Ickle baby goldfish
Working at an aquatics store, an older gentleman came in with a little fish in a pickle jar. They had been appearing in his pond all summer, and he did not know what they were. He said he had asked in another pet shop and they didn't know.
It was an easy one, instantly knew it was a baby goldfish. As thanks for the ID (and advice setting up a rearing tank for them) he let me have the little guy ^_^.