A Flatfish for All Seasons

By Henry S. Parker

In the depths of winter, when seawater congeals with cold, some Chesapeake Bay denizens thrive. One is the appropriately named Winter Flounder, Pseudopleuronectes americanus. 

Winter Flounder have an “antifreeze” compound that allows them to tolerate icy waters. More about that adaptation later, including its potential commercial applications. First, some background about these fascinating fish.

Winter Flounder are not just cold weather creatures. You can find them year-round along North America’s East coast from the Gulf of St. Lawrence to North Carolina. U.S. waters harbor three different stocks: the Gulf of Maine; Georges Bank; and Southern New England/mid-Atlantic. The fish typically nestle in seabed sediments with both eyes protruding from the upper, right side of the body (a configuration that enhances their vision of overlying waters). Their dark, sometimes mottled upper bodies blend in with their surroundings. Their underbodies are white. 

Also known as Blackback, with an average weight of four to five pounds they’re a popular commercial and game fish. Undisturbed they live 15-18 years. They spawn close to shore during the winter and spring. Females carry a million eggs or more, depositing these multiple times on the seabed. There the newly hatched larvae develop. As they mature into juveniles, one eye migrates to join the other on the flounder’s upper surface. Age to maturity depends on water temperature. In Chesapeake Bay it takes two to three years.

Winter flounder are omnivorous but prefer invertebrates, plankton, and little fish. Their small mouths limit the size of their prey. In turn, they’re consumed by other fish species, seals, predatory birds, and, in their larval stages, even jellyfish. They’re also affected by parasites, habitat disturbance by humans, and pollution. Government fishery managers believe that populations are “sustainably managed,” but warming waters from changing climate may be contributing to recent population declines.

Now, about that “antifreeze” attribute. Two different biomolecules in winter flounder prevent their blood from freezing in low seawater temperatures. Known as “antifreeze” plasma proteins (AFPs), these compounds inhibit the growth of ice crystals in body fluids when the surrounding seawater is cold enough to freeze (approximately minus two degrees Celsius). Though other cold water fish species also have AFPs, as well as certain plants, insects, and microorganisms, they were first described in winter flounder. 

The discovery of AFPs did not go unnoticed by agricultural and biomedical concerns. These industries recognized potential applications to extending harvest seasons by improving frost resistance; increasing frozen food shelf life; hypothermia therapy; cryosurgery; and cryopreservation of human tissue (and even human bodies). 

This is not the stuff of science fiction, nor even a distant pipe dream. We’re already experiencing some of it. Did you know that your favorite ice cream or yogurt may contain AFPs isolated from cold-water fish and replicated in genetically modified yeast – with the approval of FDA? Before you recoil in horror, know that fish-based genetically modified organism (GMO) technology is also used in the production of insulin and that, according to scientific consensus, it’s safe (nontoxic and nonallergenic). 

Still, wider adoption of AFPs in food and medicine will require overcoming the challenge of public resistance to GMOs. Compelling, detailed, accurate, and accessible studies are essential. Two examples, one relating to winter flounder, underscore this. 

First, remember the Flavr Savr tomato? Calgene (now part of Monsanto) commercialized this genetically-engineered product in 1997 to improve shelf life. FDA approved it, the first GMO food to receive this distinction. But the rollout triggered virulent protests, including charges that the product was unsafe. Perhaps, fortunately for wary consumers, efforts to market the fruit died on the vine. Calgene blamed the failure on problems with product quality, production schedules, and marketing, but public opposition to GMOs and inadequate safety studies were important factors.

The second example is Monsanto’s 1990s-era incorporation of the winter flounder AFP gene into tomato plants, to improve the fruit’s frost-hardiness. When anti-GMO forces got word, they mobilized against this “fish tomato.” Monsanto never marketed the product.

So the poor winter flounder has come into some bad press. But, depending on the evolving science and future public perceptions, its AFP gene may yet have a bright future in the food and biomedical industries. Regardless, it will always be first-rate dinner-plate fare.

Henry “Hank” Parker is a scientist and writer who previously lived in Annapolis but now resides in Vermont.