Fish health
Diseases, prevention, quarantine, an aquarist's medicine cabinet.
Deep-diveAquarium fish diseases — diagnostic algorithm and 8 key conditions
How to spot illness by behaviour and look, a four-step diagnostic protocol and treatment outlines for the 8 most common diagnoses: ich, velvet, columnaris, dropsy, swim bladder, saprolegnia, internal parasites, gill flukes.
Deep-diveVelvet disease (oodinium) in aquarium fish — symptoms, treatment, prognosis
Golden-grey 'dusty' coating on the skin, fast breathing, loss of appetite. A dangerous dinoflagellate parasite — treated with darkness, copper and heat. Without therapy, mortality in 3–7 days.
Deep-diveColumnaris in aquarium fish — telling it from fungus and treating it
A bacterial disease often mistaken for fungus. Greyish-white cotton-like patches on head and fins; the aggressive strain can kill in 24 hours. Treatment — antibiotics, lower temperature, salt.
Deep-diveDropsy (pinecone) in fish — what it is, causes and odds of saving them
Raised scales, bloated belly, bulging eyes — not a disease in itself but a symptom of severe internal infection. Prognosis is grim: fewer than half survive even with correct treatment.
Deep-diveSwim bladder disorder — why your fish is swimming on its side
The fish floats belly-up, lies on its side, can't hold its position in the water. Causes range from simple constipation to bacterial infection and congenital deformity. A clear diagnostic and treatment plan.
Deep-diveSaprolegnia (fungus) on fish and eggs — treatment and root causes
White cotton-like tufts on wounds, fins or eggs. The fungus is an opportunist — it only attacks already-stressed fish. The key to treatment is removing the underlying cause (injury, bad water, stress); the fungus itself comes off easily with methylene blue.
Deep-diveInternal parasites in fish: Camallanus and Hexamita — diagnosis and treatment
Red worms protruding from the vent (Camallanus) or white stringy faeces and 'hole-in-the-head' in discus (Hexamita) — two different parasites needing different drugs: levamisole and metronidazole. Detailed treatment protocol.
Deep-diveGill and skin flukes (Dactylogyrus, Gyrodactylus) — diagnosis and treatment
Microscopic flatworms on gills and skin. Symptoms — fast breathing, flashing, mucus clouding. Often present latently and flare up under stress. Treatment — praziquantel.
Deep-diveFish mycobacteriosis (fish TB) — diagnosis, incurability and risk to humans
A chronic bacterial infection (Mycobacterium marinum, M. fortuitum) that's essentially untreatable. Progressive wasting, spinal curvature, ulcers. A dangerous zoonosis: humans get infected through skin wounds.
Deep-diveFish hanging at the surface: 5 diagnoses
Almost always a red flag — except for a few species for which it's normal.
Deep-diveQuarantining new fish: a 4-week protocol
The most underrated routine in the hobby — it stops new fish from bringing disease into a mature tank.
Deep-diveIch: salt and temperature treatment
White spot is the most common disease. Caught early, it's treatable without harsh chemistry.
Deep-diveFin rot: identification and treatment
A bacterial infection of the fins. Early-stage fin rot clears with water changes; later stages need antibiotics.
GuideHospital tank: setup and use
When you can't dose the main tank with meds, you need a separate one. How to set it up, keep it ready, and not kill the patient.