From this story on the Huffington Post:
A fish raised on Kit-Kats is being forced to give them a break after getting too big for his tank. The fatso fish is named Gary, and he's a 15.7-inch, 8.8-pound gourami, an exotic Asian freshwater fish that is considered a delicacy in Indonesia. Gary was in the care of a private owner until he was donated to the SeaLife Aquarium in London after becoming too large, a common fate for many domesticated fish, according to center spokeswoman Rebecca Carter. However, despite being supersized, Gary was not eating the normal aquarium fare he was being served. Officials were perplexed until they checked with the previous owners and discovered he had been raised strictly on a diet of Kit-Kat candybars. "I have never heard of a fish being fed chocolate, let alone being brought up entirely on the stuff," Carter said in a statement on the aquarium's website. "Gouramis usually eat a diet of fruit but Gary doesn't appear to have suffered any ill effects from his chocolate addiction. However, we would NOT recommend feeding fish confectionary of any kind!"