WWW.WAS.ORG • WORLD AQUACULTURE • SEPTEMBER 2014 65 University is investigating the practical nutritional needs of American alligator to provide recommendations for improving the diet of farm-raised animals. One long-term goal is the development of plant-based diets for alligator aquaculture. Digestibility studies showed that alligators efficiently utilized crude protein and energy in corn, soybean meal, soy protein concentrate, wheat gluten and menhaden fish meal, and the availability of dietary essential amino acids in these feedstuffs often exceeded 90 percent when they were provided at concentrations of 30-45 percent of diet weight (Reigh and Williams 2013). Amino acid availability coefficients indicated that alligators efficiently utilize protein from an assortment of plant products of diverse chemical composition. The LSU research also has shown that 45 percent dietary protein is sufficient for alligators fed a diet similar in composition to the commercial diet now used by most Louisiana farmers. A 45 percent protein diet produced growth comparable to a similar formulation containing 55 percent protein and generated less ammonia in the production environment (Reigh et al. 2013). Most recently a study was conducted to determine the appropriate dietary energy to protein ratio for alligators fed a plant-based diet. Latest Feeding Trial Eighty young-of-year alligators (approximately 100 g mean body weight) were stocked, two per tank, in 0.3-m2 tanks in a recirculation system and fed one of four diets for 225 days. Water temperature was 31 C; water depth was 7 cm at the beginning of the study and increased to 15 cm at the end. Tanks were flushed several times per week to remove solid wastes and the biofilter was flushed daily. Three, cold-pelleted, experimental diets containing 43-47 percent digestible protein and graded digestible energy (DE) to digestible protein (DP) ratios of 42, 38, or 34 kJ DE/g DP were evaluated by comparing growth performance of alligators fed these diets to that of a control group fed the commercial diet most commonly used by Louisiana alligator farmers (56 percent crude protein). Primary components of the experimental diets were soybean meal (32-35 percent), wheat gluten (27-29 percent), menhaden fish meal (15-16 percent), yellow corn (11-16 percent), plus vegetable oil (1-12 percent), vitamin and mineral supplements, and water-soluble binder (all 1 percent), with all ingredient proportions expressed on a dry-weight of diet, as-fed basis. Ingredient composition of the commercial diet was proprietary, but its proximate composition and amino acid composition were determined by analysis. It was assumed, for the purpose of diet formulation, that the whole-body amino acid composition of alligator provided an approximation of dietary amino acid requirements. Data on available energy and available amino acids in feedstuffs, which had been obtained during previous digestibility trials, as well as concentrations of essential amino acids in the whole-body of young-of-year alligators (determined by analysis), were entered into a computer program that was used to formulate experimental diets to meet specific restrictions on protein content, DE to DP ratio and available essential amino acid composition. Diets were formulated to provide essential amino acids in quantities that were similar to those in alligator body tissues, so relative proportions of critical amino acids would remain consistent among the three dietary treatment groups. Alligators were fed to apparent satiation daily, and weighed and measured monthly. Results of the feeding trial indicated the diet containing 45 percent DP and 38 kJ DE/g DP produced gains in body weight that were not significantly different from those obtained with the control diet (Fig. 1). The amount of crude protein (54 percent) in dry feces of alligators fed the control diet also was significantly greater than the amount of protein (33-37 percent, dry) in feces of alligators fed the three experimental diets, suggesting dietary protein utilization was lower among alligators fed the highprotein commercial diet than among those fed lower-protein, plantbased experimental diets. Results of this study showed a diet consisting of more than 80 percent plant products was adequate for young-of-year alligator when the dietary essential amino acid balance was similar to that of alligator whole body. Results also indicated that American alligator can effectively utilize dietary carbohydrate of plant origin, although the limit of that capability has not been determined. These results suggest that plant products can be used as alternatives to animal products in compounded alligator diets and at relatively high inclusion rates in some cases. However, to maximize the value of plant products in alligator feeds, information is needed on the digestible protein/energy content and available amino acid content of a wide selection of ingredients available for use when economic conditions warrant a change in diet formulation. Next Step An upcoming experiment will test the 45 percent DP diet in a full-scale, 12-mo production trial to determine its effects on alligator growth, skin quality and muscle composition under simulated production conditions. Results of that study will identify future research needs and support additional recommendations on the improvement of diets for alligator aquaculture. Notes Robert C. Reigh and Millie B. Williams, Aquaculture Research Station, Louisiana State University Agricultural Center, 2410 Ben Hur Road, Baton Rouge, LA 70820-6103 USA Email: rreigh@agcenter.lsu.edu Acknowledgments This research was funded in part by the United States Department of Agriculture, Louisiana Department of Wildlife and Fisheries, Louisiana Agricultural Experiment Station, Louisiana Alligator Farmers and Ranchers Association, and Cargill Animal Nutrition. References Reigh, R.C. and M.B. Williams. 2013. Amino acid availability of selected plant products and fish meal for American alligator (Alligator mississippiensis). Aquaculture 412-413:81-87. Reigh, R.C., M.B. Williams and C.G. Lutz. 2013. Dietary needs of farm-raised alligators. Louisiana Agriculture 56(3):6-8. (www.lsuagcenter.com/en/communications/publications/agmag/ Archive/2013/Summer/Louisiana-Agriculture-Summer-2013.htm)
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