Goodbye, tuna. So long, cod. Hello, pangasius and kelp!

These are the seafoods — and sea organisms — we are likely to be eating in the future.

(Shrimp, don't worry. You'll always be our No. 1.)

At the same time that ocean resources are hitting their limits because of climate change, pollution, and overfishing, consumer demand for seafood is increasing. To reconcile these opposing trends, we not only need to change which fish species we're eating but also how we manage wild-caught and farmed foods from the sea.

So says Paul Greenberg, a fishing-industry expert and the author of two books about the future of the oceans, "Four Fish" and "American Catch."

Traditional fisheries and aquaculture, a term for breeding and harvesting fish in the ocean or other bodies of waters, are built around large predatory fish, such as tuna and salmon.

Click to enlarge. Mike Nudelman/Business Insider

Greenberg, a fellow at the Blue Ocean Institute, says we need to reorganize our "seafood pyramid" to promote filter-feeders such as seaweed and shellfish, which are easy to harvest, fast-growing, and help to clean the ocean by sucking up harmful pollutants.

Greenberg predicts that in 20 years a brown variety of seaweed called kelp will rank as one of the top 10 most consumed seafoods in America. "If I could buy kelp futures, I would," he says.

Certain species of whitefish that are better adapted for aquaculture environments, like tilapia and pangasius, will knock tuna and salmon down the list, especially as those fish become more expensive as stocks tank.

Aquaculture 2.0

Aquaculture gets a bad reputation, mainly for environmental reasons, but it isn't bad if it's done right, says Greenberg.

That means moving away from large-scale aquaculture systems that pollute the open ocean and instead farming animals and plants that do well in small plots of ocean. That includes bivalves like clams, mussels, and oysters and edible seaweeds like kelp.

"If aquaculture were organized around this principle, then it would be good for the country," says Greenberg.

Bren Smith of Thimble Island Oyster Company grows kelp and shellfish on a small-scale ocean farm in Long Island Sound. TedTalk

Bren Smith of Thimble Island Oyster Company, and owner of the second-largest kelp farm in the country, calls this type of ocean farming aquaculture 2.0.

Smith has pioneered an aquaculture system that "restores rather than depletes the ocean." Smith raises seaweed and shellfish together on a 20-acre underwater farm in Long Island Sound. Kelp and mussels are grown on floating lines that are attached to the sea floor by anchors. Below that are cages of oysters and clams.

This method requires very little gear (no trawls or pens) so it isn't environmentally destructive. The system is also self-sustaining because the kelp and shellfish feed themselves by straining food particles from the water. They also help the ocean by removing nitrogen — a nutrient that can lead to harmful algae blooms — from the water.

"In 20 to 30 years, kelp is going to be the cheapest food on the planet," says Smith.

Despite Smith's optimism, the expansion of kelp farming faces a couple of barriers. Although the superfood is coming along with Asian cuisine and increasingly served in salads and soups and sold in U.S. grocery stores as a dried or roasted snack, seaweed still isn't appealing to the American palate.

Kelp fettuccine with crab and uni butter. Thimble Island Oysters Smith is trying to change America's taste preferences by teaming up with restaurants in New York City to work kelp into foods that are already popular, including kelp butter and kelp fettuccine.

The Rise Of Whitefish

The whitefish market, generally recognized as all those species that would end up in a fish stick or fish sandwich, used to be thought of as mostly Atlantic cod. But with cod on the brink of collapse and climate change driving the rise in ocean temperatures, warm-water species will be favored over cold, says Greenberg.

Tilapia and pangasius, already the fifth- and sixth most-consumed fish in America, respectively, will assume a greater portion of the market since both are nearly 100% farmed today. "I could see them going up a notch or two," says Greenberg.

The air-breathing pangasius, marketed as basa, swai, or tra in the U.S., is a particularly good choice for aquaculture because it can tolerate crowding by sticking its mouth above the water to get oxygen.

Greenberg helped us imagine what a list of the top 10 most-consumed seafoods might look like 20 years from now. Business Insider

Asian carp, a large fish that's taking over Midwestern rivers — and menacing the Great Lakes — is already widely consumed in China. It could move onto the list depending on consumer acceptance. Regardless of the uproar over the Asian carp infestation, says Greenberg, "The biological argument for carp is really hard to resist." Carp are feed-efficient and can easily be worked into a polyculture system, the practice of growing more than one aquatic species in the same pond. For instance, China was one of the first countries to raise carp, ducks, and rice all together.

But the fast-growing fish are still a hard sell in America. For one thing, carp is very bony, making it tough to filet and eat. Americans seem to struggle more with gnawing their way around bones than the Chinese do, says Greenberg. Maybe we'll "come up with some giant, horrible machine called a carp-masher," he jokes.

Tastewise, Americans might be more receptive to cobia, a flaky whitefish with a sweet, rich flavor that has huge commercial potential in the aquaculture industry, according to Greenberg. China is the leading producer of farmed cobia, but production will likely expand to other nations in the future, according to the National Ocean and Atmospheric Administration.

The seafood we eat in the future will ultimately be influenced by a combination of what's left in the ocean and the ethical decisions we make about what's good for the environment. "If we don't have a choice, we'll naturally gravitate toward cheaper and more efficient foods like carp and seaweed," says Greenberg.