What could cause a goldfish dorsal fin to collapse?

Answer by  sdblack99 (329)

Most common is high ammonia levels. Goldfish produce waste in the form of ammonia and it is toxic in high levels. You must perform frequent water changes depending on the size of tank or bowl, and use an additive like ammo-lock or any other ammonia detoxification agent.

Answer by  navywriter (790)

Your fish is sick, maybe due to overcrowding or some other disease that causes this. He might also have a parasite.

Answer by  kirri (478)

The best place to start is to test the water in your tank. Fish are very delicate when it comes to water conditions. The next step to take would be to medicate for velvet a parasite that feeds off of the fishes scales.

Answer by  Mech79 (185)

If the tank is too small then the amonia levels will be too high on a regular basis and can cause the fish to have both external and internal issues.

Answer by  champaign9497 (11977)

Sometimes it's because the fish is getting to big for the tank that it is being kept in. If you are super worried go to your local fish store and tell them what size tank you have and how many fish you have in it and what has happened to your goldfish and they will be able to help you.