The rather alarmingly named condition “hole in the head” is a disease that can affect both goldfish and tropical fish, and is often the result of keeping your goldfish in poor-quality water over a prolonged period of time, either due to an overcrowded tank, insufficient cleaning, or water changes that are too infrequent.
Read on to learn more about hole in the head, plus what you can do to help your goldfish if they are afflicted with this condition.