Crayfish cage

Crayfish Cages are Fishing items used to catch Crayfish. They can be bought for a few coins at the Grand Exchange or at Gerrant's Fishy Business (run by Gerrant) in Port Sarim. There is no bait needed to use crayfish cages, and many fishing spots for crayfish around RuneScape. Many players do not use crayfish cages, for crayfish only heal 20 life points, and even shrimp heal more health. Crayfish cages look relatively similar to lobster pots, although they are very different. Crayfish aren't seen often on member worlds, though. You can also get a crayfish cage for free or 20gp from Hank in lumbridge.

First Fish
Crayfish are one of the first fish new players will catch. This means that Crayfish cages are very popular in free to play worlds, but you will not get very many coins for them.

Where to Find
Crayfish cages can be used wherever there is a fishing spot with the "Cage" spot available. There are quite a few of these in F2P, though one of the most popular can be found north of Lumbridge Castle, at the pond near the mill. Another bonus of this spot is its proximity to the fishing store in Lumbridge.

Trivia

 * Crayfish cages used to be available from the Fishing Tutor but due to the Advisors and Objectives update he has been deleted. You can still get them for free in the Lumbridge fishing shop. If you take the free sample and try to sell it back to the shop, the shopkeeper will thank you for returning the sample but give you no money. Oddly enough, right below the free cage is a 10gp buyable cage.
 * It can also be used in Dragon Slayer when trying to get the map piece in the Dwarven Mines, as it is a small crustacean cage.