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Author Topic: Conch Eggs  (Read 8209 times)
Soldier
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« on: June 28, 2008, 09:45:47 PM »

The Conchs in my SW tank have started putting these small white things all over the tank in groups of 10-30. Each one is about a quarter to a half inch in length and about as skinny as a pen tip. These are eggs right? How long to they take to hatch? This started about 2 weeks ago. The first batch that they laid is starting to get a darker color, so does that mean their is something growing or are they just getting old?
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« Reply #1 on: June 30, 2008, 01:14:21 AM »

FIRST REPORTED CAPTIVE SPAWNING OF THE QUEEN CONCH, STROMBUS GIGAS

Research Team:
Megan Davis (HBOI) - Principle Investigator
Amber Shawl (HBOI)
Jerry Corsaut (HBOI)

In the first reported event of its kind, researchers from Harbor Branch Oceanographic Institution's Aquaculture Division have determined that female queen conch (Strombus gigas) can lay egg masses in captivity. The spontaneous spawning event was recently documented in rearing tanks that communally house queen conch along with three other conch species (Florida fighting conch Strombus alatus, milk conch S. costatus, and hawkwing conch S. raninus ). These animals are part of a recently initiated HBOI conch research project aimed at designing methods leading to commercial cultivation of alternative species to the queen conch, a popular fisheries species that has been the subject of mariculture efforts since wild populations began to decline in the 1970s.

For several years, Dr. Megan Davis - Director of Harbor Branch Aquaculture's ACTED aquaculture education program and head of the Harbor Branch conch project group, has conducted research on improving the culture techniques of conch in Florida and the Caribbean. This is the first time that Dr. Davis has not had to resort to collecting queen conch eggs from the wild. Captive spawning of other conch species occurs readily under appropriate rearing conditions. Although they attain a smaller adult size than queen conch, captive spawning success in other conch species made it likely that culture of one or more of these alternate species would eventually fill some market niches initially developed for queen conch. But the knowledge that queen conch also now appear capable of reproducing under culture conditions may change that.

"This event is exciting," notes Dr. Davis, "because it strongly suggests that we will be able to close the cultured life cycle of the queen conch, and end our reliance on natural sources of eggs."

Successfully growing animals "from egg to entree" - and through successive generations - is the goal of closed-cycle aquaculture. And it is a particularly important research plateau to reach in the case of the queen conch, because eggs and larvae spawned in one geographical location very often are the animals that ultimately recruit (settle) to new locations, sometimes a hundred or more miles away. It is known that overfishing of adult conch in a location that serves as a larval source pool may have negative implications for recruitment success within larger and/or more distant settlement locations.

To a much smaller extent, conch hatchery operations can contribute to the same problem. If a hatchery must always resort to wild egg collection then they are not necessarily just robbing the cradle in terms of local recruitment success - they may be negatively affecting recruitment success over a much larger geographical region as well. Closing the queen conch culture cycle will guarantee that success of the aquaculture operation does not occur at the expense of already impoverished wild stocks.

Dr. Davis and research assistant Jerry Corsaut believe the fact that the successfully spawning queen conch were housed communally with actively mating individuals of other conch species may well have been instrumental in triggering the queen conch to mate and spawn. The species are physically isolated from one another by means of partitions, but waterborne pheromones or other chemical spawning cues may have been transmitted by one conch species and picked up by neighboring queen conch.

Most importantly, the laying of the egg mass was not a one-time event. The same female queen conch has produced four separate masses so far, on February 12, February 21, March 4, and March 11. As of the time of this writing (March 15), approximately 2,000 animals emerging from the first egg mass have been successfully brought through an 18-day larval rearing period and have metamorphosed to benthic post larvae. Animals from the second egg mass are currently 6-lobed planktonic larvae that have spent 16 days in the water column, while those from the third clutch hatched out earlier this week. Larval queen conch from the most recent egg mass are due to hatch out within a couple of days.

NATURAL STOCK DECLINES AND AQUACULTURE RESEARCH ACTIVITIES

No visit to Key West, Florida - capitol of the Conch Republic - would be complete without savoring a plate of conch fritters or a bowl of conch chowder from one of the local dining establishments.

But for more than 25 years, the delicious conch consumed in Key West - and everywhere else in the US - has had to be imported from neighboring Bahamas and various Caribbean countries. That's because the Florida commercial and sport conch fisheries had completely collapsed by the mid 1970s, primarily due to overharvest. Commercial harvest of queen conch in the Keys was banned in 1975, and a ban on all commercial and recreational harvest of the species was enacted in 1986.

The queen conch (Strombus gigas) is a large marine gastropod mollusc native to the shallow seagrass and near-reef habitats of Florida, the Bahamas, the Caribbean Islands, Bermuda and the coast of Central and South America. Although it has been the basis of local subsistence fisheries for centuries, queen conch populations are in decline throughout their range - unable to keep pace with growing pressure of commercial harvest. The animal is slow to mature, taking three years and more to grow to harvest size in the wild. Add to that the development of improved diving equipment, and some of the causes underlying the collapse of the US conch fishery become clear.

Though still showing signs of overharvest, queen conch populations in the Bahamas and some Caribbean countries are in somewhat better shape, partly due to restrictions which prohibit the use of scuba gear by conch fishermen. This allows the survival of small, deepwater "refuge" populations even as shallow conspecifics are harvested en masse - ensuring at least some reproduction to replenish the regional stocks. Nonetheless, continued strong export demand and the widespread adoption of freezer storage and refrigerated transport in the 1970s have contributed to the decline of queen conch populations throughout their natural range.

The inevitable decline in wild queen conch stocks was foreseen by biologists, and as far back as the 1970s, individuals from the aquaculture industry began exploring captive culture strategies to meet increased product demand and ease pressure on overburdened wild populations. The first attempts at commercial conch culture were carried out at the Caicos Conch Farm, established in 1984 in the Turks and Caicos Islands. The farm is still in operation; in addition to pursuing commercial viability of conch production for human consumption, the farm hopes to begin a program to release hatchery-produced juveniles to the wild to augment dwindling local populations.

Today, Caicos Conch Farm has 3 million queen conch at various developmental stages in it's inventory. The farm's goal is to produce 1.5 million conch per year to add to their inventory. Each week, the farm prepares 1,000-2,000 lbs of live product to be shipped to specialty "white table restaurant" markets in Florida. Several restaurants on Providenciales (the island on which Caicos Conch Farm is located, called "Provo" by the island's residents) also feature farm-raised conch on their menu.

Conch aquaculture research and public education is also underway in the Aquaculture Division of Harbor Branch Oceanographic Institution, at a university research facility in Merida, Mexico, and at three facilities in the Florida Keys.

The Florida Straits Conch Company opened in Key West in 1999. It features a restaurant highlighting dishes prepared using farmed-raised conch. Also on site is the Conch Farm Educational and Research Foundation - a museum complex housing exhibits intended to inform visitors of the conch's history in the Keys. The museum includes a mini-conch farm demonstrating strategies for raising the animal from egg to adult.

A stock rehabilitation hatchery operated by the US Fish and Wildlife Conservation Commission began operating in 1991 at the Keys Marine Laboratory on Long Key, Florida. The hatchery is run by Bob Glazer of the Florida Department of Environmental Protection's Florida Marine Research Institute. The rehabilitation hatchery is the facility that provided Megan Davis' Harbor Branch conch project with the stocks that include the first queen conch to successfully spawn and lay egg masses in captivity. These brood animals were initially collected as egg masses from Florida Bay but have grown to maturity in captivity, first at the Long Key research facility and then at Harbor Branch.

The Long Key rehabilitation hatchery is primarily concerned with elucidating the most effective strategies for captive-rearing queen conch and releasing them to the wild. They have engaged in studies aimed at determining the optimum release size, release season, and the best lunar phase (i.e., full moon or new moon) under which to release animals.

The Keys Marine Conservancy, on Plantation Key, is a recently started non profit organization actively seeking support to develop an education and conservation facility to restock overfished or otherwise diminished native species in the Florida Keys, including queen conch, long-spined sea urchins, spiny lobsters, and various species of corals and sponges.

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.
 
 
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