Red Spot Disease (Aeromonas skin infection)

About this condition

A condition in which reddish spots or patches appear on the body surface, often associated with bacterial infection by Aeromonas species. Fish weakened by poor water quality or stress are more susceptible.

Common symptoms

• Reddish spots or patches visible on the body surface
• Scales may lift or fall off around affected areas
• Reduced appetite; fish tends to rest near the bottom
• Lesions may progress to ulceration or tissue erosion

Common causes

• Immune suppression caused by poor water quality (ammonia/nitrite accumulation)
• Secondary bacterial infection by Aeromonas or similar species
• Physical injury from handling or overcrowding
• Stress from sudden changes in water temperature

Prevention (husbandry & daily care)

Maintain low ammonia and nitrite levels through regular water changes and substrate cleaning. Avoid overcrowding and quarantine new fish in a separate tank before introducing them to the main aquarium.

Related species guide

When to see a vet

What can a specialist store do?

Specialist aquarium retailers are often the most accessible resource, as veterinary practices experienced with medaka are limited. A specialist can assess the condition, recommend water quality adjustments, and advise on appropriate isolation protocols.

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