— (Atlantic tomcod, Tomcod, Frostfish, Tommycod), is a type of cod found in North American coastal waters from the Gulf of St. Lawrence, Estuary of St. Lawrence River and northern Newfoundland, south to Virginia.

[2] In 1757, Count Louis-Antoine de Bougainville (1729-1811) noted that the French settlers of New France practiced angling under the ice to capture the Microgadus tomcod Walbaum which swims upstream to spawn in the streams flowing into Lake Saint-Pierre and its tributaries, near Trois-Rivières.

[2] A bimonitoring program tracked hormone levels of Atlantic tomcod caught near Miramichi and Kouchibouguac in 1993 and 1994, demonstrating that the preparatory period for spawning began in September[5] with maximal steroid levels in November, and spawning took place from late December to January.

After General Electric dumped polychlorinated biphenyls (PCBs) in the Hudson River from 1947 through 1976, tomcod living in the river were found to have developed an increased resistance to the compound's toxic effects.

Scientists identified the genetic mutation that conferred the resistance, and found that the mutated form was present in 99 percent of the tomcods in the river, compared to fewer than 10 percent of the tomcods from other waters.