"We are not giving away too many secrets to say that he was trolling a fluoro Tassie and a smelt fly, which is what the fish took," Osborne said.
The angler had considered releasing the fish before he spotted the tag.
"We urge all anglers entered to take care to check all legal-size fish that they catch for the three-centimetre-long tags, which are attached just behind the fish's dorsal fin."
"We encourage you to make the most of the good weather before a cold snap that's forecast and not give up fishing as there are still 29 potential winners out there to be caught."
Osborne said it was worth reminding anglers that aside from the big prize, there was an outboard from Telfer Marine to be won, along with voucher or tackle prizes worth $250 apiece, thanks to local firms Hamills, Kilwell and Outdoorsman Headquarters.
"Every orange tag will at least win a voucher or tackle prize."
The orange tags must be presented in person to staff at Fish & Game Eastern Region's office at 1130 Paradise Valley Rd, Ngongotahā, by 1pm on Monday.
Anglers who catch trout with the normal yellow Datawatch tags either during, or after the promotion has finished, are also potential winners as they go in the draw for a free fishing licence at the end of the season.