Owning a ... goldfish
At the vet
Icthyophthirius: A tiny parasite which spreads all over the flesh and looks like a covering of salt. The fish's immune system will generally ward them off but if the fish is stressed (due to poor water quality/food or an aggressive tank-mate etc.) the immune system will break down, leaving the fish susceptible to many diseases. If your fish is infected, stop feeding and gradually raise the temperature of the tank to 85 Farenheit. This speeds up the lifecycle and eradicates the cyst. When the spots have gone, gradually lower the temperature again.
Anchor Worms: Anchor worms are visible parasites with bodies the shape of anchors. They have to be physically removed. Take the fish out of the tank and hold it in a wet cloth. Use tweezers to grip the worm at the base, near the point of attachment, and pull firmly and quickly. Treat the site of attachment so as to prevent infection. Put the fish back as soon as possible. Treatments are available.
Dropsy: A fish infected with this disease is bloated and looks about to burst. The scales become raised. Remove the infected fish to a quarantine tank. It is often caused by poor water conditions.
Fin Rot, fungus and velvet: are also caused by poor water conditions. Fin rot affects the dorsal fin, whereas fungus can affect the whole body. Treatments are available.
Swim Bladder disease: The swimbladder is an internal organ which allows fish to remain bouyant. It is filled with gas, the volume of which depends on whether the fish wants to swim at the top of the tank or stay down at the bottom. Symptoms include floating to the top of the tank, listlessness, and turning upside down. There are several causes, including a sudden temperature drop, bacterial infection and genetic disorders. Most commonly the cause is incorrect feeding. Blocked intestines can contribute to swim bladder disorders. It is sometimes a good idea to add some salt to the aquarium (this helps the fish's osmoregulation, the process by which oxygen is passed through the gills) over a 12 hour period. Fast the fish (stop feeding it) for 4 days to allow it to clear the blockage. Once it is clear, the swim bladder should return to normal. Resume feeding after the fourth day.