White spot disease (Ich)

What is it?

White spot disease (Ich) is a very common parasitic infection in aquarium goldfish, caused by a microscopic protozoan parasite. It causes the appearance of small white dots on the skin, fins and gills. It is one of the most common and contagious diseases in the aquarium trade.

Commonly observed signs

These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.

Causes and risk factors

The disease is caused by a microscopic ciliated parasite that settles under the fish's skin to feed. It thrives particularly well when the water in the aquarium is of poor quality or when the fish is weakened. The parasite's life cycle includes a free-living phase in water that is highly contagious.

Stress linked to a change in environment, poor water quality, sudden temperature variations and overcrowding in the aquarium increase the risk. Newly introduced fish without a quarantine period are particularly at risk. A weakened immune system also favors the development of the disease.

Transmission

The parasite is easily transmitted from one fish to another through contaminated aquarium water. The introduction of new infected fish, plants or undisinfected equipment is a common source of contamination. The parasite multiplies quickly in a confined environment such as an aquarium.

Diagnosis and care

Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.

Prevention

References

MSD Veterinary Manual

Content reviewed by the TunisieVet editorial team · Updated 18 August 2026