Clownfish

Clownfish are food items that are obtained by fishing.

Fishing
The most common way of obtaining clownfish, like any other fish, is fishing. They are rare, as the chance of a catch is 2%. 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 is very inefficient, as the drop rate is roughly 0.05% (2.5 * 0.02).

As a food
One clownfish restores hunger and 0.2 hunger saturation.

Taming mobs
Clownfish can be used to tame ocelots, like most other fish.