"I knew it was a tiger trout, but until I got back to the motel I was staying at and Peter the owner told me how rare they were, I didn't know how lucky I was to catch one."
Mr Roberts said he released the fish back into the stream, as he did with all of the trout he caught.
I get as much pleasure in catching them as I do in putting them back.
He said he used a corxia-style fly, similar to a water boatman, to catch the trout, which he photographed and sent to local Fish & Game staff.
"It was a lot of fun and the fishing here has been excellent. The fish you get here are much bigger than what we get in England, I'll definitely be coming back," he said.
Eastern Region Fish & Game Officer Mark Sherburn said it was indeed a very rare catch.
"We don't release any tiger trout to the Ngongotaha Stream so the only way it could have got there is that it has escaped from one of our hatchery ponds.
"It's the first time I've heard of one being caught in there. They are raised at Ngongotaha and we only release them into Lake Rotoma."
Mr Sherburn said tiger trout were not naturally occurring as they were a hybrid cross between brown trout and a brook trout. They are also sterile, so they can't breed.
"It's extremely rare to have this happen," he said.