Is it fatal if goldfish get spots on their tails?

While spots on a goldfish's tail may look concerning, they are not always fatal. Here are a few possible causes and their potential severity:

1. Ich (Ichthyophthirius multifiliis): Ich is a highly contagious parasitic disease caused by a protozoan. It typically appears as small, white spots or bumps on the fish's body, including the tail. Ich is treatable, but it can be fatal if left untreated, especially in severe cases.

2. Velvet (Oodinium pillularis): Velvet disease is another protozoan infection that causes tiny, gold or brown spots on the fish's skin and fins. It can be challenging to treat and may result in the fish's death if not promptly addressed.

3. Fungal Infections: Fungal infections, such as Saprolegnia, often appear as cotton-like patches on the fish's body, including the tail. These infections can be serious and may lead to tissue damage and organ failure if not treated effectively.

4. Bacterial Infections: Bacterial infections can also cause spots or lesions on the tail. Depending on the type of bacteria and the severity of the infection, it may range from mild to fatal.

5. Injury or Trauma: Occasionally, spots on the tail may be caused by physical injury or trauma, such as fin nipping, bumping into objects, or fighting with other fish. These spots are usually not fatal but may require proper wound care and observation to ensure they don't develop into secondary infections.

It is important to observe the fish closely, monitor its behavior and overall health, and seek appropriate treatment from a qualified veterinarian or experienced aquarist if the spots appear to be a result of a disease or infection.