A Hamilton student has caught a 203.7kg blue marlin in the Bay of Islands and won $50,000.

Using a 37kg rod and reel on a Pakula lure, the 13-year-old was on a boat with three other anglers, including his father.

Nobody else could touch the rod or he would be disqualified.

Dylan's father Scott White said the fish surfaced about 30 times "going crazy" during the 38 minutes from hook up.

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"Skipper Chris Brittain then backed up the boat continuously in 3.5 metre swells, as we applied more drag and Dylan began retrieving line we all got very wet with the sea breaking over us," he told Fairfax.

Dylan was the only junior to enter the Caribbean Zane Grey International Game Fishing Tournament and the youngest winner.

The $50,000 prize money will go into a savings account until Dylan is old enough to know what to do with it.