Crystallised harpoonfish are fish that can be fished from fishing spots in Tempoross Cove. While fishing with a crystal harpoon, there is a 1 in 3 chance that players will catch a crystallised harpoonfish instead of a raw one.
During the fight with Tempoross, they are used as ammunition for harpoonfish cannons. Crystallised harpoonfish drains Tempoross' energy as much as raw ones, and cannot be cooked. While this means players will get fewer points over the course of the fight, players will instead receive 20% more Fishing experience from using them as ammunition.