Winter Flounder

(Pleuronectes americanus)

Winter Flounder

Distribution and Habitat

The winter flounder, also known as the blackback flounder, can be found from south Labrador and along the eastern seaboard of Canada and the USA as far south as Georgia. It lives inshore, in relatively shallow water (generally between 2 - 40 m depth), and can be found inhabiting soft muddy to moderately hard bottoms, although sandy bottoms are preferred. Young fish inhabit shallower water than older, larger ones. Some populations of winter flounder appear to undertake limited onshore-offshore migrations, moving offshore in winter and onshore in summer. However, they are tolerant of a wide range of temperatures and can be found in winter in the coastal waters of Newfoundland, in water temperatures as low as -1.8 degrees Celsius.


Winter flounder are sight feeders. They hunt mainly during daytime, and consume a variety of bottom-dwelling organisms including polychaete worms, bivalves, gastropods, and crustaceans. Flounder seldom exceed 45 cm in length, and most adults are in the 30 - 40 cm size range.

Antifreeze Production - Type 1 Antifreeze

Studies of winter flounder antifreeze production have been carried out with animals collected from Newfoundland and New Brunswick coastal waters. These animals spend their winters inshore in very cold icy waters and, consequently, are obliged to produce antifreeze or risk freezing to death. Onset of antifreeze production is under the control of photoperiod, with temperature playing a role in the level of antifreeze built up in the plasma and extracellular fluids during the winter.


Fletcher, G.L. 1981. Effect of temperature and photoperiod on the plasma freezing point depression, C1- concentration, and "antifreeze" in winter flounder. Canadian Journal of Zoology: 60, 348-355.

Fletcher, G.L., D.R. Idler, A. Vaisius, and C.L. Hew. 1989. Hormonal regulation of antifreeze protein gene expression in winter flounder. Fish Physiology and Biochemistry: 7, 387-393.

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