Oyster Culture in North America

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Oyster Culture in North America
By Leonard Lovshin Department of Fisheries and
Allied Aquacultures Auburn University, AL 36849
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Distribution
The eastern oyster, Crassostrea virginica, is
native to the East coast of Canada and United
States, Gulf of Mexico and Caribbean, and as far
south as the Northern coast of South America.
pacific oyster
eastern oyster
The pacific oyster, Crassostrea gigas, was
introduced from Japan and extends from Alaska to
Baja California
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Oyster Biology
Feeding Habits feed on anything 3-12 microns in
size by filtering from the water and receive
nutritional value from phytoplankton and
detritus Water temperature 25 to 30oC for best
growth
Salinity 10 to 22 ppt for best growth
Growth to 15 cm 9 to 12 months in the Gulf of
Mexico
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Life History
1. Reach sexual maturity at 1 year of age.
2. Protandric - Young oysters are usually male
and change to female after first spawning season.
3. Water temperatures above 25oC trigger spawning
in the Gulf of Mexico. 4. Salinity above 10
ppt. 5. Spawn between March and November
Larval period is 14 to 21 days
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Spawning Fertilization
Sperm triggers females to release eggs. Females
can release millions of eggs.
Larvae with a muscular foot looking for a site to
set.
sperm
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Wild-Caught
1. Seed Production - wild
Seed can be collected from the wild on shells and
artificial substrates (cultch) placed near
spawning grounds.
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Hatchery-Reared
2. Seed Production - hatchery
Adults are induced to spawn and the larvae are
fed algae until they are ready to set.
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Triploid Oysters
Triploid oysters that can not reproduce are
produced in a hatchery. Triploid oysters grow
faster than normal diploid oysters and have good
flavor (high glycogen content) during the summer
spawning season.
gonad
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Eyed Larvae
Larvae ready to set can be placed in upwellers
containing crushed shell or tanks with bags of
shell
tanks
larvae
upwellers
crushed shell
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Cultchless Spat on Shell
Spat on crushed shell are single set and spat on
whole shells are multiple or cultch set.
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Nursery
Spat can be placed in protected intertidal zones
to grow and harden for several months.
Exposing the oysters to the air protects them
from predators.
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Growout of Spat on Whole Shell
Spat on whole shell are grown 1. On the
bottom in reefs 2. On ropes suspended off
the bottom
Shells with spat are moved from spawning or
nursery grounds to growout areas. Little care is
given to the oysters. Culture is extensive.
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Cultchless Growout
2. Cultchless or single oysters are grown in
bags
trays
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Cultchless Growout
Trays and bags are suspended off the bottom by
ropes tied to rafts and floats or on stationary
platforms. Culture is extensive.
raft
platform
floats
Oyster density and sizes, predators and fouling
are controlled.
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Grading
Shaker table grader
Oysters are graded several times to assure
uniform growth and size at harvest.
Uniform sizes
Variable sizes
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Control of Predators
Predators are controlled by exposing the oysters
to air, keeping the oyster off the bottom and
manual cleaning.
starfish
black drum
crabs
oyster drill
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Control of Fouling
cleaned
fouled
Removed by drying, pressure spraying, manual
cleaning and dipping in a toxic solution.
Fouling organisms compete for space and food with
oysters and restrict water flow through
enclosures
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Harvest of Reef Oysters
Reef oysters are harvested from the bottom with
tongs and dredges. Oysters are ready for harvest
in 1 to 5 years depending on water temperatures.
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Harvest of Farmed Oysters
Oysters cultured in bags, trays and on ropes are
harvested mechanically because of their weight.
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Purging
Oysters are often contaminated by bacteria and
viruses harmful to the consumer of raw oysters.
Oysters can be purged by moving them to clean
water in the ocean or on land.
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Market
Oysters are sold live, fresh and frozen on the
half shell and shucked, canned and smoked.
Fresh on half shell
Frozen on half shell
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World Yield of Oysters
about 3,944,000 mt in 2000
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1999 U.S. Oyster Yields
Wild and farmed harvest of oyster meat was 12,587
mt.
Harvest of eastern oyster meat was 9,109 mt or
72 of the total harvest. Harvest of pacific
oyster meat was 3,478 mt or 28 of the total
harvest.
Meat is 10 of the whole oyster weight
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The End