Apparently they can! That is if they only eat chocolate-covered wafers! That is exactly what had happened to Gary, giant gourami at the the Sea Life London Aquarium. Gary weighs an astounding 8.8lbs and is thought to be seven to ten years old.
Gigantic Gary refuses to eat ordinary fish food. His previous owners said that they only fed the fish with Kit Kat chocolate covered wafers. They needed to donate Gary to the aquarium facility because he already outgrew his tank.