Aquarium Fish Diseases

Ich (White Spot Disease) is the most common and deadliest freshwater aquarium disease. The Ichthyophthirius multifiliis parasite creates visible white spots on fish and can wipe out an entire tank if untreated. Treatment requires understanding the parasite's 3-stage life cycle and treating for the full 10-14 day cycle.

Velvet disease creates a fine gold/rust dust appearance on fish skin and is more lethal than ich because it attacks gills aggressively. Treated with copper medication (Cupramine) in a darkened tank. Often harder to detect than ich — use a flashlight at an angle to spot the characteristic shimmer.

Neon Tetra Disease is an incurable parasitic infection that destroys muscle tissue, causing color loss and wasting. No treatment exists — infected fish must be removed immediately to prevent spread. Prevention through quarantine and removing dead fish is the only defense.

HITH/HLLE creates visible pits and erosions on the head and lateral line. Most common in cichlids (oscars, discus, angelfish). Caused by Hexamita parasite exacerbated by poor nutrition and water quality.

Anchor worms are visible crustacean parasites that embed into fish skin. The female worm anchors into the flesh and trails a Y-shaped egg sac. Common in pond fish and newly imported specimens.

Gill flukes are microscopic flatworm parasites that attach to gill tissue, causing inflammation, excess mucus, and breathing difficulty. Can be fatal if untreated as fish suffocate.

Camallanus worms are internal nematode parasites visible as tiny red threads protruding from the fish's vent. Extremely common in guppies, endlers, and other livebearers. Highly contagious — treat entire tank.

Planaria are small flatworms that appear in overfed tanks. While mostly harmless to adult fish, they actively hunt and kill baby shrimp and can overwhelm a shrimp colony. Identified by their distinctive triangular head.

Hydra are tiny freshwater polyps related to jellyfish. They have stinging tentacles that capture and eat baby shrimp, fry, and micro-organisms. Harmless to adult fish but devastating to breeding colonies.

Skin flukes are microscopic flatworms that feed on skin cells and mucus. Unlike gill flukes, they reproduce live (not eggs) so populations can explode rapidly. Fish appear to have a thick slimy coating and scratch constantly.

Black spot disease causes small dark cysts in the skin where larval parasites have encysted. It looks concerning but is rarely harmful to adult fish. Common in wild-caught fish. Spots fade as parasites die off without snail hosts.

Fish lice (Argulus) are flat, disc-shaped crustacean parasites visible to the naked eye. They clamp onto fish skin and feed on blood and tissue fluids. Unlike anchor worms, they can detach and move between hosts.

Internal parasites cause chronic wasting — fish eat but slowly lose weight. White stringy feces is the classic sign. Multiple types of parasites can be involved, often requiring combination treatment.

Fin rot is a bacterial infection that progressively destroys fish fins and tails. It's the most common disease in betta fish and almost always signals poor water quality. Treatment starts with water quality improvement, then salt and antibiotics for moderate to severe cases. Fins can regenerate with proper care.

Dropsy is a critical condition caused by internal organ (kidney) failure, resulting in severe bloating and pinecone-like scale protrusion. It's usually fatal by the time visible symptoms appear. Early detection and aggressive antibiotic treatment offer the best chance, but prevention through excellent husbandry is far more effective.

Columnaris is a highly contagious bacterial infection often mistaken for fungus due to its white, cottony appearance. Unlike ich, LOWER temperature to slow it. Treat with Kanaplex + Furan-2 antibiotic combo. Acute form can kill within 24-72 hours — speed is critical.

Popeye causes one or both eyes to protrude abnormally from the socket. It's usually a symptom of underlying bacterial infection or poor water conditions rather than a disease itself.

Despite its name, mouth fungus is actually bacterial (Flavobacterium columnare). It produces white cottony growths on the mouth that can rapidly erode tissue and spread. Often confused with true fungal infections.

Fish tuberculosis is a chronic, often fatal bacterial disease caused by Mycobacterium marinum. It's one of the few fish diseases that can transmit to humans (zoonotic). Infected fish waste away slowly over weeks to months.

Hemorrhagic septicemia is a severe bacterial blood infection causing red hemorrhages throughout the body. It's one of the most alarming-looking fish diseases — fish appear to be bleeding internally. Rapid treatment essential.

Advanced dropsy treatment guide. When a fish's scales protrude like a pine cone, it indicates severe internal fluid buildup from kidney failure. This is a last-resort treatment protocol using medicated food and Epsom salt.

Aquarium salt is a versatile, gentle remedy for ich, fin rot, velvet, and general stress recovery. This guide covers proper dosing, salt-sensitive species to watch out for, and common mistakes to avoid. Not a permanent additive — use only during treatment periods.

Swim bladder disease is a buoyancy disorder causing fish to float, sink, or swim erratically. Most commonly caused by constipation from overfeeding — treated by fasting 2-3 days then feeding blanched peas. Especially common in fancy goldfish and bettas. Usually resolves within days with proper treatment.

Ammonia poisoning is the #1 killer of aquarium fish. Ammonia (NH3) burns gills and skin, causing suffocation and organ failure. Most common in new, uncycled tanks. Even low levels (0.25 ppm) cause stress; above 1 ppm is often lethal.

Nitrite converts hemoglobin to methemoglobin, turning blood brown and preventing oxygen transport — literally suffocating fish from the inside. The #2 killer after ammonia, most common during the cycling process.

Cloudy eye is usually a symptom of poor water quality rather than a specific disease. The eye develops a milky white film. In most cases, fixing water parameters resolves it within 1-2 weeks.

Complete swim bladder treatment protocol. Most swim bladder issues are caused by constipation or overfeeding and resolve with fasting and peas. Persistent cases may indicate bacterial infection requiring antibiotics.

True fungal infections appear as white cottony growths, usually on damaged tissue. Unlike bacterial columnaris (which looks similar), true fungus has a fuzzy, branching appearance under magnification. Often a secondary infection after injury.