Ministry of Fisheries officers have closed the net on a black market fish ring operating in Southland.
Two commercial fishermen were detained early on Tuesday morning after a six-month investigation.
The ministry alleges the men have been supplying blue cod, rock lobster and oysters to the black market.
Southland district compliance manager Reece Murphy says the men, who operated from the port of Bluff, had been taking fish in addition to their commercially allowed catch.
Mr Murphy says it is uncommon for commercial fishing operators to be caught up in black market operations.
Mr Murphy says fisheries officers have identified some of the people who are thought to have bought the black market fish.
