MPI staff seized 4 vehicles and a small boat yesterday as they lifted the lid on black market fish network in Christchurch and North Canterbury.
Thirty staff executed 19 search warrants including the premises of 6 commercial retailers.
Six principal people have been interviewed and staff are interviewing a further 20 people.
Those involved may face Fisheries Act charges of illegally buying, selling or possessing fish to obtain a benefit. These charges carry a maximum penalty of a $250,000 fine and 5 years in prison.
MPI Southern Compliance Manager John Slaughter says the operation followed an investigation into black market trading in paua and rock lobster in Canterbury and included the use of an undercover officer to infiltrate and determine the scope of the market.
Mr Slaughter says the extent of the operation and the demand for black market fish is disturbing.
"It is disappointing that this trade can develop so easily and we need to appeal to the public to be vigilant about the illegal fish trade. It is illegal to sell fish outside commercial fishing ventures and likewise to buy fish.
"Bargain priced fish is likely to have come from an illegal source. If people have suspicions we ask they report this to the 0800 4POACHER hotline (0800 4 762 243).
"This illegal take and trade of fish undermines the ability to manage stocks and depletes accessible amateur fishing spots, which deprive those legitimate fishers and future generations of their entitlements."