Oysters - Yummy in my Tummy!

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Oysters

Of all the oysters produced 4,400,000 mt (98%) are a single species – the Japanese oyster (crassostrea gigas)

WHY?

1.     Fast growth

2.     Highly adaptable

3.     Demand -> taste/size

A little bit of “Oyster history”

-       Olympia oysters is the native spcies

-       S.F. oyster beds depleted by 1851 as a result of overharvesting

-       After that east coast oysters arrived by ship in barrels and cost 6$ a piece

With the opening of the transcontinental Railroad in 1875 “relaying” of Eastern oyster seed for growout in S.F> bay was started

-       1889 1.5 mt of seed imported

-       1899 1,100 mt of oyster meat produced

-       1908 down to ~ 600 mt of oyster meat

-       1919 Eastern oyster stocks suffered a massive mortaility

-       1921 Seed shipments discontinued

-       1939 Holding of imported stock halted

Japanese or Pacific oysters

-       Tougher and more suitable for aquaculture than the Eastern Oyster

-       Grows in brackish water upwards of > 16 ppt salinity

-       Grows at temperatures between 10-30 C

-       Withstand <0C

-       Withstands period of turbid water conditions

Problem – requires temperature greater than 20C for spawning

Oyster Life cycle

Fertilized Egg > Trochophora Larvae > Veliger larva > Spat (few mm size) (all done in hatercy up to this point) > Adult stage

Cultch

-Cultch is used in shellfish aquaculture as a substrate on which oyster spat can grow.

- The clean shell (cultch) is used in the hatchery to receive larval settlement

- Oyster seed is shipped to grow-out areas a spat on cultch

- After 1-4 years the settled oysters are removed and the empty shells recycled as cultch

Development of Oyster Hatcheries on the U.S. West Coast – 1980’s

Drivers

1.     Cost of Japanese spat was rising

2.     Infrequent natural spawning of C. gigas because of low water temperature

Broodstock used in oyster hatcheries

-Broodstock is conditioned for 2-6 weeks in flow-through trays while being fed algae

- generally, 30% males (1.5 – 2 years old) and 70% females (2.5 years and older) are used as broodstock

- Each female will produce millions (60-90 million) eggs

Induction of oyster spawning

-       Temperature shock

-       Spawning = excretion of gametes (unfertilized eggs and sperm) into the water

-       Blender technique to maximize fertilization

Oyster Harvest

Oyster cultured in bags, trays and on ropes are often harvested mechanically because of their heavy weight

Grow-out in California takes 13-18 month to produce a 4-inch oyster.

Shellfish Food safety regulation

National Shellfish Sanitation Program (NSSP) under supervision of the FDA

-Requires that both farmed and wild harvest-growing areas be distinctly demarcated

- Requires that each growing area is regularly tested for pathogens and classified as to water quality as determined by fecal coliform (gut bacteria0 counts

Food Safety Problems

1.     Deadly bacteria – can infest oysters and causes lethal septicemia in individual with impaired immune system

2.     Toxic algae (Cooking does not destroy these algal toxins)