Can goldfish become depressed

Despite common mythology, Goldfish have a memory span in excess of 3 months and can distinguish between shapes an colour. Some goldfish are even able to learn tricks.

As the fulfillment of a fish's dreams are not communicable to humans, there is no point questioning whether a fish is feeling depressed. However, if you do find yourself asking the question, then interpret it as a reflection of guilt you may be feeling for mistreating a living creature (which was originally meant to be for your enjoyment) and make any necessary amendments to the way you look after your pet. With great power comes great responsibility!