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AC111 Culturing Oysters, Clams, Crayfish and Shrimp

Aquaculture Library

MAIN IDEA:

• How are oysters, clams, crayfish and shrimp cultured?

Oyster culture

• 100 years old in United States• 2 most common types:

• Cupped (Crassosterea)• Flat (Ostrea)

• Water must be free of toxic substances associated with industrial and domestic pollution.

• Protected bays, estuaries and controlled environments

Oyster seedstock

• Oysters are protandrous – they change sex

• Gradually warming water temperatures trigger production of eggs and sperm (gametes)

• Larvae development• External for cupped oysters• Internal for flat oysters

Oyster development

• Oyster larvae – somewhat mobile• Veliger larvae – complete digestive systems,

voracious appetites• Eyed larvae – resemble adults, attach to clutch• Spat – oysters attached permanently. Dime-

sized with shell within 3 months.• Sexual maturity in 1 year. Most growth in first 3

years.

Oyster culture method:

• Larvae come from the wild or hatcheries.• Oysters are grown on stakes, umbrellas, racks,

rafts, long lines or suspended in trays and nets.• Oysters are filter feeders, eating algae.• Problems include disease, parasites, salinity,

temperature, stress.• Predators: oyster drills, starfish, flatworms,

crabs, fish

Making money from oysters …

• ¼ acre could yield 2.9 tons of meat/year

• Harvesting can be primitive or modern

• Sold in the shell,shucked or cooked.

NOAA photo by Bob Williams

Clam culture:

• Clam harvesting relatively simple and inexpensive

• Many part-time and recreational clammers

• Cultured because of shortages and strong demand

Clam seedstock and breeding:

• Spawning triggered by temperature• Protrandrous – may change sex• Stages:

• Veliger larvae drift or swim for 7-14 days and eat algae.

• Pedivelger burrow into sand or mud.

• Commercial hatcheries are intensive and land-based close to a coastal river or estuary.

The clam’s environment:

• Needs clean seawater• Vulnerable to changes in salinity• Grow where they can burrow – soft sand, mud,

rubble• Best growth with coarse substrate and silt clay• Filter feeders• Problems with poor water quality, bacteria,

fungi, toxins, parasites

Making money from clams:

• Harvesting uses rakes, hoes,patent tongs, modified oysterdredges, modified surfclam dredges and hydraulicdredges attached to conveyors.

• Most sold in the shell bybushel or counted

• Smaller sizes more valuable• Eaten raw or cooked

NOAA photo by Dr. Roger Mann

Culturing crayfish in ponds:

• Ponds simulate natural water cycle

• Population is self-sustaining

• Found in temperate fresh water throughout the world

• Natural habitat includes swamps and marshes

• They eat decaying plant material.

Crayfish pond water levels:

• Ponds drained in late spring/early summer

• Crayfish burrow and reproduce.

• Grasses and semiaquatic plants provide food and cover.

• Water quality is key to good production

Feeding crayfish:

• Decaying vegetation

• Commercial fish feed not economical

• Agricultural forages and byproducts

• Lime may benefit plants and reduce disease.

Making money from crayfish:

• Proper oxygen and temperature

• Intensive harvesting throughout season

• Traps checked daily

• Sold whole, cooked,frozen and inprepared dishes

USFWS photo by Eric Engbretsen

Culturing prawns and shrimp:

• Most widely cultured saltwater species

• Increasing demand

• Also freshwater culture in United States

Shrimp/prawn seedstock:

• Breed readily in captivity• Larval shrimp or• Eyestalk ablation induces spawning• Young larvae are fed brine shrimp• Older shrimp eat plankton, fish, soybean

cake, peanut cake, rice bran or most commonly a commercial, artificial, complete diet.

Shrimp/prawn concerns:

• Vulnerable to viruses, bacteria, fungi, protozoa, flukes, tapeworms, nematodes.

• Microsporidians cause “milk” shrimp

• High-density, confined shrimp lead to disease.

Making money from shrimp/prawns:

• Harvest with seines, dip nets or by draining the pond

• Growth varies with pond management

• 100 days or moreto harvest

• Sold fresh (on ice),frozen or processed.

Photo by Rick Parker is UBP.

This presentation was produced and is copyrighted by Stewart- Peterson®, Inc. 2004-2005. Permission is granted for use by active AgEdNet.com® subscribers. All other use is prohibited.

STEWART-PETERSON and AGEDNET.COM are registered trademarks of Stewart-Peterson, Inc.

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