The New Rules for Safely Eating Seasonal Seafood (2024)

An old rule of thumb warns that shellfish should be avoided during months with no R’s—May, June, July, and August—exactly the season that many of us are heading for the shore and eager to sample the fruits of the sea.

Do you really need to take the entire summer off from shellfish? And is the old saw about avoiding sushi on Mondays still accurate? We decided to check in on some of the old and new guidelines for seafood-eating to see what’s out of date, what new rules have fallen into place, and how to gorge ourselves on aquatic delights without running the risk of food poisoning (or worse).

Season-to-Season Guidelines

The old “months with no ‘R’s” rule comes from a couple of places, says Kate Brogan, of National Oceanic and Atmospheric Administration’s Fisheries Department. First, oysters spawn during summer, and during this process their glycogen (stored starch that imparts a sweets taste) turns into gametes, changing the flavor and texture so that they are, as Brogan puts it “well, not great.” Second, says Brogan, “In the pre-refrigeration days you did not want to eat an oyster that had been sitting in the hot sun all day.”

These days, says Brogan, “there really are no months without an R because we have Refrigeration now!” And newer regulations also mean that the R-rule can be safely set aside. Some states have oyster curfews to ensure that growers must harvest their oysters before noon or midmorning, depending on the month, “to avoid the shellfish being out in the midday heat,” she says. So while oysters may not be taste the best during hot summer months, they shouldn’t make you sick (and the same goes for other shellfish).

Another possible source of the R-month rule, however, is that harmful algal blooms are more common in warmer months, according to the EPA, which also warns that climate change is making these blooms more common year round. Some species of phytoplankton produce toxins, which in turn can enter the food chain when shellfish or other sea creatures eat that phytoplankton, leading to foodborne illness. These can have serious effects, ranging from digestive distress to numbness, tingling, even mild memory disturbances, says Dr. Lynn Grattan, of the University of Maryland School of Medicine,who studies the effects of marine toxins on coastal communities.

This is a good reason to use caution when eating shellfish, but this doesn’t necessarily mean avoiding shellfish during summer months, says Grattan. “While there are some regional patterns for the emergence of harmful algal blooms, in the US, some fish or shellfish can retain the toxin for long periods of time. Thus, the bloom may be over, but the fish or shellfish may still be toxic.”

The best bet is to opt for US-based fish and shellfish, says Grattan. “In the US there are strict regulator guidelines for fishing, harvesting and distribution which are carefully and expertly monitored,” including monitoring of harmful algal blooms. Grattan advises consumers to watch out for, and follow, any warnings or closures from state Departments of Health or Fish and Wildlife, and to pay close attention to any advisories offered on restaurant menus. Harmful algal blooms have been reported in every coastal state, as well as the Great Lakes. Many states issue local warnings, and NOAA maintains a website with early warnings for harmful algal blooms around the country where you can alsosubscribe for updates on blooms in certain bodies of water. These warning systems aren’t perfect, and Grattan notes that “seafood consumption is the leading cause of foodborne illness with known etiology.” But you can lower your risk by eating domestic seafood and making yourself aware of any warnings—no matter what time of year.

Week-to-Week Guidelines

In his 2000 memoir Kitchen Confidential, Anthony Bourdain said he never orders fish on a Monday. In New York City, he wrote, the fish markets were closed over the weekend and restaurants did not get fresh fish delivered on Sundays, so on Monday the fish was likely to have been sitting around for a couple of days. This rule has definitely made the rounds, with plenty of online message boards debating whether sushi and other restaurant seafood is off limits on Sundays, Mondays or both.

But last year, Bourdain himself declared this rule outdated, because the demand for and knowledge about seafood is so much greater than it was even 15 years ago, and restaurants have adjusted their schedules and supplies accordingly. “It was a different world. Now, we know what good fish should look like and smell like,” he told Business Insider in 2016, “and the market has had to respond to that.” So as long as it’s a reputable restaurant, any day of the week is fair game.

Minding That Mercury

No matter what time of year or day of the week you’re eating seafood, one rule still holds true: don’t overdo it, lest you put yourself at risk of mercury poisoning. The heavy metal accumulates most in large, predatory fish such as swordfish, tuna, and sharks, but other species like bluegill and striped bass can contain enough mercury to cause problems for people who eat fish regularly. Those who are pregnant or nursing should avoid these species altogether (you can see the full FDA guidelines here). Dr. Michael Gochfeld, MD/PhD, who specializes in mercury poisoning, says that some people who eat fish several times a week will show signs of mercury poisoning. “A recurring theme in our clinic is, ‘for health reasons, I ate a can of tuna every day for years.’”

Gochfeld strongly believes that fish is part of a healthful diet, up to one once or twice a week. People who eat fish more often than that, he advises, should pay close attention to to the mercury levels in their fish, and aim to eat fish that are very low in mercury, and stick with 3-4 ounces per meal. Smaller species, like anchovies, sardines, and scallops, are particularly low in mercury; catfish, salmon, and tilapia are also safe bets. For more details, there are lots of guides out there, including this one from the NRDC.