Sick Goldfish

One of my goldfish has become listless and uninterested in food this week. He just lies on the bottom of the tank while the other goldfish dash to the top of the tank. There is nothing obviously wrong with him--his color is good, his eyes keep track of what's going on around him, he swims away when another fish pesters him--he just isn't behaving like he used to.

After two days of him not eating, I started holding him and putting the flakes into his mouth for him. At first, he wriggled a lot, but now he just accepts it. He sees me approaching the tank and his goggle eyes follow my movements. Hopefully, he will be better soon.