The fish you should be eating...

...but probably aren't.

Although up to 500 different species of fish and shellfish are consumed in the United States, The Big Three—shrimp, canned tuna and salmon—accounts for more than half of the seafood Americans eat. Our myopic tastes hurt ecosystems and rob us of different nutrition profiles.

“Tuna and salmon became staples in the American diet because they were readily available, great sources of omega-3s and protein, and easy to prepare,” says TJ Tate, the director of seafood sustainability at the National Aquarium in Baltimore. It’s a problem because satisfying the sky-high demand has led to overfishing, one of the biggest threats to ocean ecosystems, and other environmental issues like habitat damage caused by irresponsible aquaculture practices and depleting wild fish supplies for fish meal.

You can help address these issues—especially today, on World Oceans Day—by diversifying your seafood habits. “Every time someone eats a piece of seafood that's not salmon, tuna, cod, etc., it relieves pressure on those wild fish stocks,” says Adam Geringer-Dunn, co-owner of sustainable seafood-focused Greenpoint Fish & Lobster Co. in Brooklyn. “Consumer demand directly impacts what species are targeted by fishermen.”

Tate recommends the handy EatTheseFish as a resource, but you can start with these five simple, sustainable suggestions that are just as (or more) nutritious than the fish you’re currently eating.

(1) Sardines

American consumers tend to prefer big fish at the top of the food chain, like tuna, halibut, and Chilean sea bass, but shifting to smaller types can make a big difference. “Large fish generally take a long time to reach maturity and reproduce, so they are very susceptible to overfishing,” Geringer-Dunn explains, while the small guys tend to be more plentiful. New York City-based nutritionist Rochelle Sirota, RD,recommends sardines, which are higher in omega-3s than most seafood and also contain lots of important vitamins and minerals. Bonus: “The small fish tend to be less polluted,” she says, with things like PCBs from plastics and mercury.

(2) Dogfish

This is among what fishermen call “bycatch,” or fish that is caught unintentionally in search for a more sought-after species. “There’s so much of it, and nobody wants it,” explains Michael Chernow, owner of popular sustainable seafood restaurant Seamore’s in New York City, where dogfish (which is actually a small shark) is a top-seller. Expect a white, flaky fish with mild, sweet flavor and a nice dose of brain-boosting nutrients like selenium and B vitamins.

(3) Mussels and Oysters

Sucking down raw oysters shouldn’t be an activity reserved for the occasional summer happy hour. Most shellfish is farmed, and unlike most fish farming, shellfish farms are often highly sustainable. “Mussels and oysters in particular naturally filter and clean waterways, and create nurseries for juvenile fish,” Geringer-Dunn says, and they also don’t require feed, since they filter phytoplankton directly from the water. Oysters are a terrific natural source of a host of minerals as well as vitamin B12.

(4) Pollock

Both Alaskan and Atlanticpollock are sustainable, high-protein choices, and they’re perfect to replace varieties like cod or haddock in recipes that call for white, flaky fish. Tate offers that idea as an overall tip, too: remember that you can always substitute a similar, more sustainable option when cooking. “A recipe does not need to call for haddock, pollock, or cod,” she says. “It can just say, ‘white flaky fish of your choice.’ This allows us not to put so much demand on a fishery.”

(5) Porgy

Porgy, also known as scup, is plentiful off the East Coast, so overfishing is not an issue. And Tate says that its flavor, which is similar to snapper, is a must-try. “Porgy is absolutely fabulous and the majority of seafood consumers have never enjoyed this amazing fish,” she says.