A group of Tasmanian fishermen believe they have caught in the biggest swordfish ever hooked in Australian waters by amateurs.

It took six hours for 16-year-old Kyle Longmore to reel in the 263-kilogram broad-bill swordfish while competing in the Coles Bay Classic fishing competition on the weekend.

Skipper Leo Miller said it was a gruelling battle.

"Mentally as much as physically. I think people don't realise [how gruelling it can be]" he said.

"Kyle was very physically exhausted but you've got to concentrate extremely hard for six hours in the sun [and] only get a little bit to eat and drink as people feed it to you while you're fighting.

"And these fish, they don't call them the gladiators of the ocean for nothing."

Mr Miller said they had no idea how big the fish was until they saw it jump.

"We didn't think the fish was all that big at first but then it came up and jumped and we knew it was a fair size because we got a pretty good look at it and it continued to jump for about three hours," he said.

"[It] jumped 23 times and we gradually just got closer and closer."

Anglers in Tasmania have an advantage in catching swordfish recreationally because of the close proximity of the continental shelf where the fish reside.

During the day swordfish swim down to depths of 600 meters but feed closer to the surface at night.