If you'll look closely at the left side of this catfish's mouth, you will see a small red sore. This is where, while kissing this fish, Theo got mad because the cat was not reciprocating the loving tongue swirl. Hence Theo bit the fish.
They are not friends anymore, and this catfish has initiated a harassment lawsuit.

There is a legal defense fund started for Theo entitled "I just wanted to love you" c/o Jaegerwald Milk & Spice Company, Central OH.