Rainbowfish

Rainbowfish is a consumable item obtainable from fishing.

Fishing
Rainbowfish can be obtained by fishing. In order to catch Rainbowfish, the player's hauling level has to be at least 90. Rainbowfish have a weight of 200.

They grant 11950 xp for the Hauling skill when caught.

Other methods
Rainbowfish can also be obtained by opening a Fish Case.

Usage
Rainbowfish is a consumable item, and can be consumed at any time by holding the use button while holding it. Rainbowfish offer minimal hunger and saturation but heals the player by health if consumed.

Gnawer
Rainbowfish can be fed to a gnawer. Feeding one to a gnawer will heal health to the player and do  damage to the gnawer.