You do not need to catch a fish, if you already have one. Download the achievement world
https://www.dropbox.com/sh/68ihnr8ivz3jstw/AAC4bPQToqc06k9hk...Get a fish from the chest for taming an ocelet. Cook this fish in a furnace. Then make sure you r food bar is not at 100% (change to easy difficulty or higher and jump 5-10 times if it is at 100%), and then eat the fish.