The eulachon (/ˈjuːləkɒn/ (Thaleichthys pacificus), also spelled oolichan /ˈuːlɪkɑːn/, ooligan /ˈuːlɪɡən/, hooligan /ˈhuːlɪɡən/), or the candlefish, is a small anadromous species of smelt that spawns in some of the major river systems along the Pacific coast of North America from northern California to Alaska.

The name "candlefish" derives from it being so fatty during spawning, with up to 15% of the total body weight in fat, that if caught, dried, and strung on a wick, it can be burned as a candle.

It forms an important part of the diet of many ocean and shore predators, and serves as a prominent food source for people living near its spawning streams.

Eulachon, as anadromous fish, spend most of their adult lives in the ocean but return to their natal freshwater streams and rivers to spawn and die.

[clarification needed] Indigenous communities of the Pacific Coast from California to Alaska made eulachon an important part of their diet, as well as a valuable trade item with peoples whose territories did not include spawning rivers.

[14] On March 16, 2010, NOAA announced that the Southern DPS of eulachon will be listed as threatened under the ESA, effective on May 17, 2010 (See: the Federal Register notice published on May 18, 2010, at 74 FR 3178).

[19] Overall, the species faces multiple threats, including overharvest, pollution, loss of freshwater spawning habitat due to logging, diversion and dam construction and climate change.

[1][2] Canadian spawning runs have been severely depleted compared to historic levels,[18] while abrupt declines were reported in the Columbia, Fraser and Klinaklini rivers in 1994.