"Go to an area where you can harpoon swordfish, tuna or sharks; the Fishing Guild and Catherby are good choices. Click on the harpoon spot as you would normally, but without a harpoon equipped or in your inventory, and you will catch a fish using your fingers as bait!" So as long as you are using a (bad) script that doesn't do a check for harpoon in inventory, then it's no different than normal tuna/swordfish/shark fishing.
source: http://2007.runescape.wikia.com/wiki/Barbarian_Training#Bare-Handed_Fishing