Atlantic Tomcod

The Atlantic Tomcod, also known as frostfish or tommy cod, is a benthopelagic piscivore. It is common in the seacoast region, though locals claim large ones are caught less often in estuarine rivers than they once were. Juveniles are occasionally collected during trawl and fyke net surveys.

Dependence Upon Estuaries

Adult Feeding — Very Important
Juvenile Feeding — Very Important
Refuge/Shelter — Very Important
Passage — Very Important

Life History

Atlantic Tomcod are anadromous, but they do not travel far between salt and fresh water. Spawning occurs in shallow brackish or fresh water over gravelly bottoms and sand. Eggs sink to the bottom in masses. Incubation takes 24 to 30 days at temperatures of 30 to 43ºF (4 to 6ºC). Newly hatched larvae swim to the surface within 24 hours of hatching to gulp surface air before their pneumatic duct closes. Young-of-the-year may remain in fresh or slightly brackish water for their first spring and summer, but then move into estuaries and nearshore waters.

Habitat

Atlantic Tomcod frequently inhabit the mouths of streams or estuaries. Sometimes they are found in salt marshes. Young-of-the-year and small adults are often found in shallow eelgrass beds. Tomcod are resistant to sudden changes in temperature and salinity.

Food Web Position

Food

Mostly copepods as larvae, then small crustaceans, small mollusks, worms, and fish larvae. Also eat their own eggs, larvae, and juveniles.

Predators

Striped Bass and Bluefish

Fisheries

A good tasting fish, but no longer plentiful enough to support a commercial fishery.

Calendar

Migrate Upstream

October and November

Spawn

November through February, peaking in January

Migrate Downstream

February to May; later for young-of-the-year

Northwest Atlantic Range

Southern Labrador to Virginia

Points of Interest

Atlantic Tomcod populations have been reduced due to loss of access to spawning grounds, overfishing, and exposure to toxins. Because they typically live year-round in estuaries, tomcod are particularly subject to stresses from pollutants.

Tomcod produce antifreeze proteins that enable them to tolerate water temperatures below freezing, leading to their “frostfish” moniker.

Appearance

Average 9 to 12 in (23 to 30 cm)

Atlantic Tomcod closely resemble Atlantic Cod but have rounded tails and small eyes rather than square tails and large eyes. They have a pale lateral line slightly arched over their pectoral fins. Coloring on the back is olive or muddy green, fading to lighter on sides and mottled with dark blotches. The belly is gray or yellow-white.