In the case of fish, taste buds are not limited to the tongue or the mouth area but they can be found on the other parts of their body.
They have the ability to taste their food without actually swallowing it.
Proper functioning of the taste buds require moisture and the fish is always surrounded by water all time. Therefore, their external skin is always moist and have taste buds on their body.
The catfish has the highest number of taste buds (about 680,000) compared to other animals. Even humans have only 5,000 taste buds in their mouth.