Me. Rev. Stat. tit. 12, § 12611

Except as otherwise provided in this Part, a person who takes a fish, other than baitfish or smelt, from inland waters pursuant to this Part shall immediately release that fish alive into the waters from which it was taken or immediately kill that fish. Any fish killed pursuant to this section becomes part of the daily bag limit. A person who possesses a fish in violation of this section commits a Class E crime.