Oysters 101

Related stories … Gulf Coast Oyster Outlook for TX, LA, FL

(See video at bottom of story – how to shuck an oyster.)

Evidently, the only appropriate answer to the question, “Who should I speak to about Gulf Coast oysters?” is “Dr. Sammy Ray.” That’s the only answer we got each time we asked. Although Dr. Ray officially retired from Texas A&M – Galveston in 1990, he is still active, even at age 92, in oyster research and university affairs. He describes himself as “an oyster doctor who makes house calls.” Dr. Ray has won a boatload of academic awards, and it seems he’s held just about every position, including interim President, at A&M-Galveston. His research on oyster diseases is legendary in the scientific community.

When told that several other scientist referred to him as “the” expert on oysters, he laughs and says, “I’ve worked on oysters for over 64 years. If I didn’t learn anything over that time, maybe something just sunk in.” Speaking to the affable Dr. Ray was a delight. He gave us a crash course on Oysters 101, which we hope you’ll find as enlightening as we did. That said, here we go!

The Eastern Oyster, the only commercial species in the Gulf, starts out in the nearshore waters during spawning, which occurs from late spring to early fall. Some oysters spawn all at once, others throughout the summer. They start out as embryos, then progress within a day or so to a larval stage that lasts 14-16 days. As larva, they have a weak swimming ability and start to grow a shell very quickly.

Once the larva mature, they must find something hard to stick to, a process called “setting”. If they don’t find something hard to stick to, they settle on the soft bottom and suffocate. The freshly set oyster is called a “spat”, a term that applies to young oysters under 1” in length.

When set, an oyster becomes sexually mature in only 6-8 weeks. Seventy five to eighty percent of young oysters are male, but as they grow older, they begin converting to female. A female can release 50-75 million eggs per season.

Oysters are filter feeders. They suck in plankton, algae and pretty much anything else in the water, remove what they can eat, then spit out the remainder. This filtering is important in cleaning bays, since an adult oyster can filter 48 gallons of water in 24 hours. Oysters are our organic water filters.

The amount of salt in the water that the oysters filter is a key to their survival (along with water temperature). Oyster need salinity, but not the full salinity of the Gulf, which offshore averages 35 parts per thousand (ppt), or 3.5% by volume. In the bays where Gulf oysters grow, salinity is usually less than 35 ppt due to rain and river run-off. Drought conditions increase salinity, and flooding decreases it. They can survive in water from 5 ppt to 35 ppt, but the sweet spot for oysters is salinity between 15 and 20 ppt. Oysters actually thrive and taste better in higher salinity, but their enemies thrive in higher salinity even better. The two main enemies of Gulf oysters are the southern oyster drill and a parasite known as dermo. Oyster drills are snails that bore into an oyster’s shell and kill it. Dermo infects oysters and kills them. In salinity above 15 ppt, these two enemies increase dramatically and can destroy an oyster population. The higher the salinity, the worse the enemies become.

Assuming it isn’t killed by its enemies, an oyster will continue growing, and in 18 to 24 months, it reaches 3 inches in length, which is the legal minimum size for harvesting. Remember the old adage about not eating oysters in months without an “R”? There are reasons for that saying, but it isn’t a rule, more like a guideline. Oysters spawn in the warm summer months. When they spawn, they lose glycogen, a substance that makes them tastier. They also lose a lot of weight. It takes twice as many pounds of summer oysters to make one pound of cooked oysters. Overall, summer oysters will be smaller and less tasty than cool weather oysters.

From a safety standpoint, there is a bacteria known as V. vulnificus that occurs naturally in warm salt water, which can be transmitted to humans by eating raw seafood, including oysters. V. vulnificus usually only affects persons with health problems, like impaired immune systems or liver disease. People with those health problems should avoid eating raw seafood, including oysters, because the bacterial attack in such persons could be fatal. Cooking kills the bacteria, so cooked seafood and oysters are fine.

If you buy oysters to consume at home, do not store them in water in an ice chest. When they are taken out of their native salt water, oysters close their shells tightly, which preserves their inner moisture and juices. If you submerge them, they open up and start to lose their natural moisture. They will keep in a dry sack at room temperature for two to three weeks, although the fresher they are, the better they taste.

Congratulations, you’ve completed Oysters 101. Dr. Ray made our lesson fun and easy to understand. We hope you enjoyed the course. Now you can use your new knowledge to dazzle your friends and family!

Related stories … Gulf Coast Oyster Outlook for TX, LA, FL

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