An Australian fisherman got the surprise of his life after hauling in a mammoth bluefin tuna thought to be radioactive.

Victorian fisherman Paul Worsteling reeled in a monster bluefin tuna 50km off the coast of Greymouth, New Zealand.

It took a two-hour battle using 58kg of tackle to land the 2.7m beast, estimated to weigh more than 275kg.

Worsteling, a host of Channel 10's IFishTV, invited scientists from New Zealand Fisheries on a chartered vessel to explore this pocket of ocean, which yields 170,000 tonnes of blue grenadier each year.

The freakish fish will be tested for radiation to help determine if fish schools affected by the Fukushima reactor meltdown in Japan have migrated around the world.

The crew reportedly enjoyed a few slices of sashimi and anything the scientists didn't use for research was delivered to a smoke house.

It's believed the fish would be worth as much as $713,000 in Japan.