and shrimp. Pages 49-67 in D.M. Akiyama and R.K.H. Tan, editors. Proceedings of the Aquaculture and Feed Processing and Nutrition Workshop. Singapore, Republic of Singapore. Kanazawa, A., and S. Teshima. 1981. Essential amino acids of the prawn. Bul. Jap. Soc. Sci. Fish. 43(9): 1111-1114. Lim, C. and A. Persyn. 1989. Practical Feeding – Penaeid Shrimps. In, Editor, Tom Lovell. Nutrition and Feeding of Fish. Van Nostrand Reinhold. New York. pp. 205- 222. Robertson, L., A.L. Lawrence, and F.L. Castille. 1993. Effect of feeding frequency and feeding time on growth of Penaeus vannamei (Boone). Aquaculture and Fisheries Management 24: 1-6. Chapter 7 – Nutrition and Feeding of Litopenaeus vannamei - 140 -
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