Goldfish Diseases With Pictures: Symptoms & Treatment

Goldfish diseases can cause white spots, damaged fins, swelling, or changes in swimming and appetite. Early signs may be less obvious, such as hiding, rubbing against decorations, or refusing food. Poor water quality can cause similar symptoms and make infections harder to fight, so checking the water is an important first step.

This guide covers common goldfish diseases and health problems, with pictures, signs to look for, and an overview of treatment. Each section links to a detailed guide if you need more help identifying or treating the problem.

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What Causes Goldfish Diseases?

Infections, parasites, and poor tank conditions can make goldfish ill. Stress and poor nutrition can also weaken their resistance to disease.

• Poor water quality: Ammonia damages the gills; nitrite reduces the blood’s ability to carry oxygen.
• Sudden temperature changes: Rapid shifts stress fish and can weaken their immune response.
• Overcrowding: Too many fish increase waste, oxygen demand, and the spread of infections.
• New additions: Fish, plants, and shared equipment can introduce pathogens. Quarantine new fish and clean equipment between tanks.
• Overfeeding and poor nutrition: Excess food pollutes the water, while an unbalanced diet weakens disease resistance.
• Dead fish: Decomposition worsens water quality. Remove dead fish promptly and investigate the cause.

Goldfish Disease Chart

Compare your goldfish’s signs with the chart below, then follow the relevant link for more detail. Similar symptoms can have different causes, so check water quality before choosing treatment.

Bacterial Goldfish Diseases

These are caused by bacteria present in almost every tank and pond at low levels, only becoming a problem once a fish’s immune system is weakened.

Goldfish Fin Rot

Fin rot is a bacterial infection that causes fin edges to fray, discolor, and gradually break down. Unlike a simple tear, the damage continues spreading, sometimes with redness along the affected edges.

Poor water quality, stress, and fin injuries can allow the infection to develop. Mild cases may improve with consistently clean water and removal of the underlying stressor. If tissue loss continues or the infection is advanced, an appropriate antibacterial treatment may be needed.

See our goldfish fin rot guide for the stages, treatment steps, and signs of recovery.

Goldfish Mouth Rot (Columnaris)

Mouth rot is a bacterial infection often associated with columnaris. It can cause white or gray patches around the mouth, redness, and eroding tissue that makes eating difficult. Sometimes called “mouth fungus,” it can resemble a fungal infection but needs different treatment.

Some cases progress quickly, especially in warmer water. Check and correct water quality, keep the temperature stable, and use an appropriate antibacterial treatment. Avoid raising the temperature or combining medicines without checking their instructions.

See our goldfish mouth rot guide for help distinguishing it from fungus and following the treatment steps.

Goldfish Red Pest Disease (Hemorrhagic Septicemia)

“Red pest” is a hobby term for bacterial illness associated with blood-red streaks, patches, or sores on the skin and fins. Severe infections can affect internal organs. However, red marks alone do not confirm septicemia; ammonia exposure, injuries, and parasites can cause similar signs.

Check water quality first and correct any problems. If a bacterial infection is strongly suspected, an appropriate antibiotic may be needed; medicated food can deliver treatment internally when the fish is still eating. Monitor tank mates too, because they share the same water and may have been exposed to the bacteria.

See our goldfish red pest disease guide for treatment steps and how to distinguish it from ammonia-related damage.

Fungal Goldfish Diseases

Fungal growth often develops on skin or fins already damaged by injury, parasites, or another infection.

Goldfish Fungal Infection

White or gray, fluffy growth on the body or fins can indicate a fungal infection. Common cases involve water molds such as Saprolegnia. Bacterial mouth rot can look similar, so cotton-like patches around the mouth should not automatically be treated as fungus.

Treatment involves a suitable antifungal medication, clean water, and addressing the original injury or illness. White marks on an Oranda’s wen alone do not confirm fungus—or harmless growth. Spreading fuzz, redness, or tissue damage needs closer investigation, even if the fish is still eating.

See our goldfish fungal infection guide for identification, treatment steps, and how it differs from bacterial mouth rot.

External Parasitic Goldfish Diseases

These parasites affect the skin, fins, or gills. Some are microscopic, while others, such as anchor worms and fish lice, are visible without magnification.

Goldfish Ich (White Spot Disease)

Ich is a contagious parasitic infection that typically causes tiny, salt-like white spots on the skin and fins. Affected fish may rub against decorations, clamp their fins, or breathe rapidly. After feeding on the fish, the parasite drops off, forms a cyst on aquarium surfaces, and multiplies before releasing new parasites into the water.

Treat the affected aquarium, not just fish with visible spots, using a suitable ich medication. Maintain good aeration and complete the product’s treatment schedule even if the spots disappear, because parasites can remain in the tank. Temperature affects the life cycle, but raising it is not a substitute for treatment.

See our goldfish ich guide for treatment steps, lookalike conditions, and when temperature adjustments may help.

Goldfish Velvet Disease

Velvet is a parasitic infection that can give the skin a fine gold or rust-colored coating. Fish may also rub against objects, clamp their fins, or breathe rapidly. A flashlight can make the coating easier to see, but it cannot confirm velvet because natural metallic coloring can look similar.

Treat the affected aquarium with a medication labeled for freshwater velvet, following its full dosing schedule. Maintain good aeration; dimming the lights may support treatment but will not clear the infection alone. Copper-based products require particular care with dosing and are unsuitable for tanks containing shrimp or snails.

See our goldfish velvet disease guide for identification and treatment steps.

Goldfish Gill Flukes

Gill flukes are tiny parasitic flatworms that attach to the gills, causing irritation and damage that can make breathing difficult. Signs include rapid gill movement, gasping, and rubbing against objects. Poor water quality and low oxygen can cause similar behavior, so check these first; identifying flukes usually requires microscopic examination.

Praziquantel is commonly used to treat gill flukes. Egg-laying flukes can leave eggs that survive the initial treatment, so repeat doses may be needed according to the product’s instructions. Treat the affected aquarium and maintain good aeration.

See our goldfish gill flukes guide for treatment steps and how gill flukes differ from skin flukes.

Goldfish Anchor Worm

Anchor worm is a crustacean parasite, not a true worm. Adult females embed themselves in the fish’s tissue, leaving a visible, thread-like body protruding from the skin. The attachment site may become red, swollen, or ulcerated, and the fish may rub against objects.

Attached adults may need careful removal by an experienced keeper or aquatic veterinarian, since pulling them out can damage tissue or leave part embedded. The aquarium also needs treatment with a product intended for anchor worms to target developing parasites. Removing the visible adults alone will not clear the infestation.

See our goldfish anchor worm guide for removal precautions, treatment options, and follow-up care.

Goldfish Lice

Fish lice (Argulus) are small crustacean parasites that appear as flat, greenish or translucent discs attached to the skin or fins. Their feeding damages the skin, causing irritation, rubbing, and small red wounds that may develop secondary infections.

Visible lice can be carefully removed by someone experienced, but removal alone will not eliminate the infestation. Treat the affected aquarium or pond with a product labeled for fish lice and follow its repeat-treatment schedule, because eggs on tank surfaces may hatch later. Keep the water clean while wounds heal.

See our goldfish lice guide for removal precautions, medication options, and follow-up treatment.

Internal Parasitic Goldfish Diseases

Internal parasites can affect the digestive tract and other organs. They often remain unseen, with signs such as weight loss or declining condition prompting investigation.

Goldfish Camallanus Worms (Red Worms)

Camallanus are intestinal roundworms. Adult females may protrude from the fish’s vent as thin, red threads, although infected fish do not always show visible worms. Heavy infections can damage the intestine and cause weight loss and weakness.

Levamisole can be used through the water, while fenbendazole is an option in medicated food. Both target intestinal worms, including those not visible at the vent. Treat all exposed fish, follow the medication’s repeat-treatment schedule, and vacuum the substrate to reduce reinfection. Never pull protruding worms out with tweezers, as this can injure the fish.

See our goldfish Camallanus worms guide for medication options, repeat dosing, and tank cleaning.

Goldfish Hexamita

Hexamita and related intestinal flagellates can be associated with weight loss, reduced appetite, and pale, stringy feces. These signs do not confirm infection: stringy feces can also occur when a fish has not eaten. Microscopic examination can help identify the cause.

Metronidazole is used to treat diagnosed intestinal flagellate infections, often through medicated food when the fish is eating. Correct water-quality and nutrition problems alongside treatment. Hexamita should not be treated as another name for hole-in-the-head disease; head pits can have other causes.

See our goldfish Hexamita guide for diagnosis, treatment options, and its debated connection to hole-in-the-head disease.

Other Goldfish Health Problems

Dropsy, popeye, swim bladder problems, and a bent spine are not always caused by infection. They can also involve injury, organ disease, nutrition, or body structure, so treatment depends on the underlying cause.

Goldfish Dropsy

Dropsy describes fluid buildup that causes body swelling and, in advanced cases, raised scales resembling a pinecone. It is a sign of an underlying problem, such as infection, organ disease, or toxin exposure, rather than a disease with one specific cause.

Check water quality promptly and provide clean, well-aerated water while investigating the cause. Antibiotics may help when a bacterial infection is responsible, but they will not treat every case. Severe swelling and pineconing carry a poor outlook and need prompt attention from an aquatic veterinarian.

See our goldfish dropsy guide for supportive care, treatment options, and recovery expectations.

Goldfish Popeye

Popeye describes abnormal swelling of one or both eyes. One swollen eye may follow an injury, while swelling in both eyes can suggest a broader problem, such as an internal infection or fluid imbalance. The number of affected eyes offers a clue but does not confirm the cause.

Check water quality and remove sources of injury, including sharp decorations or aggressive tank mates. Treatment depends on the cause; antibiotics are not automatically needed just because an eye is swollen. Epsom salt is sometimes used as supportive care, but it does not treat an underlying infection or injury.

See our goldfish popeye guide for possible causes, treatment options, and signs of recovery.

Goldfish Swim Bladder Disorder

Swim bladder problems can make a goldfish float uncontrollably, sink, or struggle to stay upright. Fancy goldfish are particularly prone to buoyancy problems because of their body shape. Feeding, internal disease, and structural abnormalities can all contribute, so overfeeding should not automatically be assumed.

Check water quality and review feeding first. Smaller portions and sinking food may help feeding-related problems, but peas are not a cure for every case. Persistent buoyancy difficulties, especially with swelling, appetite loss, or worsening weakness, need further investigation.

See our goldfish swim bladder disease guide for possible causes, feeding adjustments, and treatment options.

Goldfish Bent Spine (Scoliosis)

A bent spine can appear as a C-shaped curve, where the backbone bends to one side, or an S-shaped curve, where it bends in two opposing directions. Possible causes include developmental abnormalities, injury, nutritional deficiencies, and some diseases.

Provide fresh, nutritionally complete goldfish food, but do not expect diet changes to straighten an established deformity. A new or worsening curve, especially with weight loss or difficulty swimming, needs investigation. For permanent cases, care focuses on helping the fish swim and reach food comfortably.

See our goldfish bent spine guide for possible causes and care options.

What to Check Before Using Medication for Goldfish Diseases

Different problems can cause similar symptoms, so check these before choosing treatment:

• Water quality: Test ammonia, nitrite, nitrate, pH, and temperature. Correct any problems first.
• Other signs: Look for spots, sores, damaged fins, swelling, or rapid breathing to help narrow down the cause.
• Medicine compatibility: Combine products only when their instructions explicitly allow it or an aquatic veterinarian recommends it.
• Treatment instructions: Follow the specified dose, treatment length, and water-change schedule.

Methylene blue is not a universal first treatment. Choose medication for the likely cause rather than adding several products to cover every possibility.

How to Prevent Goldfish Illnesses

Good care reduces disease risk, though it cannot prevent every illness.

• Maintain water quality: Test regularly, keep ammonia and nitrite at 0 ppm, and perform partial water changes using dechlorinated water.
• Quarantine new fish: Observe them separately before introduction. Inspect new plants and clean equipment before sharing it between tanks.
• Avoid overcrowding and bullying: Provide enough space, effective filtration, and compatible tank mates.
• Feed a balanced diet: Use fresh, nutritionally complete goldfish food and remove uneaten leftovers.
• Maintain the filter: Rinse clogged media gently in removed tank water or dechlorinated water. Avoid replacing all biological media at once.
• Keep conditions stable: Avoid sudden temperature changes and maintain good aeration.
• Observe your fish daily: Investigate changes in breathing, appetite, swimming, or appearance. Remove dead fish promptly and check the remaining fish.

Frequently Asked Questions

How do I know if my goldfish is sick?

Changes in appetite, breathing, swimming, or activity can signal a problem. Look for clamped fins, spots, sores, or swelling alongside these changes. Test the water first, because poor conditions can cause similar signs.

Can goldfish diseases spread to other fish?

Some infections and parasites spread through shared water or contaminated equipment. Other problems, such as an injury or a developmental deformity, are not contagious. For conditions such as dropsy or popeye, the risk depends on the underlying cause.

Should I separate a sick goldfish?

A hospital tank can help if the fish is being bullied, cannot reach food, or needs medication unsuitable for its tank mates. Provide clean, appropriately matched water, aeration, and established biological filtration where possible. For ich or velvet, the main aquarium may still need treatment after the fish is moved.

Are goldfish diseases dangerous to humans?

Fish and aquarium water can carry germs that infect people, even when the fish look healthy. Wash your hands after tank maintenance and wear waterproof gloves, especially if you have cuts or wounds. See the CDC’s aquarium hygiene advice.

Why is my goldfish not eating?

Poor water quality, stress, unsuitable food, and illness can all reduce appetite. Check whether other fish are affected and look for changes in breathing, swimming, or appearance. Our goldfish not eating guide covers the possible causes.

Why is my goldfish sitting at the bottom?

Brief resting can be normal, but persistent bottom sitting with clamped fins, rapid breathing, or appetite loss needs investigation. Water problems, illness, or difficulty staying buoyant may be involved. See our goldfish staying at the bottom guide.

Why is my goldfish staying at the top of the tank?

Repeated surface gasping can indicate low oxygen, poor water quality, or damaged gills. Increase surface agitation, check that the filter is working, and test the water promptly. Our goldfish staying at the top guide explains what to check next.

Related Goldfish Symptom Guides:

• Goldfish Swimming Erratically
• Goldfish Swimming Upside Down
• Goldfish Turning Black
• Goldfish Turning White