In the default state, the goldfish swims around his tank.  He moves laterally, plunges vertically, and switches direction every so often.

When fish food is fed to him (by touching the rim of the TetraFin to the rim of the fish bowl), red and yellow LEDs light up in sequence to simulate fish flakes falling into the bowl.

The fish recognizes that food has been delivered, and heads upward to claim the goods.
He then spends some time consuming the food.
He is shown here with his mouth open.  The mouth opens and closes multiple times during each feeding cycle.
Usually, the fish resumes regular swim after each feed.  However, like a real fish, in the case that too much food is fed to him in a short period of time, he dies.  This is a picture of his corpse floating belly up. 

MAS.110 Spring 2002