How do you catch krabby in Pokemon FireRed?

It's only available in leaf green. use the good rod Actually YES you can catch Krabby in fire red, they' re just uncommon, and you catch them with good rods.
A Krabby is easiest to catch using a Good Rod. It can be obtained in Fuchsia City at the Fishing Guru's house. Nearby, at the beach south of Fuschia, about a fifth of the catches will be a Krabby. It can be caught at the edge of almost any water with waves that you are allowed to fish on. Using a Super Rod to catch a Krabby in FireRed is very difficult, if not impossible. In FireRed at least, they are generally level 6-15, too weak for a Super Rod.