Raw Fish

Raw fish is a food item which is obtained by fishing.

Fishing
The most common way of obtaining raw fish, like any other fish, is fishing. The chance of one being caught can be increased with the 'Lure' enchantment.

Guardians
Another method of obtaining them is through defeating Guardians. This method can be very efficient if a Guardian farm is built.

Food
Raw fish restores and 0.4 saturation. Eating raw fish is not efficient though, as you can cook them into cooked fish, which restores and 6 saturation.

Taming mobs
Raw fish can be fed to ocelots to tame them.

Trivia

 * In the Halloween Update, Notch said he would add fish as a sea creature; however, he had limited time, and was thus only able to add them as an item.
 * Raw fish most closely resembles white crappie or tilapia. However, the texture files and language text label them as cod.