Four men have been fined over $30,000 for a black market fishing operation, including the catch and unlawful sale of female and undersized blue swimmer crabs around Brisbane.

Two commercial fisheries will appear in Caboolture Magistrates Court in April, charged with 59 offences and fined over $29,000.

Minister for Agricultural Industry Development and Fisheries, Mark Furner, said the black market has a real potential to impact commercial fisheries and lead to unsustainable fishing practices.