sign in sign up
<<
Home , Conch, Fasciolaria tulipa, Octopus, Permit (fish), Shellfish, Strombidae

SRAC Publication No. 7203

October 2005

Species Profile Queen , gigas

Megan Davis*

The queen conch, Strombus gigas, Natural history This movement is thought to help is the largest molluscan gastropod the conch make a quick escape (shell length, SL, of 7 to 9 inches; The adult of this slow-moving from predators and also break up 18 to 23 cm) of the six conch mollusc has a heavy shell (5 its scent trail. The eyes are highly found in the shallow - pounds; 2.3 kg) with spines on developed and are at the tips of grass beds of Florida, the each whorl of the and a two protruding stalks. At the base Bahamas, Bermuda, the glossy, deep pink, flared aperture of the eye stalks is a long pro- Islands, and the north- (Fig. 1). The orange-yellow man- boscis used for grazing diatoms ern coasts of Central and South tle, located around the soft body and detritus from blades America. The queen conch is of the conch, secretes the shell. and grains. The hardened tip (the ) found in the territorial waters of Adult conch have separate sexes at least 36 countries and depen- at the end of the single, black- speckled foot propels the conch (Fig. 2) and are sexually mature at dent territories. It is known by about 4 years, after the has various names, such as caracol forward in a “hopping” motion referred to as a strombid leap. fully flared (Fig. 1). Conch are (, Honduras, Columbia), found at a 1:1 sex ratio in carrucho (), cobo unfished populations. Queen (Cuba), and lambi (Hispaniola, conch form large spawning aggre- French Antilles). gations. Fertilization is internal. Many studies have focused on The typical 6- to 8-month egg-lay- management, ecology ing season is March to October, and culture techniques of S. with most activity occurring from gigas. In the mid-1970s, cultur- July to September when water ists began growing queen conch temperatures are the warmest (82 larvae to the juvenile stage for to 86 °F; 28 to 30 °C). The female stock enhancement and for grow- lays an average of nine egg mass- out markets as a way to offset es per season; each crescent- pressure. The same cul- shaped egg mass contains approxi- ture techniques have been used mately 400,000 eggs (Fig. 3). The to study larval ecology and - thin, sticky strand of eggs is cov- eries oceanography, which con- ered with sand grains to camou- tribute to the development of flage it from predators during the regional fisheries management 3- to 4-day incubation period. plans. After the eggs hatch, the plank- totrophic veligers (larvae) drift in the water column for 2 to 8 Figure 1. Shell of an adult queen weeks, depending on phytoplank- conch, S. gigas (7 to 9 inches; 18 ton concentration, temperature, *Harbor Branch Oceanographic Institution, to 23 cm SL). (photograph by Tom and the proximity of settlement Division, Ft. Pierce, Florida. Smoyer) . When the veligers are morphologically and physiologi- cally ready, they metamorphose into benthic in response to trophic cues from their sea- grass juvenile habitat. Most conch nursery grounds are in seagrass meadows less than 20 feet (6 m) deep, where the sea- grass density is 56 to 84 Thalassia shoots per square foot (600 to 900/m2). Juveniles have also been found in algal flats and on deep banks. The juveniles remain buried for most of their first year. As herbivorous gastropods, juve- niles and adults feed on a variety of such as the green sea- weed Batophora oerstedi, or on detritus or diatoms commonly associated with the seagrass . During the Figure 2. External sex organs of Strombus costatus (a) male and (b) female first couple of years, the juvenile milk conch, which are similar to those of S. gigas. (photograph by Tom conch grow longer shells (Fig. 4) Smoyer) and remain in the seagrass beds. Juveniles do not have flared lips and are sometimes referred to as rollers. As the flaring lip (Fig. 4) begins to form, the sub-adult conch migrate to deeper water near the reef tract and form spawning aggregations. Queen conch are estimated to have a life span of 25 years. Old conch have thick lips and are often called samba conch (Fig. 4). Fisheries and regulations For hundreds of years, queen conch have been harvested as a subsistence source and the shells used for ship ballast, tribal tools, building materials, jewelry and decoration. Beginning in the 1970s, the queen conch commer- cial developed in response to the rapid growth of in the Caribbean and the increased international demand for the . Dishes such as conch frit- Figure 3. Queen conch, S. gigas, egg mass. (photograph by LeRoy Creswell) ters, and salad are spe- cialties on menus throughout the region. Queen conch is consid- ered one of the most important weight of the , ranging range from $6.00 to $15.00 per benthic fisheries, second only to from 0.19 to 0.5 pounds (85 to pound and continue to increase spiny . 228 g). The receives as conch stocks become more $1.00 to $3.00 per conch as a threatened. Shells, which are a Conch are typically fished using wholesale price. The conch meat by-product of the meat market, snorkel gear. Once landed on the is processed to remove the thick are sold as curios and boat, the shells are removed and skin and the white meat is pack- in the U.S., and the discarded onto shell piles called aged and frozen in 5-pound (2.3- Caribbean for $5.00 to $20.00 “middens.” The conch meat is kg) boxes. Retail prices for conch each. about 7 to 8 percent of the total the , and USAID in ). In 1984, the first commercial conch farm was established in the Turks and Caicos Islands. Today, queen conch laboratories in Mexico (e.g., CINVESTAV-IPN) and Florida (e.g., Florida Fish and Wildlife Conservation Commis- sion, Harbor Branch Oceano- graphic Institution, and Mote Marine Laboratories) are con- ducting conch research and edu- cation programs. Culture techniques Broodstock and egg mass procurement Hatcheries must gather egg mass- Figure 4. Juvenile and adult S. gigas shells from 1 month old to 25 years old. es from the wild, which can be (photograph by Kathy Orr) an unreliable source. Therefore, an enclosed breeding site or “egg farm” is used to ensure a steady supply of wild egg masses for the The is the largest degradation may also be a factor, hatchery. A suitable egg farm site importer of conch from the especially the loss of important Caribbean and, in fact, imports nursery close to shore. • is or was traditionally inhabit- approximately 78 percent of the In 1992, queen conch was listed ed by adult conch, conch meat in the international in CITES Appendix II and • has a calcareous sand and trade. About 1 million pounds became the first large-scale fish- coral rubble substrate with (458,000 kg) was imported in eries product to be regulated by low organic content, 2004, mostly from the Turks and CITES. All conch shipments Caicos Islands (Trade Database: must be accompanied by a • is located where water move- www.cites.org). Imports were as CITES permit stating that the ment is less than 1 knot, high as 4 to 5 million pounds in exporting country has deter- • is 4 to 8 m deep, and 2002 and 2003 when Honduras mined that the specimens have • is within 3 km of the hatchery and con- been legally acquired and that facility, for ease of access and tributed more than 50 percent of the trade is sustainable. security. the supply to the U.S. In 2003, Some locations, including the CITES (Convention for the To retain the adult conch, the Bahamas, Puerto Rico and egg farm is enclosed with a rigid, International Trade of Endangered Florida, have established no-fish- Species of Wild Fauna and Flora) black polyethylene mesh (2 x ing zones or marine protected 2 inches; 5 x 5 cm) fence 1.6 to mandated a temporary closure of areas (MPA) to help conserve the the fisheries in these countries 3.3 feet (0.5 to 1.0 m) high. The queen conch and other ecologi- mesh is held perpendicular to until the stocks increase and a cally important species. These sustainable fisheries plan is put the substrate with reinforcing types of management efforts, rods and the ends are attached to into place. This multilateral envi- along with regional fisheries ronmental organization protects moorings, boulders or the land. It plans and enforcement, will help is not necessary to remove the and regulates species to ensure this important species recover. that international commercial fence during the nonbreeding trade does not threaten their sur- There is considerable interest in season unless it is in an area vival in the wild. the culture of the queen conch to where winter storms would dam- supplement dwindling natural age it. The depletion of conch stocks has populations. Research began in The egg farm should be stocked necessitated management regula- the 1970s in Los Roques, tions such as total fisheries clo- annually with sexually mature Venezuela, and in the 1980s sev- conch 1 month before the breed- sures (e.g., in Florida since 1986), eral labs in the region made sig- annual quotas, size regulations, ing season at a sex ratio of 1:1 nificant contributions to queen and a density of one conch per and the prohibition of scuba div- conch culture (e.g., University of ing. While overfishing is the pri- 100 square feet (one conch/10 Puerto Rico, University of m2). Conch are transported to the mary cause of the decline, habitat Miami, Foundation for PRIDE in egg farm under wet burlap bags (female in front, male behind) or ratories by placing each egg mass and can be held out of the water observe females laying egg masses in in a beverage-sized for 5 hours. Conch should be (Fig. 5). thermos (0.26-gallon; 1-L). removed from the egg farm at the Researchers are looking for a reli- end of the breeding season to The crescent-shaped, sand-covered able way to induce egg laying in avoid overgrazing and poor egg egg mass can be found under the captivity. In 2000, scientists at the production the following season. anterior lip of the female conch (Figs. 3 and 5). Egg masses collect- Harbor Branch Oceanographic It is difficult to differentiate male ed directly from underneath the Institution were the first to and female conch from their females are hardier and easier to observe egg laying in captivity. appearance, although the females transport because embryo devel- One female and three male S. are usually larger. Size can be opment is minimal. It takes gigas conch were stocked (one used as a general indication of approximately 24 to 36 hours to conch per 100 square feet; one sex unless fishermen have altered lay an egg mass, and the eggs conch/10 m2) and held in a circu- this relationship by preferentially hatch in 3 to 5 days. It is not nec- lar breeding tank with an elevated harvesting the larger females. A essary to collect a full egg mass; sand substrate. The breeding tank more accurate, but time-consum- one-half or three-fourths of an egg was on a recirculating water sys- ing, method of differentiating mass will yield a substantial tem and was kept at 81 to 84 °F sexes is to place conch on their hatch. Or, small egg masses can (27 to 29 °C), 32 ppt salinity, pH sides with their lips pointing up. be combined for hatching. For 8.0, and ammonia 0.06 to 0.10 As they right themselves their transport to the hatchery, the egg mg/L (ppm). The breeding tank sex can be noted: a verge for a mass is placed in a plastic bag was inside a shaded greenhouse male and an egg groove for a filled with seawater inside a shad- and artificial lighting above the female (Fig 2). Another way of ed bucket of seawater. Conch egg tank was set on a 12-hour cycle determining sex is to observe masses can be shipped within 24 (8:00 a.m. to 8:00 p.m.). The conch in their mating position hours to other hatcheries or labo- broodstock were fed approximate-

Figure 5. Life cycle stages of the queen conch, S. gigas. (drawing by Bonnie Bower-Dennis). long (Fig. 5). The emerged veliger sis (Fig. 7d). The lobes are used is 300 µm SL and has two velar for locomotion, respiration and lobes (Fig. 7a), which divide into feeding. four by the fifth day (Fig. 7b) and Veligers are cultured in 130- to six by the eighth day (Fig. 7c). 530-gallon (500- to 2,000-L) coni- These lobes continue to elongate cal tanks with gentle aeration until the 0.04-inch (1-mm) SL (Fig. 8). To keep the veligers in veliger is ready for metamorpho-

a b

Figure 6. Egg mass incubating con- tainers and tank (a). Each egg mass container holds an individual egg mass (b) on a screen (c). The water upwells through the screen (d) and the water leaves via a small open- ing in the side of the container (e). (drawing by Jackie Aronson)

ly 50 to 70 g per day of prepared diet—a mixture of koi chow, Ulva seaweed, seawater and an algi- nate binder. Four egg masses were laid by the single female conch in captivity, and the c d hatched veligers were cultured ii successfully to the juvenile stage. Egg mass handling i iii In the hatchery the egg mass is disinfected to remove bacteria and predators such as worms, and crus- taceans. The egg mass can be dis- infected by dipping it in fresh iv water for 5 seconds or in a mild chlorine-seawater solution (0.5%) for 30 seconds, then rinsing it in three containers of seawater. The egg mass incubates for 3 to 5 days in an upwelling screen (75 µm) PVC container (6 inches in e diameter and 6 inches high; 15 Figure 7. Stages of queen conch, S. cm x 15 cm) with a flow rate of gigas, veliger development: 0.03 gallons per minute per egg (a) newly hatched, 2-lobed veliger mass (0.1 L/min/egg mass) (Fig. (300 µM); 6). On the day of hatching, the (b) four-lobed veliger (4 days old; developing embryos steadily 450 µM); rotate and the capsulated veligers (c) six-lobed veliger (8 to 10 days old; have velar lobes that are well- 600 µM); defined with cilia and red pig- ment on the foot. (d) metamorphically competent veliger (21 days old; 1.0 to 1.2 mm) Hatchery with labels for i) eye, ii) , iii) buccal mass, iv) on foot; If the feeding regime, tempera- and ture, stocking density and water (e) metamorphosed conch (1.2 mm). quality are optimal, the veliger (photographs a-d by Megan Davis cycle is approximately 21 days and e by Leroy Creswell) suspension, a PVC airlift (6 inches ing veligers, water exchanges all will die on day four. Stressed in diameter x 6 inches high; 15 start by using a 100-µm sieve and veligers will excrete mucus cm x 15 cm) with two air lines increase to a 350-µm sieve strands that trail behind the (without airstones) attached to toward the end of the larval swimming larvae and cause them either side is positioned 0.2 inches cycle. to clump together. This occurs (0.5 cm) from the bottom of the A hose is used to remove from overfeeding, high density, tank (Fig. 8). Conch veligers are the veligers from the tank (Fig. and rough water changes. The large and must be stocked at a rel- 8). This method is less stressful condition is usually temporary atively low density (560 to 760 to the veligers than draining and can be solved by decreasing per gallon; 150 to 200/L) com- them from the bottom of the food, lowering density, and pared to many bivalve species. tank. After the tank is drained improving water exchange meth- Density is gradually reduced dur- the veligers are gently hosed off ods. A momentary increase in ing the water changes to a final the sieve into the newly filled aeration will break the clumps of density of 95 to 150 veligers per tank. The tank is covered and, in veligers apart. gallon (25 to 40 veligers/L) at a flow-through system, the water Even though veligers hatch with . Optimal culturing is turned on. yolk reserves, they will begin temperature is 82 °F (28 °C) and A sample of veligers should be feeding on 6 to 36 ppt salinity. However, veligers 8 hours after hatching. Therefore, can be grown at temperatures of observed daily using a dissecting microscope (20X to 40X) to deter- to increase survival and vigor the 75 to 90 °F (24 to 32 °C) and veligers should be fed the morn- salinities of 26 to 40 ppt. mine their growth, development, and the amount of feed in the ing after hatching. Two species of Larval cultures are maintained gut. A healthy S. gigas veliger has phytoplankton or microalgae are either in a flow-through system cultured to feed conch veligers— (0.3 to 0.6 gallon per minute; 1 to • a dark gut that fills the top flagellated algae, Tahitian 2 L/min) or in static conditions. whorls of the shell (indication Isochrysis galbana or Caicos Higher densities can be main- of feeding); Isochrysis; and the diatom tained in a flow-through system. • clean velar lobes, fully extend- Chaetoceros gracilis or Chaetoceros Water changes begin the day after ed, and cilia moving in a muelleri. Batch cultures of phyto- hatching and occur every 48 wave-like pattern; are grown in carboys hours. Larvae cannot be dry- • increasing velar lobe and shell (5-gallon; 20-L) or cylindrical sun tubes (65-gallon; 250-L). The sieved; therefore, the PVC sieve whorl development; and (8 inches in diameter x 12 inches desirable cell concentration of high; 20 cm x 30 cm) used for • growth of 50 to 55 µm SL/day. Isochrysis in the larval tanks is 1.3 water exchanges is supported in a A veliger is diseased if it x 106 cells per gallon (5 x 103 cells/mL) for newly hatched bucket of seawater (Fig. 7). To • is slow to come out of the veligers and 6.6 x 106 cells per help cull the dead and slow-grow- shell, gallon (25 x 103 cells/mL) for • has bacteria and protozoa in metamorphically competent the shell or feeding on the veligers. Chaetoceros is added to veliger’s tissue, the culture starting on day 15 and • has lobes that are stunted or the final concentration in the show necrosis (Vibrio bacteria tank is 0.8 x 106 cells per gallon 3 infection), (3 x 10 cells/mL). In static larval cultures the phytoplankton is • moves erratically, added as a batch feed, whereas in • has debris or protozoa on the flow-through larval tanks the outside of the shell, algae cells are diluted with sea- • has a light gut (lack of food), water and drip-fed into the cul- and ture water for approximately 12 hours. • shows no growth and develop- ment. Metamorphosis If there has been a bacterial inva- Veligers are metamorphically sion (e.g., Vibrio) during the first competent about 21 days after Figure 8. Conical bottom larval 7 days, the veligers will show hatch. At this point their shell tank for culturing queen conch normal development but all of length is about 0.05 inches (1.2 veligers (a). An airlift is positioned them will die shortly thereafter. at the bottom of the tank (b). mm). The veligers are competent Veligers are siphoned from the tank If there is a toxicity problem when their eyes migrate outward, into a sieve suspended in a bucket (e.g., water quality, , new the are of equal length, of water (c). (drawing by Jackie PVC pipes and glue, insecticides), the pigments on the foot change Aronson) the veligers will not develop and from orange to dark green, the ctendium (i.e., gills) are elongat- searching for food with its pro- centration should be increased ed and functional, and the buccal boscis (Fig. 7e). If an extract slightly. During the metamorphic mass has developed (Fig. 7d ). dosage produces at least 60 per- process the veligers should be Several different substances can cent metamorphosis in the sam- placed in subdued light. After 4 to be used to induce metamorphosis ple, it should be effective on the 5 hours, the system is flushed in queen conch larvae, including large-scale. with water to eliminate the cue. potassium chloride, hydrogen In recent years, scientists have Newly metamorphosed conch can peroxide, epiphytic diatoms, and discovered a more cost-effective be kept in a recirculating system red macroalgae. Two of the most procedure for inducing metamor- or in a flow-through system. reliable inducers for large-scale phosis. Competent veligers are Water enters each shallow screen cultures are extracts from the red exposed to 50 µM of 3% pharma- tray through a small tube (0.15 to macroalgae Laurencia poitei and ceutical grade hydrogen peroxide 0.24 inches in diameter; 4 to 6 small doses of hydrogen perox- (0.06 mL of H2O2 /1 L of seawa- mm) (Fig. 9), creating a slight vor- ide. At a temperature of 82 to 86 ter) for 4 hours. The cost per tex in the downwelling tray. °F (28 to 30 °C), these cues batch of larvae is about $0.16, Conch are kept on the screen should induce 75 to 95 percent of compared to $15.00 with trays for 14 to 21 days until they the conch to metamorphose. Laurencia. Using hydrogen perox- reach an average size of 0.12 to The extract of L. poitei is pre- ide reduces the variability found 0.14 inches SL (3 to 4 mm SL). pared from old, thick, red-brown in natural inducers, and it is a The average growth rate is 0.180 stalks collected from shallow, simple, low-cost, safe method for mm SL per day or more. sandy, grass flats and transported commercial-scale induction of Before conch are fed, the trays to shore in mesh bags. The metamorphosis. are gently shaken to remove younger stalks, which are yellow- When a batch of larvae is ready wastes and to dislodge the conch orange, are slightly toxic to for metamorphosis, a shallow crawling on the sides. Newly veligers and will cause only a tray (8 feet long x 3 feet wide metamorphosed conch are fed small percentage of them to and as deep as 6 inches; 2.4 m x flocculated Chaetoceros gracilis for metamorphose. Onshore, the 0.9 m x 2.4 cm) is filled with sea- the first 2 to 3 weeks. For large- macroalgae fronds are rinsed and water and the inducing substance scale operations, this diatom can sorted to remove coral pieces, (Fig. 9). The solution is mixed be grown in 5,300-gallon (20,000- sponges and excess sand. Then a well, then eight shallow screen L) tanks located outside with no ratio of 2 g of Laurencia to 1 mL (250-µm) trays, each with an area cover. For smaller hatcheries, C. of seawater is blended for of 430 square inches (2,800 cm2), gracilis can be cultured in 5-gallon approximately 2 minutes in an are placed in the trough. The lar- (20-L) carboys or in 65-gallon industrial blender. The solution vae are stocked at 325 per square (250-L) cylinders. Chitosan, a is frozen for at least 2 days to foot (3,500 per m2). Veligers macromolecule from the exoskele- lyse the cells and release the should stop swimming 10 to 30 ton of , is used in the molecular cues. The frozen solu- minutes after they are exposed to flocculation procedure. Chitosan tion is thawed overnight, filtered the metamorphic cue. If they is purchased in a powered or through a 200-µm polyethylene continue to swim, the cue con- flaked form. screen, and the resulting extract refrozen. Four and one-half pounds (10 kg) of collected macroalgae produces 4.2 gallons (16 L) of blended slurry, which yields approximately 2 gallons (7.5 L) of extract. Before any new Laurencia extract is used, the proper dosage is determined by placing 25 compe- tent veligers in three different extract concentrations—7, 10 and 15 mL of Laurencia extract/L of seawater—for 4 hours. Then the veligers are removed from the extract and the percentage that has metamorphosed is deter- mined using a dissecting micro- scope (40X). A veliger has meta- morphosed when the velar lobes Figure 9. Metamorphosis tank (a) with incoming water (b) and screen trays are lost, it is crawling with its (c). (drawing by Jackie Aronson) propodium (foot), and it is The flocculating procedure begins nite (1 to 3 mm diameter) and ture for rearing juvenile conch is by adjusting the microalgae cul- constant water flow and air sup- 81 to 84 °F (27 to 29 °C). Growth ture to a pH of 6.0 to 7.0 with the ply. The water downwells rates range from 0.180 to 0.250 addition of muriatic acid (approxi- through the sand, is recirculated mm per day and survival rates mately 0.1 to 1.2 mL of muriatic through a sump and returned to are as high as 90 to 95 percent. acid/L of algae). The chitosan the trough. This system can also Conch are fed once a day with solution is well mixed into the be set up as a flow-through sys- either a gel-based diet or a com- algae culture at a dose of 5 mL tem. Depending on the size of mercial conch chow. The gel feed per L of algae. A stock solution of the conch, the sand trays are consists of ground koi or chitosan (10 g chitosan to 1% sprayed down every 2 to 4 weeks pellets (36 percent), dried Ulva acetic acid) is prepared in to remove accumulated waste sp. seaweed (16 percent), gelatin advance and can be stored for products. During this process, the or alginate (6 percent), and sea- several weeks. Sodium hydroxide sand and the animals are left water (42 percent). The gelatin or (5% or 5 g NaOH/100 mL fresh intact and the conch lie dormant. alginate allows the feed to water) is added to raise the pH to Juvenile conch (0.8 to 1.6 inches remain stable for approximately 8.5 to 9.0 (approximately 1.0 to SL; 2 to 4 cm SL) can be placed 48 hours. The diet can be manu- 1.5 mL/L of algae). The algal cells in shallow, circular, fiberglass or factured in a feed mill or made are stirred again for several min- cement ponds, or lined raceways, in smaller quantities using a utes until flocculation is at a stocking density of 14 conch stove and stainless steel cooking observed. The flocculated cells per square foot (150 conch/m2). pot. The approximate cost of the settle to the bottom of the vessel During this nursery stage, the processed diet is $3.20 per pound and can be separated from the density will need to be reduced with catfish pellets and $4.50 per “clear” water. If small quantities to seven conch per square foot pound when koi pellets are used. of flocculated algae are needed on (75 conch/m2). Adding sand to the The gel feed has a shelf life of 1 a daily basis, the settled algae can bottom will aid in shell formation week if refrigerated and several be stored in the refrigerator for and assist with biofiltration. months if frozen. up to 1 week. On the first day of Nursery systems also can be Juveniles 0.12 to 0.16 inches long metamorphosis, the conch are fed either recirculating or flow- 7 (3 to 4 mm SL) are fed approxi- about 6 x 10 cells per conch per through. Water should enter the day. Feeding increases to 20 x 107 mately 10 mg of feed per conch conch ponds or raceways from per day. Larger juveniles (1.2 to cells per conch per day for conch one or two spray bars to create a that are 14 to 21 days old. 1.6 inches SL; 30 to 40 mm SL) circular flow that exits through a are fed approximately 120 mg of central standpipe. The optimal Nursery feed per conch per day. Smaller flow rate is based on conch den- conch are fed about 15 percent of The post-larval conch (3 to 4 mm sity, temperature and feeding wet-meat weight. As they SL) are placed in sand troughs 10 strategy. To enhance growth and increase in size (2.4 inches SL; 6 feet long x 2 feet wide x 2 feet survival, the nursery ponds or cm SL) they are fed 2 to 7 per- high (3m x 0.6m x 0.6 m) at 316 raceways should be covered with cent of the wet-meat weight. The conch per square foot (3,400 100% shade cloth. Juvenile conch typical growth rate on the gel conch/m2) (Fig. 10). These troughs prefer shaded areas because in diet is 0.18 to 0.20 mm per day, have an elevated sand substrate the wild they are found buried in depending on temperature and made up of crushed coral arago- the sand. The optimum tempera- stocking density. Conch fed the commercial feed have a feed con- version ratio of 1.5:1 for dry weight of feed to total wet-weight of the conch (shell and meat). The leading edge of the shell of a healthy juvenile is thin and usu- ally covered with feed, sand and feces. The conch fills the shell, and the foot and operculum are easily seen in the aperture. An undernourished conch recedes into the shell, making it difficult to see the foot and operculum. Figure 10. Juvenile trough system with elevated support (a) for sand substrate When a conch is not growing the (b). The water in the tank (c) drains through the sand and into a sump (d); shell becomes covered with a the pump (e) sends the water into the tank and underneath the substrate (f). green or blue-green algae. (drawing by Jackie Aronson) Conch are most active at night. The stocking density for juvenile (University of Puerto Rico) have During the day they lie dormant conch should reflect the density contributed valuable data about with their apertures toward the found in the wild, which is one the feasibility of releasing conch sand substrate and tend to be par- to two conch per 10 square feet juveniles into the wild. (These tially buried when not feeding. (one to two/m2) or approximately studies released juveniles less When underfed, conch are active 4,050 conch per acre than 4 inches [10 cm] long.) First, during the day searching for food. (10,000/hectare). Cages can be release sites should provide the Juvenile conch in poor health are stocked at a higher density (one same conditions as grow-out often observed on the sand sur- conch per square foot; 10/m2) environments. Released animals face, positioned with their opercu- than open sea pasture; however, should be more than 3 inches la upward and their bodies par- the natural food supply may long (> 7.5 cm SL) and equiva- tially extending out of their shells. need to be supplemented with a lent to wild stocks (e.g, shell In this state, their response to a prepared diet. morphology, shell strength, burial stimulus is often sluggish. This Stock must be rotated through patterns, predator avoidance). behavior could be a result of stag- the sea pasture to avoid overgraz- Released conch should be nant water flow (e.g., low oxy- ing. The best grow-out sites are hatched from several egg masses gen), overfeeding, or stress from historical nursery grounds. These to improve genetic diversity. handling. Remedies include flush- sites have a sandy bottom with Planting should be done in the ing the tank, feeding less, and/or an intermediate density of sea- fall and before the full moon to adjusting the water flow rate. The grass (56 to 84 Thalassia shoots lessen , and several kicking behavior conch some- per square foot; 600 to 900/m2) thousand conch should be times exhibit is usually a sign of and high algal productivity. They released at one site. Harbor stress and has been observed are 7 to 13 feet (2 to 4 m) deep Branch Oceanographic Institution when the animals are in low-oxy- and have strong tidal currents (1 is researching ways to improve gen situations or are fed certain to 2 knots) to flush the area and husbandry techniques so that types of artificial feed (e.g., bring in new feed. juvenile conch from aquaculture Spirulina). facilities will be similar to their Grow-out from 2.8 to 7 inches SL wild counterparts. It was deter- Grow-out (7 to 18 cm SL) will take approxi- mined that conch grown at a mately 1.5 to 2 years at a growth Larger juveniles can be grown high density of 18 to 37 conch rate of 0.15 to 0.20 mm per day. per square foot (200 to 400/m2) to from 2.8 to 7 inches SL (7 to 18 Conch are harvested from the cm SL) in a sea pasture with a 3 inches SL (7.5 cm SL) on arago- sea pasture by divers working nite sand had the strongest shells predator-exclusion fence or in from small boats. They can be cages. Suspected or known preda- and were able to burrow into the processed on-site or sold live to sand. tors of queen conch include restaurants or wholesalers. brachyuran , hermit crabs, Survival in the sea pasture The success of a conch release spiny lobster, , fish, should be 60 to 90 percent, program will depend on the cost , rays, turtles and other car- depending on the effectiveness of of seed, the quality of the seed nivorous gastropods. The fence the cages or fences, the availabil- stock, and the participation of the should extend from the bottom to ity of feed, and the success of government and the local fisher- the high-tide line. A variety of the predator trapping program. men. Given the high cost of fencing or cage material can be conch seed (from $0.20 each for used to exclude predators and Stock enhancement 2-cm seed to $0.75 for 7- to 9-cm contain conch. Large, circular seed) stock enhancement may cages (80 feet in diameter, 5,400 Reintroducing conch in over- not yet be economically feasible. square feet; 25 m in diameter, fished habitats has been suggest- However, every conch that sur- 500 m2) with mesh openings (6 to ed as a way of re-establishing vives to adulthood can be mea- 8 inches in diameter; 15 to 20 cm conch spawning where the natur- sured in terms of its reproductive in diameter) will help to exclude al population is not likely to output rather than as a product large predators; smaller mesh (2 recover. To date there have been for the fisheries. Therefore, inches in diameter; 5 cm in diam- no large-scale reseeding efforts releasing juvenile conch and eter) placed along the bottom will with queen conch juveniles. transplanting adult conch to form exclude smaller predators and However, several stock enhance- spawning aggregations may be help to keep juvenile conch from ment studies conducted in the ideal way to bring back escaping. Inexpensive traps such Florida (Florida Fish and Wildlife depleted populations. Grow-out as empty adult conch shells can Conservation Commission), the in pastures and pens is the sug- be used to catch octopus; baited Bahamas (University of Miami, gested method of producing traps can collect and gas- Caribbean Marine Research conch for the fisheries market. tropod ( tulipa and Center) and Puerto Rico ponum) predators. Markets s e a water systems. Conch are mated that another 3,000 or so shipped dry. On the day of ship- conch per month could be sold to Queen conch has long been a ment, the conch are placed on top the wholesale aquarium market at f avorite item on the menus of of layers of moist paper towe l s $0.75 each, for an additional ye a r l y restaurants in the Caribbean and inside plastic bags that are packa g e d gross revenue of $27,000. The main Florida. The tasty, tender meat is inside insulated boxe s. A small a d v antages of selling smaller conch -rich (20 percent) and con- amount of oxygen is added to the are that the product is ready for tains no saturated fat. Conch meat plastic bags before they are closed. m a r ket in 6 to 12 months and there has a crunchy texture similar to Cold packs keep the conch cool dur- is no need for the sea pasture. that of and a ing shipment (72 °F; 22 °C). Conch Another market for conch is other with the sweetness of . are shipped by air and will arrive Because the market is based almost nursery and grow-out farms. The with 100 percent survival if ship- estimated value of conch seed is entirely on wild-harvested animals, ment time is less than 36 hours. the demand is for legal size conch $0.01 per mm of shell length, or (3 to 4 years old) with fully formed Some restaurants prefer to buy $0.10 for 0.4-inch SL (1-cm SL) small conch shucked or remove d conch and $0.70 for 3-inch SL (7- l i p s. Retail prices for wild-harve s t- ed conch from , the Tu r k s from the shell. A specialized shuck- cm SL) conch. There is an ever- and Caicos Islands, Belize and the ing tool is used to release the conch increasing need for countries to Bahamas range from $6.00 to muscle from the columella. The have centralized hatcheries that $15.00 per pound. guts are removed and the conch are can supply nursery and grow-out p a c kaged in 1-pound bags for ship- farms with seed conch. N ew markets have been estab- ment. There are approximately 96 If a farmer planned to harvest lished for smaller cultured conch, conch per pound at 2.4 inches (6 n ow that large numbers of farmed- 500,000 legal-size conch per year cm) SL and 43 conch per pound at 4 from sea pasture cages, the farmer raised conch are available on a reg- inches (10 cm) SL. Bags of conch ular basis from the commercial would have to stock 50 acres (20 are refrigerated or frozen and pack- hectares) of sea pasture at 1 conch conch farm in the Turks and aged in coolers for shipment. 2 Caicos Islands. CITES has per square foot (10 conch/m ) and a p p r oved these farm-raised conch Farm-raised conch have been well allow for rotation. Because to be sold live in-the-shell or received by chefs and their clients. the grow-out time is 1.5 to 2 years, s h u c ked at a sub-legal size (1.2 to 4 Several chefs have stated that the farmer should have two crops inches SL; 3 to 10 cm SL). It is farm-raised conch is sweeter and in the sea pasture at the same more tender than wild conch. The time. Therefore, a total of 100 very difficult to locate large num- bers of conch smaller than 4 inch- tenderness appears to be related to acres (40 hectares) are needed. If es SL (< 10 cm SL) in the wild, so their small size and the fact that optimal survival is 90 percent, there is little concern about they are sold live or fresh, where- 557,000 juvenile conch would have exploiting this size juvenile from as most wild conch are larger and to be planted in the sea cages to natural habitats. These hatchery- sold frozen. yield the 500,000 legal-size conch. These farmed-raised conch will reared conch are sold live to Economics restaurants in Prov i d e n c i a l e s, the produce 100,000 pounds (45,350 kg) of meat at five conch per Turks and Caicos Islands, Florida Now that queen conch are being pound or 0.18 pounds of meat per and New York at a wholesale price cultured successfully and wild conch (85 g of meat per conch). of $0.50 to $0.75 each. These small stocks have dwindled below sus- The farmer should expect to get a conch are served in traditional tainable levels in several countries, premium price for farm-raised dishes, , pael- private and government groups conch based on niche-market las and ; they also can be from Caribbean countries have prices established by the Caicos s e r ved -style or as tempura, expressed interest in setting up Conch Farm (up to $20.00 per and are boiled or steamed to be hatcheries for seed production, pound wholesale). At this price the s e r ved as medallions. stock enhancement and commer- annual gross revenue would be cial grow-out. The second market for small approximately $2,000,000 per year. conch is the aquarium trade, To be economically successful, a The infrastructure required to pro- where the wholesale price to commercial queen conch farm duce 500,000 conch per year retailers is $1.75 to $2.25 each. needs to produce at least 500,000 includes an egg farm, a hatchery, a Conch sold for aquaria are 1.2 j u venile conch per year either to post-larval and nursery facility, inches (3 cm) SL and graze on supply the specialty markets for and a grow-out pasture (Table 1). If algae and diatoms from the sand, small conch or to stock into grow - conch will be processed on site, a rocks and glass of the aquaria. out pastures. If the farm sells processing facility is also required. 500,000 small conch (2.4 to 4 inch- Before live conch are shipped, they It is estimated that 12 staff mem- es SL; 6 to 10 cm SL) to the food are sorted by product type (e. g . , bers would be needed to operate m a r ke t s, the gross yearly reve n u e food or aquarium market) and the onshore and offshore facilities would be about $375,000 ($0.75 purged for 12 to 24 hours (no feed) of a farm this size. in flow-through or recirculating each for 4-inch SL conch). It is esti-

Summary sustainable, a commercial conch Delgado, G. A., C. T. Bartels, R.A. farm should produce 500,000 juve- Glazer, N. J. Brown-Peterson The queen conch, S. gigas, is a nile conch per year. and K. J. McCarthy. 2004. prized delicacy throughout the Translocation as a strategy to Caribbean and Florida and has Acknowledgements rehabilitate the queen conch long been harvested both for its (Strombus gigas) population in Special thanks to Amber Shawl, meat and its beautiful shell. the Florida Keys. Fisheries Ashley Spring, Peter Van Wyk and has depleted Bulletin 120:278-288. wild populations. Culturing queen Nancy Daves, who contributed conch could relieve fishing pres- information for this publication. Randall, J. E. 1964. Contributions sure and provide animals for This is Harbor Branch to the of the “queen restocking overfished habitats. Oceanographic Institution, Inc. conch” Strombus gigas. Bulletin Methods of culturing juvenile contribution # 1605. of Marine Science of the Gulf queen conch are well established. and Caribbean 14:246-295. Egg masses are collected from the Suggested readings Shawl, A. and M. Davis. 2004. wild and the hatched veligers are Davis, M. 2000. Queen conch Captive breeding behavior of cultured for 21 days on phyto- (Strombus gigas) culture tech- four conch. plankton. After metamorphosis, niques for research, stock Journal of Research the post-larval conch are grown on enhancement and growout 23:157-164. sand in shallow tanks until they markets. Pages 127-159 in M. Stoner, A. W. 1994. Significance of are almost 1 inch (2 cm) SL. They Fingermna and R. habitat and stock pre-testing are fed a combination of flocculat- Nagabhushanam, editors. for enhancement of natural ed phytoplankton and prepared Marine Biotechnology. Science fisheries: experimental analy- feed. Conch are kept in nursery Publishers, Inc., USA. ses with queen conch. Journal ponds onshore until they are 2.8 Davis, M., B. A. Mitchell and J. L. of the World Aquaculture inches (7 cm) SL. Then they are Society 25:402-424. placed in a sea pasture for grow- Brown. 1984. Breeding behav- out. Small juvenile conch are mar- ior of the queen conch keted as specialty food. Legal-size Strombus gigas Linne held in a conch are used in more traditional natural enclosed habitat. dishes such as conch fritters, salad Journal of Shellfish Research or chowder. To be economically 4:17-21.

SRAC fact sheets are reviewed annually by the Publications, Videos and Computer Software Steering Committee. Fact sheets are revised as new knowledge becomes available. Fact sheets that have not been revised are considered to reflect the current state of knowledge.

The work reported in this publication was supported in part by the Southern Regional Aquaculture Center through Grant No. 2003-38500-12997 from the United States Department of Agriculture, Cooperative State Research, Education, and Extension Service.