Fish disease symptoms

Fish illness rarely appears without warning. Most outbreaks follow stress — poor water quality, temperature swings, overcrowding, or new arrivals skipping quarantine.

This section covers every fish symptom in our diagnosis catalogue. Match your fish below for photos, causes, and step-by-step treatment.

All symptom guides

• White spots (possible ich) — Salt-grain sized white spots on fins and body
• Clamped fins / lethargy — Fins held tight against the body, reduced activity or hiding
• Fin rot / fraying fins — Fins appear shredded, milky at the edges or shortening over time
• Cloudy eyes — One or both eyes appear hazy or white
• Bloating / pineconing — Swollen abdomen or scales standing out (pinecone appearance)
• Gasping at the surface — Fish repeatedly gulp air at the surface
• White fuzzy patches — Cotton-like white growth on mouth, fins or body
• Gold dust / velvet — Fine gold or rust-coloured dust on the body
• Bulging eye (popeye) — One or both eyes protrude from the socket
• Floating, sinking or swimming upside down — The fish cannot hold its position
• Open sores / ulcers — A reddened open wound with a pale eroded rim and missing scales
• Red streaks in fins or body — Fine blood-red streaks through the fins or reddened patches on the body
• Flashing / rubbing against surfaces — Fish dart and scrape their flanks against substrate or décor, often with rapid gill movement
• Pits or lesions on the head — Small pitted craters in the flesh above or behind the eye, often in cichlids and discus
• Thin or wasting away — Progressive weight loss with a sunken belly and visible spine despite the fish eating
• Cauliflower-like growths — Clustered white or grey nodules on fins or body resembling a cauliflower floret
• White spots on a marine fish — Fine white spots on a marine fish, often with flashing and rapid breathing
• Peeling mucus on a marine fish — Thick pale mucus sloughing away in patches with laboured breathing, classically in newly imported clownfish

General disease categories

• Bacterial infections
• Parasitic infections
• Fungal infections
• Marine parasites
• Viral diseases

Quick rules

1. Test water before medicating — ammonia and nitrite must be zero.
2. Quarantine new fish — the cheapest insurance in the hobby.
3. Log symptoms and parameters — patterns reveal root causes faster than guessing.

Related

• Water science — parameters that prevent disease
• Test kit — essential monitoring equipment
• Algae types — water quality issues often show as algae too