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Black soldier fly (Hermetia illucens Linnaeus) as feed for the American alligator (Alligator mississippiensis Daudin).

ABSTRACT

Larvae of Hermetia illucens Linnaeus (Diptera: Stratiomyidae), the Black Soldier Fly (BSF), or one of two commercial feeds were offered to three randomized groups of hatchling American Alligators (Alligator mississippiensis Daudin) (Crocodylia: Alligatoridae) for three months and their growth monitored. Statistical analysis of weight (g) (Wilcoxon/Kruskal-Wallis Test) and snout-vent length (cm) (Welch ANOVA F-test) increases were significantly greater in groups of alligators fed 56% protein/11% fat or 45% protein/8% fat commercial feeds versus alligators fed BSF. Based on these results, BSF can not be recommended as a complete replacement for commercial feeds in young alligators.

Key words: Alligator mississippiensis, American Alligator, Black Soldier Fly (BSF), Hermetia illucens, nutrition.

INTRODUCTION

The black soldier fly (Hermetia illucens Linnaeus; Diptera: Stratiomyidae) (BSF) has been used as feedstuff for poultry (1), swine (2), fish (3, 4) and frogs (Shepard, unpublished). Larvae have been fed experimentally to these species as a partial replacement for soybean or fish meal in a formulated diet. BSF produced on animal manure or restaurant food waste have been valued as a $500/ton feedstuff comparable to Menhaden fish meal (3, 4). Fat and protein meal fractions can be readily separated by commercial rendering plants. Pre-pupal BSF are 44% dry matter and are composed of 42% protein and 35% fat, including essential amino and fatty acids (1).

American alligators (Alligator mississippiensis Daudin; Crocodylia: Alligatoridae) have been raised commercially in the south for many years. More than 295,000 were harvested in commercial operations in Louisiana in the 2004 tag year with a market value of over $33 million (5). The diet of wild alligators changes over time and is influenced by the size of the individual (6). Research on the diets of wild alligators indicates alligators consume a diet high in protein and low in fat (7). Artificial diets consist of approximately 45% crude protein and 8% fat for older animals, and 56% protein with 11% fat for hatchlings (<41 cm total length) and juveniles (<122 cm total length). The feeds are a blend of fish meal, meat and bone meal, blood meal, and some vegetable protein (7). The pelleted feeds are further fortified with vitamins and minerals (7). Commercial diets are relatively expensive due to the need for animal based protein. Some producers continue to feed a combination of meat (nutria [Myocastor coypus], beef, horse [Equus caballus], chicken [Gallus domesticus], muskrat [Ondatra zibethicus], fish, beaver [Castor canadensis], and deer [Odocoileus virginianus]) and commercial diets (7). Regardless if fed a blended diet or entirely commercial diet, feed conversion rates decrease as alligators grow larger, 40% or between 2:1 and 3:1, up to a length of 1.83 m. Intensively reared alligators can reach market size (1.22 m) in less than 2 years (7).

Wild juvenile alligators are primarily insectivorous (6). For this reason, as well as the expense of feeding commercial diets, we investigated the feasibility of BSF pre-pupae as a principle feed for hatchling alligators and determined if they would grow at comparable rates to control groups fed commercial alligator diets.

MATERIALS AND METHODS

BSF larvae reared on restaurant food waste were provided by The Venture Group (Lafayette, LA). Raised commercially, BSF larvae are self-harvesting at the time of pupation, crawling away from their contained food source and into strategically located containers allowing large quantities to be collected and processed. Pre-pupae were collected, spread in a shallow metal pan, and dried overnight at 50[degrees]C. Dried BSF were stored in plastic bags within an airtight metal canister at room temperature for the duration of the feeding trial.

Because alligators typically lay between 20-60 eggs, the 96 day-old hatchlings obtained in August 2003 were collected from as few clutches as possible by the Louisiana Department of Wildlife and Fisheries (Rockefeller Wildlife Refuge, Grand Chenier, LA). Juveniles were transported to Northwestern State University, Department of Biological Sciences in Natchitoches, LA where they were allowed to acclimate for 2 weeks prior to the feeding trial. Upon arrival, alligators were divided into three groups and randomly placed in pre-fabricated plastic tubs that provided approximately 0.14 [m.sup.2] per animal, in accordance with guidelines from the Southern Regional Aquaculture Center of 0.09 [m.sup.2] per animal until 0.61 m in length (7). The central portion of each enclosure was kept filled with municipal water and provided with exit ramps to the encircling basking areas. Mean daytime air temperature was 23[degrees] C and mean night air temperature was 21[degrees] C. Supplemental heat was provided by infrared heat lamps suspended above the enclosures. Water changes and cleansing were performed daily or every other day. The animals were kept entirely in the dark, except during feeding and maintenance, throughout the acclimation period and feeding trial as alligators are sensitive to light and sound (7). Darkness is thought to decrease intraspecific aggression and stress (Elsey, personal communication). Because it is known that alligators will consume a dry pelletized feed following absorption of their yolk sac, all alligators in this study were provided a commercial high protein diet ad libitum during the acclimation period to accustom them to a dry diet and insure all individuals were eating. Alligators were fed by placing the food on the basking areas. Alligators were fed five days a week, and all uneaten food was removed the following day.

Following the two week acclimation, alligators were randomly assigned to one of three dietary treatment groups, BSF (n=30), 45% protein/8% fat commercial diet (n=33) (Burris Mill & Feed, Inc., Franklinton, LA), or 56% protein/11% fat commercial diet (n=33) (Burris Mill & Feed, Inc., Franklinton, LA). There was no attempt to separate the animals by sex due to the extreme difficulty in animals of this size and in conformance with protocols found in commercial production facilities. Primary ingredients of the commercial feeds were fish meal, flash dried blood meal, corn gluten meal, hydrolyzed feather meal, dehulled soybean meal, ground corn, wheat middlings and stabilized animal fat. At the onset of the feeding trial, all alligators were weighed and snout-vent length (SVL) determined. Food quantity was initially calculated on 2% of the mean group body weight/day, then as 5% mean group body weight/month, so that there was always an excess of food provided. As previously, commercial feed or BSF was placed on the basking areas five days a week following cleaning of the enclosures. Animals were measured and weighed monthly for 3 months.

Statistical analysis was performed on the degree of variability of weight and length using the general linear model with repeated variables procedure via JMP IN 4.0.3 software (SAS Institute Inc., Cary, NC). Analyzing the weight change by treatment group data indicated that the set was non-normal necessitating the use of nonparametric procedures to adjust for this non-normality. Final analysis utilized the Wilcoxon/Kruskal-Wallis (Rank Sums) Test for comparison of weight gain between treatment groups and the Welch ANOVA F-test for comparison of length between treatment groups.

At the conclusion of the study the alligators were returned to the Department of Wildlife and Fisheries, Grand Chenier, LA.

RESULTS AND DISCUSSION

Alligators benefit from being fed a more nutritionally complete feed, such as a nutria or chicken based diet, rather than fish based (8). Because hatchlings and juveniles are primarily insectivores, we assumed that BSF would be an appropriate substitution for fish meal based diets.

Mean SVL increases and weight gains over the 3-month study for the three treatment groups are presented in Table I. Median SVL, SVL ranges, median weight, and median weight ranges are presented in Table II. All groups as a whole increased in length and weight. However, growth was not consistent between individuals in each group (Table II) and did not represent a normal distribution for weight while the residuals found from fitting length change by treatment group were approximately normal. The Wilcoxon/Kruskal-Wallis (Rank Sums) Test for weight change by treatment group indicates that there was a significant difference among means (p = 0.0026). Tests for unequal variance in length revealed that there were unequal variances among treatment groups (Levene, p < 0.0001; Bartlett, p < 0.0001; Brown-Forsythe, p < 0.0001). Therefore, the Welch ANOVA F-test was used to compare lengths and indicated a significant difference between the means (p = 0.0175).

The disparity in growth skewed the data sets, and likely occurred for a number of reasons. Male and female alligators grow at different rates (Elsey, personal communication). It is possible a more binomial distribution was beginning to develop based on sex, and would have been more apparent if the duration of the feeding trial were longer. With a longer feeding trial resulting in larger animals, sex determination becomes much easier and less likely to result in misidentification of gender. Temperature also influences growth, and constant temperatures of 30[degrees]-31[degrees] C or greater are recommended for grow-out operations (7). This recommendation is higher than the mean of our day and night temperatures. Since all alligators were housed in the same room within the facility under identical conditions, we would expect a reduced growth rate but not to the extent observed and it should have affected all equally. Stress, due to disturbance during cleaning and feeding may also have contributed to the growth patterns observed.

Palatability and size of the food items are the most likely explanation for the differences noted in size and weight. Alligators were observed to begin feeding on the commercial diets immediately upon its placement on the basking areas of the enclosures. Commercial pellets are round and approximately 6.4 mm in diameter while dried BSF are 25 mm in length, 6 mm in width, and rather flattened. Pellets appeared to be easier for the hatchlings to grasp. It was rare to see alligators feed upon the BSF. Little of the commercial feeds remained when enclosures were cleaned the next day, while large quantities of BSF were always present. Our conjecture is that had they fed on BSF in amounts equal to commercial feed, they would have grown as much or surpassed in growth those eating commercial feed. Interestingly enough, although it was not possible to collect and weigh food remains to validate this conjecture due to pellets being knocked into the water and dispersing, it seems as if conversion of BSF was as good as or better than conversion of commercial feed, based on SVL and weight gains versus quantity of food placed in enclosures (data not reported).

Because of the significant differences in feed efficiency trends noted during the 3-month feeding trial, we can not recommend dried BSF alone as a replacement for commercial feed for hatchling alligators based on the trends observed. The results demonstrate that dried BSF are sufficient to promote growth, but in an unprocessed form, are inferior to commercial feed. However, this experiment was preliminary and did not address key variables such as movement (live BSF versus dried), shape, palatability or feed conversion, which would be necessary to definitively conclude that BSF is not an equal or superior food source for hatchling alligators. Further work is necessary to evaluate the possible use of BSF as a feed supplement or as the total source of protein in commercially milled diets.

ACKNOWLEDGEMENTS

This project was supported by a Nutrition Research Grant from Central Nebraska Packing, Inc., North Platte, NE. The authors also wish to thank Dr. Andre Blanchard of The Venture Group for supplying the BSF larvae and Dr. Ruth Elsey of the Rockefeller Wildlife Refuge for providing the alligators.

REFERENCES

1. Hale OM: Dried Hermetia illucens larvae (Diptera: Stratiomyidae) as a feed additive for poultry. J Georgia Entomol Soc 8: 16-20, 1973.

2. Newton GL, Booram CV, Barker RW and Hale OM: Dried Hermetia illucens larvae meal as a supplement for swine. J Anim Sci 44: 395-400, 1977.

3. Bondari K and Shepard DC: Soldier fly larvae as feed in commercial fish production. Aquaculture 24: 103, 1981.

4. Bondari K and Shepard DC: Soldier fly, Hermetia illucens L., larvae as feed for channel catfish, Ictalurus punctatus (Rafinesque), and blue tilapia, Oreochromis aureus (Steindachner). Aquaculture and Fisheries Management 18: 209-220, 1987.

5. Louisiana Department of Wildlife and Fisheries, Fur and Refuge Division. Louisiana's Alligator Management Program Gator Notes 1(3) (July-October), November 2005.

6. Delany MF: Late summer diet of juvenile American Alligators. J. Herpetology 24: 418-421, 1990.

7. Masser MP: Alligator Production. Grow Out and Harvest. Southeast Regional Aquaculture Center Publication No 232, 4 pp, 1993.

8. Joanen T and McNease L: Alligator farming research in Louisiana, USA. In Wildlife Management: Crocodiles and Alligators (Webb, Manalis and Whitehead, Eds) New South Wales, Australia: Surrey Beaty and Sons, pp 329-340, 1987.

Michael S. Bodri, MS, VMD, PhD

Department of Biology

North Georgia College & State University

Dahlonega, GA 30597

and

Elizabeth R. Cole

Department of Mathematics

Northwestern State University

Natchitoches, LA 71497

Work performed at Northwestern State University, Natchitoches, LA 71497

Address correspondence to: Michael Bodri, Department of Biology, North Georgia College & State University, Dahlonega, GA 30597.

706-864-1958. MSBodri@ngcsu.edu.
Table I. Mean and SD for snout-vent length (SVL) (cm) and weight (g)
increases in hatchling American alligators (Alligator mississippiensis
Daudin) fed either dried black soldier fly (BSF) pre-pupae (Hermetia
illucens Linnaeus) or commercial diets of 56% or 45% fish-based protein
over a 3-month period. Welch ANOVA F-test indicates a significant
difference among means for length (p=0.0175). Wilcoxon/Kruskal-Wallis
(Rank Sums) Test indicates a significant difference among means for
weight (p=0.0026).

 DAY 0 DAY 28
DIET SVL (cm) Wt (g) SVL (cm)

BSF 12.02[+ or -]0.52 49.99[+ or -]4.98 12.87[+ or -]0.76
56% Protein 11.96[+ or -]0.57 49.20[+ or -]5.35 12.45[+ or -]0.83
45% Protein 11.98[+ or -]0.42 48.65[+ or -]5.36 12.61[+ or -]0.62

 DAY 28 DAY 56
DIET Wt (g) SVL (cm) Wt (g)

BSF 52.51[+ or -]7.92 13.51[+ or -]0.77 58.42[+ or -]9.31
56% Protein 55.51[+ or -]15.79 13.81[+ or -]1.71 78.81[+ or -]34.44
45% Protein 52.83[+ or -]12.63 13.72[+ or -]1.45 69.76[+ or -]28.63

 DAY 84
DIET SVL (cm) Wt (g)

BSF 13.86[+ or -]0.87 59.16[+ or -]10.43
56% Protein 14.82[+ or -]2.17 106.05[+ or -]53.21
45% Protein 14.60[+ or -]2.06 93.16[+ or -]48.48

Table II. Median snout-vent length (SVL) and weight (g) increases, and
ranges, in hatchling American alligators (Alligator mississippiensis
Daudin) fed either dried black soldier fly (BSF) pre-pupae (Hermetia
illucens Linnaeus) or commercial diets of 56% or 45% fish-based protein
over a 3-month period.

 DAY 0 DAY 28
DIET PARAMETER SVL (cm) Wt (g) SVL (cm) Wt (g)

BSF Median 12.1 50.7 12.8 51.2
 Range 10.4-13.1 39.6-59.0 11.3-14.2 40.5-71.7
56% Protein Median 12.1 48.9 12.3 49.4
 Range 10.2-13.2 38.4-59.5 10.5-13.8 34.5-89.1
45% Protein Median 11.9 49.9 12.5 50.5
 Range 11.2-12.9 39.1-57.3 11.3-13.4 36.3-83.5

 DAY 56 DAY 84
DIET PARAMETER SVL (cm) Wt (g) SVL (cm) Wt (g)

BSF Median 13.65 57.2 13.8 59.0
 Range 11.6-14.9 41.2-83.4 11.8-15.7 39.1-85.9
56% Protein Median 13.7 76.6 15.0 109.3
 Range 11.2-16.4 34.2-145.8 11.5-18.4 35.8-210.4
45% Protein Median 13.1 65.0 14.3 93.1
 Range 11.6-16.6 35.3-131.4 11.4-18.1 33.6-181.2
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Author:Bodri, Michael S.; Cole, Elizabeth R.
Publication:Georgia Journal of Science
Article Type:Report
Geographic Code:1USA
Date:Jun 22, 2007
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