Skin and fins · Updated 2026-09-21

Fin rot in aquarium fish

Progressive fin damage associated with bacterial infection, commonly enabled by injury, stress or poor water quality.

Prompt veterinary attentionFreshwater fishFish

Veterinary care setting for freshwater fish and fish

Visual guide to warning signs including breathing difficulty, appetite loss, vomiting, mobility change, abnormal droppings and collapse — Changes in breathing, appetite, movement, digestion or alertness can need veterinary assessment. Collapse and breathing difficulty are emergencies.

Signs to watch for

Frayed fin edges
White or red fin margins
Fin loss
Hiding
Reduced appetite
Rapid breathing

Causes and risk factors

Ammonia or nitrite exposure, unstable conditions, aggression, injury and crowding can damage tissue and permit opportunistic infection.

How veterinarians diagnose it

Water testing and examination of the whole group are essential; microscopy or culture may be needed because trauma and parasites can look similar.

Treatment and management

Correct water quality and aggression first. An aquatic veterinarian can advise whether supportive care, salt or an appropriate antimicrobial is indicated for the species and system.

Prevention

Cycle aquariums fully, test water routinely, quarantine additions and provide compatible stocking and cover.

Outlook

Usually good before infection reaches the fin base or body; systemic disease is more serious.