While I, personally, think shellfish taste kind of like something you might find in the back of your throat when you have a bad cold, some people love them. But why do they make you so sick? And why are you told not to eat shellfish during the summer? It’s not just important to think about what you eat, but what about what you eat eats, too.
Shellfish eat plankton, mainly a little guy called a dinoflagellate. (And no, “dinoflagellate” does not mean “dinosaur fart” in Latin.) Dinoflagellates excrete tiny amounts of toxins, which can cause a lot of problems for the sea life around them, but don’t really effect us. . .except if we eat a shellfish that has enjoyed one too many plankton. The toxins build up in the shellfish’s gut, and then we eat a whole lot of them at once. There are four different types of shellfish poisoning (I’ll spare you the details) but they can affect everything from your stomach to your memory.
So why the “months that have an R” myth? Supposedly, you’re only supposed to enjoy shellfish from September through April. AKA, not in the summer. This is because the plankton blooms are seasonal, meaning there are more phytoplankton in the summer, just like there are more flowers and trees. More dinoflagellates for the shellfish to eat equals a higher likelihood that you might get sick.
Luckily, most commercially harvested shellfish is very carefully monitored, so it is unlikely to make you ill. If you go out oyster harvesting by yourself, though, you might want to be careful. A delicious dinner date could easily turn sour, and nothing screams “beach party” quite like all of your guests becoming excruciatingly ill.