The first and most compelling argument is that Red Tide most often occurs during summer months. This refers to high concentrations of an algae that is toxic to humans. If we eat shellfish that have absorbed this toxin, we can get pretty darn sick. The condition is known as "paralytic shellfish poisoning," or PSP.
However, red tide levels are closely monitored these days and harvesting is banned during those times. Shellfish are also regularly inspected and tested for toxin levels. It's not very likely that any shellfish reaching the market would contain harmful levels of the toxin. Many shellfish, especially oysters and mussels, are also now farmed instead of harvested from the wild, further decreasing the chance of contamination.
The other argument for the "R" rule is that shellfish usually spawn during the summer months. A rest is needed to let the shellfish repopulate. Spawning shellfish also taste different than at other times of the year, and they have a flavor and texture that many people find off-putting.
In our opinion, it's best to talk to your fishmonger or restaurant server whenever buying shellfish that you plan on eating raw. They can tell you whether the shellfish were farmed or from the wild, whether they're spawning, and answer concerns about food safety.
Do you eat shellfish during the summer?
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