Raw Fish

Raw Fish is a food item that can be obtained by fishing with a Fishing Rod in any body of Water. Unlike Mobs, they cannot be seen until caught. When using a fishing rod, it is best to fish on land with a large wall behind you, as when you reel the fish in, it flies out of the water and sometimes above your head. This happens more often when you are in a Boat as the boat lowers your height.

Raw Fish are cooked in a Furnace, much like Pork, into Cooked Fish. The raw fish heals one Heart and the cooked fish heals 3 hearts.

It is the most reliable fast source of food at the moment, as you do not have to wait for Pigs to spawn or for your Wheat to grow. Notch has mentioned that in the future there will be fish mobs, that were going to be added in the halloween update, but he only could add the item fish.