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| Current Sturgeon Restoration Research
1. Feed training of wild-caught Atlantic sturgeon
Developing captive broodstock populations for stock enhancement purposes in areas where sturgeon populations are extirpated is a potential restoration strategy. A key challenge in establishing a captive broodstock of wild-caught sturgeon is training fish to eat commercial pellets. Captured wild fish do not readily accept commercial diets, or in some cases, even natural foods, often resulting in excessive weight loss, reduction in fish condition factor, and mortality.
We evaluated various feeding methods to train wild-caught sturgeon from the Chesapeake Bay (via a reward program administered by the Maryland Department of Natural Resources and US fish and Wildlife Service) onto a commercial pelleted diet. Sturgeon held in flow-though (Choptank River water) tanks were fed by either weekly force feeding, where a tube was inserted into the sturgeon’s alimentary tract and a natural food slurry was injected or daily passive feeding, where sturgeon were offered pieces of natural food (bloodworms, clams, shrimp, and squid) directly. Both methods were successful in training sturgeon; however, force feeding is excessively stressful to the fish and unnecessary due to the success achieved with various passive feeding regimes. Sturgeon were offered varied ratios of natural and commercial pellets in several forms (dough balls and gel diets) to transition them to a diet consisting entirely of commercial pellets. |
Sturgeon are weighed monthly to track weight gain.
Example of one successful diet regime beginning with shrimp; followed by a gelatin diet consisting of shrimp, fish, various vegetables, and ground commercial diets; and lastly the commercial diet.
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We successfully trained 92% of smaller fish (< 10 kg) and 35% of large fish (>10 kg) to eat commercial pellets. Most of the remaining large fish have accepted natural foods and a combination diet, except for two large fish that were released at their capture location because they did not accept the commercial diet and experienced excessive weight loss. Average weight gain during the study ranged from -27% to 160%. Sturgeon began eating commercial pellets 3 to 39 weeks after initial feeding, depending on fish size, feeding regime, and individual acceptance. Average time for acceptance of commercial diet for the better diet regimes was 9 weeks.
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2. Larval Live Food Enrichment Study
The use of automatic live food delivery and improved diets has led to advancements in hatchery success for Atlantic sturgeon. These advancements are especially important in restoration efforts because of the rarity of spawning females and thus of fry. However, the transition from live brine shrimp to commercial diets is a critical stage in larval sturgeon culture and is the period in which the greatest mortality occurs. Research has shown that enrichment of brine shrimp by certain fatty acids (DHA, EPA and ARA) for larval culture of several marine fish species significantly increases fry survival. We evaluated whether enriching live brine shrimp affects growth and survival of Atlantic sturgeon fry.
Enrichment treatment included a control (unenriched newly hatched brine shrimp nauplii), and three commercial algal based enrichments: 10% DHA, 10% DHA and astaxanthin, and 2% ARA. The process involved holding newly hatched brine shrimp in a brine solution with the dissolved enrichment substance 12 hours before feeding. Brine shrimp nauplii were delivered to tanks by an automatic bellows pump delivery system every 30 minutes.
There were no significant differences between the average weight of fry fed the unenriched diet and two of the enriched diets, suggesting that enrichment of brine shrimp is not necessary for optimal growth of Atlantic sturgeon fry. Fry survival ranged from 80 to 89.6%.
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Enrichment study with automatic brine shrimp feeding system; sturgeon larvae and brine shrimp nauplii; and sturgeon fry at end of study after weaning onto an artificial diet.
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3. Laproscopic sex determination
Identifying the sex of sturgeon is an important step in developing a captive broodstock population. The process is difficult because there are no external features to indicate the sex of a sturgeon, so an internal examination of the gonad is necessary. The traditional technique involves making a small incision in an anesthetized fish and visually inspecting the gonad to determine if it is either ovary or testes. Non-invasive technologies such as ultrasound have been unreliable to date. In cooperation with partners, Maryland Department of Natural Resources and US Fish and Wildlife Service, we evaluated laproscopy, a more advanced method of visual inspection to identify sex. Fish are anesthetized and the laproscope is into inserted into the abdominal cavity through a very small incision. Organ images that can be viewed on a monitor are easier to distinguish using the laproscope and the process can be done quickly to minimize stress to the fish. Another probe can be inserted to take a sample of tissue to verify type if necessary. The incision is sutured and can be treated with a topical antiseptic, with fish then placed in a recovery tank. The technique has been very successful and provides greater ability to identify sex compared to earlier methods. |
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