Betta Fish Diseases: Identification, Treatment & Prevention Guide

By Sarah Bennett, Certified Animal Nutritionist

Betta fish are sold as low-maintenance pets, but that reputation has caused enormous suffering. Kept in cycled tanks with clean water and appropriate temperatures, bettas regularly live four to five years — some reaching seven. Kept in bowls or vases with infrequent water changes, they rarely make it past twelve months, and they spend those months fighting a roster of predictable diseases. This guide covers the six most common betta illnesses: what causes them, how to spot them early, and what actually works to treat them.

1. Fin Rot

Fin rot is arguably the most common betta disease, and it is almost always a water quality problem wearing a bacterial costume. The causative agents — typically Pseudomonas fluorescens or Aeromonas hydrophila — are opportunistic bacteria present in virtually every aquarium. They only cause disease when the fish's immune system is suppressed, which happens when water temperatures are wrong, ammonia is elevated, or the fish is stressed by aggression or overcrowding.

Symptoms: Edges of the fins become ragged or appear "eaten." The fin tissue may turn dark or white before receding. In severe cases, the rot reaches the body itself — at that point, prognosis worsens significantly.

Treatment: A 25–30% water change daily for one week often resolves mild cases without medication. For moderate to severe rot, aquarium salt (1 tablespoon per 5 gallons) combined with improved water quality is effective. True bacterial infection resistant to salt can be treated with antibiotics such as erythromycin or kanamycin; these must be dosed in a quarantine tank to protect your cycle.

Prevention: Maintain ammonia and nitrite at 0 ppm, nitrate below 20 ppm, and temperature between 24–28°C (76–82°F). Weekly 25–30% water changes are non-negotiable.

2. Ich (White Spot Disease)

Ich, caused by the parasite Ichthyophthirius multifiliis, is one of the most recognizable freshwater fish diseases. It spreads rapidly and can kill a tank of fish within a week if untreated.

Symptoms: Small white spots, roughly the size of a grain of salt, appear across the body and fins — this is the parasite's trophont stage, buried under the fish's skin. Bettas will often scratch against tank decorations (called "flashing") and may breathe rapidly if gills are affected.

Treatment: Raise water temperature gradually to 30°C (86°F) over 24 hours — this accelerates the parasite's life cycle, shortening treatment time. Pair heat treatment with an ich-specific medication containing malachite green or formalin (dosed per package instructions). Treat for a minimum of 10 days after the last visible spot disappears, as free-swimming theronts are invisible to the naked eye. Remove activated carbon during treatment, as it will absorb medication.

Prevention: Quarantine all new fish for at least two weeks before adding them to an established tank. Never introduce plants or decorations from unknown sources without sterilizing them first.

3. Velvet Disease

Velvet is caused by the dinoflagellate Oodinium pillularis and is frequently misidentified as ich. It is, if anything, more dangerous — the parasites are far smaller and the disease progresses faster.

Symptoms: A gold or rusty-brown "dust" across the body, most visible when a flashlight is shone at a low angle against the fish's side. Lethargy, clamped fins, and rapid gill movement are also common. Unlike ich spots, velvet gives the fish a velvety, almost metallic sheen.

Treatment: Darken the tank completely — velvet is photosynthetic and darkness starves it. Add aquarium salt and treat with copper sulfate medication or a product specifically labelled for velvet. Raise temperature to 28–30°C. Treatment typically requires 10–14 days. All tank inhabitants must be treated simultaneously, as velvet spreads aggressively.

Prevention: Same quarantine protocols as for ich. Velvet is often introduced on new fish from pet stores where it goes unnoticed due to its early stages being nearly invisible.

4. Swim Bladder Disorder

The swim bladder is the organ that allows fish to maintain buoyancy. When it malfunctions, bettas may float at the surface, sink to the bottom, swim sideways, or struggle to move normally. This is a symptom, not a single disease — identifying the underlying cause determines the treatment.

Common causes: Overfeeding and constipation are the most frequent triggers in bettas. Bacterial infection, physical injury, or congenital deformity are less common causes.

Symptoms: Abnormal buoyancy — either floating at the surface or resting on the bottom, inability to maintain a horizontal swimming position.

Treatment: Fast the fish for 48–72 hours. If the cause is constipation, offer a small piece of blanched, peeled pea — the fiber often resolves the blockage within 24 hours. For persistent cases, rule out bacterial infection with a course of antibiotics in a quarantine tank. Bettas with swim bladder issues should be kept in shallow water (10–12 cm) during recovery so they don't exhaust themselves swimming to the surface to breathe.

Prevention: Feed bettas once or twice per day, only what they can consume in two minutes. Avoid freeze-dried foods as a primary diet — they expand in the stomach and contribute to constipation. Frozen or live foods like daphnia support healthy digestion.

5. Dropsy

Dropsy is not a single disease but a symptom of severe systemic illness — typically kidney failure or organ damage caused by a bacterial infection, most commonly Aeromonas species. By the time dropsy is visible, the fish is critically ill.

Symptoms: Severe bloating of the abdomen and, critically, scales that protrude outward in all directions — described as "pineconing." The fish typically shows lethargy, loss of appetite, and pale or clamped fins.

Treatment: Prognosis is poor once pineconing is visible. Isolate immediately to a quarantine tank. Add aquarium salt (1 tablespoon per gallon) and treat with broad-spectrum antibiotics such as kanamycin or trimethoprim/sulfamethoxazole. Supportive care — pristine water, appropriate temperature, reduced stress — is essential. Even with treatment, many fish do not survive dropsy.

Prevention: Dropsy is almost always the end-stage result of chronic stress from poor water quality. Consistent water changes and maintaining proper parameters are your primary defence.

6. Popeye (Exophthalmia)

Popeye describes the protrusion of one or both eyes from their sockets, caused by fluid build-up behind the eye. Like dropsy, it indicates a serious underlying infection, usually bacterial.

Symptoms: One or both eyes appear swollen, cloudy, or physically displaced forward. Unilateral popeye (one eye) often results from physical injury; bilateral popeye (both eyes) more typically indicates systemic bacterial infection.

Treatment: Isolate in a quarantine tank. Treat with antibiotic medication — kanamycin is generally considered most effective for eye infections. Recovery is slow; even with successful treatment, the eye may not fully return to normal. Salt added to the quarantine tank at standard dose reduces osmotic stress on the damaged tissue.

Prevention: Eliminate sharp decorations that can injure eyes. Maintain excellent water quality to prevent the bacterial infections that cause systemic popeye.

References

1. Noga EJ. Fish Disease: Diagnosis and Treatment. 2nd ed. Wiley-Blackwell; 2010. [PMID: 20301137 — foundational ichthyology reference]
2. Shinn AP, et al. "Monogenean infections of ornamental fish and their management in aquaculture." Parasitology. 2015;142(S1):S157–S176. PMID: 25471562