Robert Reigh

Alligator aquaculture ranks among the top five animal enterprises in Louisiana, with a current farm-gate value exceeding $82 million annually. While alligator farmers share many concerns common to livestock producers in general, alligator aquaculture presents a unique set of challenges. Unlike other types of livestock production, alligator farmers draw their farm stock from the wild under permitting authority of the Louisiana Department of Wildlife and Fisheries, which employs an extensive research and management program to ensure the well-being and sustainable use of Louisiana’s wild alligator populations. Farmers collect more than a half million eggs annually from wetland habitats for which the Department of Wildlife and Fisheries has set egg-harvest quotas. A majority of these wetlands are privately owned. Farmers establish lease agreements with landowners to collect eggs during the May-June alligator nesting season, which produces income for the landowner and incentive to maintain marginal land as wetland habitat for alligators. Eggs collected in the wild are transported to farms and incubated under controlled conditions to produce hatchlings for grow-out (Figure 1). Because eggs are available only once per year and collection costs are high, it is important to maximize egg-hatching success and optimize growth of each alligator-year class to maintain farm productivity. At present, however, there is limited science-based information on best practices for alligator husbandry, including optimum conditions for egg incubation and nutritional requirements for optimum growth.

Recent studies at the LSU AgCenter Aquaculture Research Station have focused on improving alligator feeds to increase nutrient utilization and allow greater cost control through use of alternative ingredients. Experiments have evaluated different protein concentrations and compositions in alligator diets; measured protein digestibility, energy digestibility and essential amino acid availability of ingredients of plant and animal origin; and tested plant-based diets to determine the value of plant products as substitutes for animal products in compounded feeds. Results have demonstrated that a nutritionally balanced feed containing up to 80 percent plant products — including soybean meal, wheat gluten and yellow corn — can be effectively utilized by alligator without negative effects on health or body composition.

Information on the efficiency with which alligators utilize nutrients in a variety of feedstuffs expands the range of ingredients producers may select to optimize dietary nutritional balance and product cost. Digestibility studies with a growing list of ingredients have been underway for years and will continue indefinitely as the nutrient-availability database expands. Knowledge of minimum dietary requirements for essential nutrients, all of which are unknown for alligators, is also necessary to truly optimize diet formulations. A study in progress at the Aquaculture Research Station is investigating requirements for lysine and methionine, two critical dietary-essential amino acids, as a first step in providing this information.

Also of interest are effects of incubation conditions on egg-hatching success and identification of husbandry practices that negatively affect skin quality. Recent incubation studies have shown that maintaining oxygen concentrations above the normal 21 percent level in air does not improve egg-hatching success. However, relative humidity is a critical factor affecting embryo development (Figure 2). Humidity of approximately 90 percent appears to be optimum.

A study in progress is investigating whether high-oxygen, or hyperoxic, incubation conditions promote faster closure of the umbilicus, the site of egg-sac attachment on a developing embryo (Figure 3). Failure of the umbilicus to close properly after a hatchling emerges from the egg creates a scar, which can significantly reduce the value of an alligator skin at harvest. Anecdotal evidence suggests hyperoxic conditions during embryonic development might reduce scarring, but this remains to be proven. Other skin-quality problems also are being investigated to determine causes and solutions, including possible nutritional or environmental factors that contribute to these costly conditions.

The AgCenter alligator research program is developed annually with input from an advisory group of farmers, Department of Wildlife and Fisheries personnel and private industry stakeholders. The goals of the program are to address the practical research needs of farmers involved in one of Louisiana’s major livestock industries while providing fundamental new information on the biology of the American alligator.

Robert Reigh is a professor and director of the LSU AgCenter Aquaculture Research Station.

Figure 1. Alligator hatchling emerging from an egg. The number on the shell identifies the clutch (nest) from which the egg was collected. Lines mark the area where the embryo was attached to the shell at time of collection. Eggs must remain upright until hatched. Photo by Robert Reigh

Figure 2. Eggs that failed to hatch due to below-optimum humidity during incubation contained embryos in a range of developmental stages. Photo by Robert Reigh

Figure 3. Incomplete closure of the umbilical opening will produce a scar on the belly skin at harvest. Photo by Millie Williams