The northern spearnose poacher (Agonopsis vulsa), also known as the window-tailed sea-poacher or the windowtail poacher, is a fish in the family Agonidae. It was described by David Starr Jordan and Charles Henry Gilbert in 1880, originally under the genus Agonus. It is a marine, temperate water-dwelling fish which is known from the eastern Pacific Ocean, including southeastern Alaska to southern California, USA. It dwells at a depth range of 0 to 163 metres (0 to 535 ft). Males can reach a maximum total length of 20 centimetres (7.9 in).

The northern spearnose poacher is sometimes used as a public aquarium fish.

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