Diseases of aquarium fish. Self-diagnosis and treatment. You will not become a veterinarian, but you can solve or prevent some problems yourself.
Catfish are among the most popular aquarium inhabitants, yet even these hardy fish can fall ill. Aquarium catfish diseases typically stem from two main sources: poor water conditions and external infections introduced through new fish, live food, plants, or snails. In my experience, early symptom recognition and proper treatment are crucial for maintaining fish health and preventing disease spread throughout the tank.
Betta fish (Betta splendens) rank among the most popular aquarium species, but their stunning appearance comes with trade-offs. Selectively bred varieties with elaborate fins have weaker immune systems compared to their wild counterparts. These ornamental finnage makes them particularly vulnerable to infections and physical damage, requiring careful attention to water quality and tank maintenance.
Finally, the aquarium is purchased, plants are planted, and fish are introduced. The joy of a novice aquarist knows no bounds, as their long-cherished dream has come true. But you should never forget that live aquarium fish and other inhabitants of the underwater world are living creatures and are susceptible to various diseases.
The Siamese fighting fish, commonly known as the betta (Betta splendens, Regan, 1910), captivates hobbyists worldwide with its breathtaking color variety and flowing finnage. Native to Southeast Asia — Thailand, Cambodia, and Vietnam — bettas inhabit slow-moving or stagnant freshwater bodies such as rice paddies, drainage ditches, and shallow ponds. Despite their elegant appearance, males are notoriously aggressive toward one another and must always be housed separately.
Chilodonellosis is an invasive disease of aquarium fish caused by the protozoan Chilodonella cyprini, a ciliated infusorian. The parasite has a heart-shaped, elongated, flattened, transparent body covered with cilia. The parasite measures 45-70 μm in length and 38-57 μm in width.
Aquarium fish shock is one of the most serious challenges that every fishkeeper encounters sooner or later. The symptoms vary widely and can mislead even experienced hobbyists. An affected fish may show sudden color fading, abnormally fast or slow gill movement, lethargy, or — on the opposite end — frantic, disoriented swimming as if desperately trying to escape. Eventually, panic gives way to complete stupor: the fish sinks to the bottom, often turns belly-up, and appears dead.
Costiasis (also spelled costiosis) remains one of the most dangerous parasitic infections encountered by aquarium hobbyists. The causative agent — the flagellate Ichthyobodo necator (formerly known as Costia necatrix) — attaches to the skin epithelium and gills, feeding on host cells and mucus. Without timely intervention, the disease leads to mass mortality, particularly among fry and immunocompromised fish.
Columnaris disease is a bacterial infection caused by Flavobacterium columnare (formerly known as Flexibacter columnaris). Nearly every aquarist encounters this pathogen at some point, often mistaking it for a fungal infection. The confusion is understandable—affected areas develop grayish, cotton-like growths that resemble fungus.
Branchiomycosis, commonly known as gill rot, is a dangerous fungal disease affecting the gill apparatus of aquarium fish. The causative agents are two species of fungi from the genus Branchiomyces — B. sanguinis and B. demigrans, which differ in morphological characteristics and developmental features. In my experience, this is one of the most insidious diseases capable of destroying a significant portion of aquarium inhabitants within just a few days.