A Hobart marine police spokesperson said a commercial fishing boat has been seized and the man have been charged with offences which allegedly caused "significant cost to the fishery".

"Police will allege the fishermen were misreporting catch, fishing inside marine reserves, retaining under size Rock Lobster and unlawfully selling Rock Lobster.

"The complex and lengthy police investigation culminated this week with the charge of trafficking in fish under the Living Marine Resources Act 1995 laid against the men.

As well as the North-West man, a 29-year-old Seven Mile Beach man and a 26-year-old Sandy Bay man who were both commercial rock lobster fishermen.

The three men were bailed to appear before the court in February.

A 15-metre boat was seized, but has been returned under stringent conditions.

"Police wish to remind members of the public and businesses that with the Rock Lobster season about to commence, legally seafood can only be purchased from approved fishermen, wholesalers and retailers," the spokesperson said.

"Receipts must be obtained and in the case of purchased Rock Lobster tags must he attached to the fish. Serious fines and special penalties may apply.

Illegal fishing activity can be reported to Fishwatch on 0427 655 557.