64 SEPTEMBER 2014 • WORLD AQUACULTURE • WWW.WAS.ORG Alligator farming is a welldeveloped industry in Louisiana that currently contributes about US$60 million of farm-gate value to the state’s agricultural economy. The industry is based on production of wild stock obtained under regulatory oversight of the Louisiana Department of Wildlife and Fisheries (LDWF) through its highly successful alligator management program. The LDWF permits farmers to raise alligators obtained from the wild and requires that a specified proportion of farmed animals be returned to the wild to maintain populations. Farmers collect eggs of American alligator Alligator mississippiensis during the nesting season and incubate them on their farms. Hatchlings are stocked into temperature-controlled production houses and raised to a marketable size of 1.25 m in about 16 months. Skins, which enter the luxury leather market, are the most valuable item produced, but alligator meat is also sold domestically throughout the United States and exported around the world. In the early days of alligator farming, Louisiana producers fed meat obtained from various sources, often dead chickens from poultry farming operations and animal carcasses obtained from fur trappers. As production grew, the need for dry diets that could be handled easily and stored without refrigeration became increasingly important, and feed companies began to produce compounded diets for alligator aquaculture, similar to those used in intensive fish culture. Dry, extruded feeds are now the industry standard in alligator production operations. Despite the widespread use of compounded diets, very little is known about the nutritional needs of captive-reared alligators. Feed companies ensure their products produce the growth results their customers expect by producing well-fortified diets that are unlikely to possess deficiencies of any essential nutrients. Typically these diets are high-protein, high-fat formulations that utilize large amounts of animal products to satisfy the perceived needs of a carnivore. They are expensive and some of the nutrients they provide are not well utilized. This results in greater than necessary feed costs and requires increased sanitation measures to remove waste nutrients from the production environment. Thus, improvements in the nutrient balance of alligator feeds can be expected to reduce production cost, provide better environmental conditions for growing alligators and lead to cleaner effluents discharged from production facilities. Improvement of Diets for Alligator Aquaculture Robert C. Reigh and Millie B. Williams Recent Nutrition Research Like other farmed animals, alligators have specific minimum dietary requirements for certain nutrients that must be consumed in sufficient quantity to support growth, reproduction and good health. Unlike terrestrial livestock and poultry, and some farmed aquatic species, such as salmon, trout and channel catfish, the minimum dietary requirements of the American alligator are unknown. Nonetheless, the nutritional needs of the alligator can be estimated based on knowledge of its natural feeding habits and the known nutritional needs of other aquatic species, which already have been determined. While critical differences exist among species, reasonable assumptions can be made. For example, to maintain good health, all animals must consume protein to obtain the ten essential amino acids that cannot be synthesized by the body. Virtually all animals studied to date require the same ten dietary essential amino acids, as well as vitamins, minerals and some fatty acids; most other compounds can be synthesized by the body as needed. Different feedstuffs contain different amounts of these critical amino acids and animal proteins are generally better sources of dietary essential amino acids than plant proteins. However, despite nutritional differences among feedstuffs, many kinds of ingredients can be used in animal feeds if enough information is available to allow ingredients to be mixed in ways that provide proper nutrition at reasonable cost. When formulating a diet, the amount of protein and energy required to produce a desired growth response is a major consideration. Protein intake is an important factor affecting animal growth because the quantity and quality of dietary protein, its amino acid composition, greatly affects tissue production. Under optimum environmental conditions, the more high-quality protein an animal consumes, the faster its growth rate, up to a point beyond which there is no further increase as a result of the limits of metabolism. At that point, unused dietary protein is converted to fat and the nitrogen it contained is excreted as ammonia. The loss represents money wasted on unutilized protein, plus the added expense of removing excess ammonia from the production system. So what changes are needed? The research begun several years ago at Louisiana State FIGURE 1. Growth of American alligators fed one of four diets with different digestible energy to digestible protein ratios.
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