TRADITIONAL CONCH CULTURE METHODS

Captive conch production traditionally relies on obtaining seed stock from the wild - either from free-ranging animals or from adult animals collected and enclosed within a so-called "egg farm". Seed stock is collected in the form of conch egg masses, laid between March and September when adult conch populations form large spawning aggregations within shallow seagrass and sandflat habitats. Egg masses (each containing up to one-half million eggs) are transported to hatchery facilities, where planktonic conch larvae hatch from the eggs in 3-5 days. Conch larvae will spend the next 21 days living and feeding within the water columns of artificial rearing units.

Feeding the planktonic conch larvae - called "veligers" - represents a considerable challenge to aquaculturists. They must be provided with appreciable quantities of a live microalgal diet which itself must be painstakingly grown by aquaculture technicians. The Harbor Branch conch project group feeds their larval conch a specific strain of the microalga Isochrisis galbana, which must be provided at densities of from 5,000 to 30,000 cells/ml of culture water volume, depending on the size and culture density of the conch larvae. Culture water is pre-treated with UV irradiation to kill pathogenic organisms. Conch larvae are reared at a density of from 20 to 50/L. During the larval stage, conch veligers progress from a two-lobed, to a four-lobed, and ultimately a six-lobed form before they are ready for metamorphosis into the more familiar benthic (bottom-dwelling) juvenile stage.

Metamorphosis does not occur spontaneously. Rather, late-larval (six-lobed) conch will only progress to the benthic stage of their life history if an appropriate environmental settlement cue is present. In nature, this cue is typically a chemical or suite of chemicals produced by the various species of benthic microalgal diatoms that the juvenile conch will feed on after settlement. The requisite chemical settlement stimulus makes ecological sense; its presence in quantities detectable by settlement-age conch larvae indicates a habitat in which preferred food sources are abundant, and provides a strong inducement for the conch to take up residence as juveniles in a promising new environment.

In the past, Dr. Davis has utilized a variety of natural settlement cues to induce conch metamorphosis, including the benthic diatoms variously associated with seagrass blades, detritus, and sand collected from juvenile conch habitats. The Harbor Branch conch group also successfully utilize extracts from the red macroalga Laurencia (not a preferred food resource for juvenile queen conch) to induce settlement of 'metamorphically competent' (i.e., ready to become benthic postlarvae) conch larvae.

More recently, a researcher from the University of Delaware has discovered that hydrogen peroxide can be substituted as an artificial cue to induce settlement as well. When six-lobed conch exhibit morphological and/or behavioral signs that they have become competent to settle, Dr. Davis now adds hydrogen peroxide as an inducer; 75% of settlement-age conch veligers successfully metamorphose to postlarval stage within five hours of hydrogen peroxide addition.

Settled conch postlarvae, averaging just over 1 mm shell length, are stocked on small mesh screen trays at a density of 1,600/m2. Interestingly, they are reared in captivity on a diet of flocculated (artificially settled) planktonic microalgae (Chaetoceros gracilis), rather that on a benthic diatom diet that would more closely mimic the diet of wild counterparts. The existence of proven microalgal propagation techniques give rise to this seemingly odd variation on Nature's themes. At 5 mm shell length, juvenile conch are transferred to sand-filled trays and are fed a combination of ground artificial feed and Chaetoceros microalgae.

When the animals reach 12 mm shell length, they are moved to large concrete nursery ponds and provided with strong water circulation, a sand substrate, and a constant food source (a gel matrix consisting of the green macroalga Ulva and a specially formulated pelleted food) on which they graze throughout the day. Under such rearing conditions, individuals can grow approximately 0.3 mm/day. When animals reach a shell length of about 9 cm, they are typically placed into the natural environment, within a fence enclosed shallow seagrass/sandflat growout pasture.

The traditional queen conch market has been for adult animals (>16 cm shell length), consumed as food. A secondary consumer market exists based on sale of the beautiful shells of adult queen conch, although this market is often filled as a byproduct of conch harvest for food.

Novel markets for conch products are also beginning to emerge as a result of developing conch aquaculture programs. There is a demand by the marine aquarium trade for small (2.5 cm) tank-sized animals. There is also an effort to expand a niche market for 'ocean escargot' - those conch of approximately 6 cm shell length reared and sold for human consumption. Animals ranging from 7 to 9 cm are preferred for use in wild stock enhancement efforts because their relatively large size affords them at least a degree of protection from crabs, rays, turtles, octopi, and other would-be predators.

A CITES (Convention on International Trade in Endangered Species) permit is required to sell cultured or wild-harvested queen conch. This is meant to ensure that wild conch or their seed stock are harvested at levels consistent with local fisheries populations. But research focusing on a number of non restricted Strombus species (e.g., the hawkwing conch Strombus raninus, milk conch S. costatus, and the Florida fighting conch S. alatus) suggests that one or more of these may be suitable for culture as alternative conch species - at least for the smaller-sized (below 6 cm) animal markets.

CONCH AQUACULTURE EDUCATION RESOURCES FROM HBOI

The HARBOR BRANCH Division of Aquaculture's strong commitment to education and training is realized through the Aquaculture Center for Training, Education and Demonstration (ACTED). Harbor Branch launched the ACTED program in 1995, when the Florida State constitutional ban on net fishing created an immediate need for hands-on, practical training in aquaculture species and production systems. Since that time ACTED has grown to include a wide variety of workshops and short courses, the Associate in Science degree program in partnership with Indian River Community College, and a middle school and high school education program for students and their teachers. The Aquaculture Pavilion is used to educate visitors about aquaculture and ACTED has organized both large and small conferences and workshops.

The Harbor Branch ACTED Program has also just released a video entitled "The Conch's Life Story." This 5 minute video highlights reproductive biology, larval development, and juvenile stage development of cultured queen conch, and features superb videomicroscopy shot by award-winning HBOI videographer Brian Cousin. Production of the video was made possible by the support of HBOI and the Keys Marine Conservancy. Copies of the video can be purchased for $10.00 each.
Please contact ACTED Director Dr. Megan Davis to place orders.

Another Conch resource is at www.oakhammockbooks.com/conchnews.

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Cultured Conch Lifecycle - Quicktime 4 format - (1.0Mb) (exerpted from The Conch's Life Story)