The live bait shrimp industry in the southeastern U.S. is dependent on three shrimp species: the Atlantic white shrimp (Litopenaeus setiferus), the Gulf brown shrimp (Farfantepenaeus aztecus) and the Gulf pink shrimp (F. duorarum).
All three species occur along the southern and eastern U.S. coasts from Texas through North Carolina.
The live bait shrimp industry within this extensive coastal region is mostly a capture fishery. Juvenile shrimp within a size range of 150- to 60-count shrimp (3.0- to 7.5-g) are harvested from inshore waters with trawling gear.
Recently, farm-raised, live bait shrimp were introduced as an alternative to wild-caught shrimp.
Bait shrimp market:
The wild product is highly seasonal and the supply rarely meets demand, especially during the peak demand period of March through September. Shrimp are sold as both a live and a frozen product, with live shrimp commanding a premium price.
The dockside (ex-vessel) price wholesalers pay to boat captains for live bait shrimp ranges from $2.75 to $4.00 per pound. The wholesale price bait retailers pay ranges from $7.50 to $14.00 per pound. This wholesale price includes delivery from the shrimp boat to the retail bait shop and so it varies with the distances involved.
Retailers who own their own shrimp boats may charge fishermen as little as $7.00 per pound; in general, fishermen pay $10 to $16 per pound for live bait shrimp (Fig. 1).
Live hauling bait shrimp:
Wild-caught bait shrimp are transported to market in oxygenated holding tanks at densities of 1 to 2 pounds per gallon of water. Mortality rates can be 25 to 50 percent within 24 hours of delivery.
However, live-haul trials of farm raised, live bait shrimp showed that commercial volumes (200 to 500 pounds per shipment) could be successfully transported to retail bait shops with more than 95 percent survival 24 hours after delivery.
The main impediment to bait shrimp aquaculture has been the lack of consistent supplies of disease- free postlarvae (PL). Without them, both researchers and commercial aquaculturists have relied on two methods of obtaining PL.
Method I – sourcing wild, mated, gravid females:
This method entails leasing coastal shrimp boats during the full moons of spring and early summer to trawl the spawning grounds for mated, gravid (egg-bearing) females. Once gravid females are caught, they are either spawned in individual tanks onboard the vessel or transported to land-based spawning tanks.
Each gravid female is kept in an individual tank for 12 to 36 hours under dark conditions, at a temperature of about 28 °C (82.4 °F), and at a salinity of 30 to 35 ppt. After spawning, the female is removed from the tank and the fertilized eggs hatch within 24 hours.
Sourcing wild, mated, gravid females is a cost-effective technique for acquiring fertilized eggs, but it is not a reliable year-round production method. There also is a high risk of acquiring shrimp infected with viral pathogens that will jeopardize the biosecurity and sustainability of the farm.
Method II– hatchery:
Developing and operating a biosecure hatchery is both capital and labor intensive. However, a biosecure hatchery ensures a sufficient year-round supply of PL for commercial operations. Healthy broodstock must be developed and maintained in a disease-free hatchery.
The quantity of viral pathogen-free broodstock is limited. Researchers at the Mote Marine Laboratory in Sarasota, Florida, the Waddell Mariculture Center in Bluffton, South Carolina, and the Texas Agricultural Experiment Station in Corpus Christi, Texas, are isolating and developing “high- health” broodstock populations of the Atlantic white shrimp and Gulf pink shrimp.
“High-health” broodstock are developed through a process of quarantine and routine population testing using histological examination and a polymerase chain reaction (PCR) technique. Continuous screening of broodstock and offspring with these diagnostic tools detects organisms with specific pathogens so they can be eliminated from these populations.
Once a “highhealth” wild population has been isolated, it is induced to spawn and its offspring are tested for known viral pathogens. Once the offspring are determined to be “clean,” they are moved to a biosecure grow-out facility where they are raised to broodstock size.
The broodstock are then reproduced in maturation facilities and their offspring are used to supply farmers with PL. The maturation and reproduction of broodstock occur in a climate controlled maturation system (27 °C, 80.6 °F) with 14-hour light and 10-hour dark photoperiods (Fig. 3). Broodstock are kept in 10.5- to 16.4-m2 (12-ft to 15-ft diameter) maturation tanks at densities of six shrimp per m2.
During maturation, broodstock are supplied with a combination of fresh squid, adult enriched Artemia and bloodworms fed on a wet-weight basis (20 percent of body weight per day, bw/d). Dry maturation diets are added to reduce the cost of fresh food. Once acclimated to the maturation system, females are unilaterally ablated—a process in which one eyestalk is removed to induce maturation.
Ovarian development ensues within 72 hours and mating and spawning begin thereafter. Broodstock ranging from 25 to 35 g have a reproductive capacity of 100,000 to 250,000 eggs per spawn and can spawn every 3 to 7 days. Fertilized eggs will hatch within 24 hours of fertilization at 28 °C (82.4 °F).
The nauplii are allowed to remain in hatching tanks until they metamorphose into the last naupliar stage (N5). During the naupliar stages, no feed is provided as nauplii feed on their yolk sacs.
Nauplii (N5) are then collected and transferred to larval-rearing tanks maintained at 28 to 29 °C (82.4 to 84.2 °F) where they are fed marine algae (Chaetoceros gracilis and Isochrysis galbana), live, newly hatched Artemia nauplii, and dry larval and postlarval diets, depending on the stage of development and the dietary needs of that stage.
Shrimp larvae go through six larval stages over a 9-day period in the larval-rearing tank before they metamorphose to a postlarval (PL1) stage. The entire larval cycle from N5until the shipment of the PL8-13 lasts 17 to 22 days, depending on the age of the PL requested by the farm. In general, farmers request PL8- PL13for stocking production systems.
Ryan L. Gandy