Fin Rot, Dropsy, and Velvet: Recognizing Common Fish Diseases

While ich gets most of the attention, several other diseases are common enough that every fishkeeper should know how to recognize the early signs.

Fin Rot

Fin rot appears as ragged, discolored, or disintegrating fin edges, usually caused by poor water quality or secondary bacterial infection following an injury. Improving water quality and, if needed, a course of antibacterial medication typically resolves it.

Dropsy

Dropsy causes a swollen abdomen and raised “pinecone” scales, and is actually a symptom of internal organ failure rather than a single disease itself. Unfortunately, by the time symptoms appear, prognosis is often poor, making prevention through good water quality essential.

Velvet

Velvet appears as a fine, gold or rust-colored dust coating the body and is caused by a parasitic dinoflagellate. It spreads quickly and is often treated similarly to ich, sometimes combined with darkening the tank temporarily since the parasite relies partly on photosynthesis.

Prevention Is the Real Cure

Nearly all these diseases are triggered or worsened by poor water quality and stress. Consistent testing (see Understanding Aquarium Water Parameters) and a proper quarantine routine prevent the majority of outbreaks before they start.