Freshwater aquarium fish can be susceptible to various diseases. Here are some of the most common diseases that can affect freshwater fish:

Ich (Ichthyophthirius multifiliis):

Also known as “white spot disease,” ich is characterized by white spots on the fish’s body and fins. It’s caused by a parasitic protozoan and is often accompanied by flashing and lethargy.

Fin Rot:

A bacterial infection that causes the degradation of fins and tail. Infected fins appear frayed and may have a disintegrating appearance.


A symptom of organ failure or bacterial infection, dropsy leads to the fish’s abdomen swelling due to fluid accumulation. Scales may also stick out, resembling a pinecone.

Columnaris (Flexibacter):

This bacterial infection causes lesions on fish, especially around the mouth and fins. Lesions may appear cottony and white.

Velvet (Piscinoodinium):

Similar to marine velvet, freshwater velvet is caused by a parasitic dinoflagellate. It appears as a fine golden or rust-colored dust on fish.


Fungal infections can appear as cotton-like growths on fish. They usually develop on wounds, injuries, or stressed fish.

Anchor Worms:

Parasitic crustaceans that attach to the fish’s body, causing irritation, inflammation, and possible infection.


While not a disease, constipation can affect fish health. It causes bloating and can lead to swim bladder issues or impaction.

Hole in the Head Disease:

Also known as Hexamita or HITH, this condition causes pitting on the fish’s head and body. It’s often associated with poor water quality and nutrition.

Cotton Wool Disease (Saprolegnia):

Another fungal infection that results in a cotton-like growth on fish, often affecting wounds or damaged areas.

Preventing and managing these diseases involves maintaining good water quality, providing a balanced diet, and minimizing stress. Quarantining new fish before introducing them to the main tank can help prevent disease outbreaks. If you suspect your fish are ill, it’s important to diagnose and treat the issue promptly to prevent further spread and complications.