Goldfish are prone to a variety of freshwater diseases.

As a goldfish owner, it’s important to be aware of certain conditions and illnesses that may affect them.

1. Poor Water Quality

While not a disease itself, poor water quality is the leading cause of illness in goldfish. Goldfish are messy and produce a lot of waste, which can quickly foul the water. Inadequate environments, such as outdated bowls or overcrowded tanks—lead to chronic stress due to poor water conditions.

To keep your goldfish healthy, it’s crucial to provide them with enough space. For comet and other long-bodied varieties, start with at least 20 gallons per fish, and plan for 50 to 75 gallons per fish as they mature, as goldfish can grow to 14 to 16 inches in length. Avoid small bowls, as no fish deserves to live in filthy water. Goldfish require filtered tanks but do not need heaters.

2. Parasites

Purchasing a fish from a pet store is the most common way goldfish can contract parasites. Pet stores often mix fish from various sources and environments, which increases the risk of parasites spreading through the water and on equipment.

Signs of parasites in goldfish include missing scales, abnormal behavior (like flashing or bruising), lethargy, or sudden death. Common goldfish parasites include:

Ichthyophthirius multifiliis (White Spot Disease)

Trichodina

Monogenean trematodes (Flukes)

Ichthyobodo (Costia)

Lernaea spp. (Anchor Worms)

Argulus spp. (Fish Lice)

Chilodonella

The best defense against parasites is a strict quarantine procedure for new fish. Treatment varies depending on the specific parasite, so it’s essential to get a proper diagnosis from an aquatic veterinarian. Avoid self-diagnosing and using over-the-counter medications, as this can harm your fish and worsen the problem.

3. Neurofibromas

Neurofibromas, or benign tumors, are commonly seen in comet goldfish, particularly those kept outdoors. These growths develop from neural tissue deep within the skin layers and are difficult to treat. Neurofibromas often form a stalk and may fall off, only to grow back. Some goldfish may have one or two localized lumps, while others may have multiple growths scattered across their bodies.

4. Buoyancy Disorders

Goldfish can experience both positive and negative buoyancy disorders, which affect their ability to swim properly.

Positive buoyancy disorders are often caused by the goldfish swallowing excess air while feeding. This can lead to air trapped in the swim bladder or gastrointestinal tract.

Negative buoyancy disorders are typically caused by stress or poor diet, causing the fish to lack the energy or inclination to swim. Once the stressor is removed and a proper diet is introduced, the fish should return to normal behavior.

5. Polycystic Kidney Disease

Goldfish are susceptible to polycystic kidney disease (PKD), a condition where cysts form in the kidneys, causing malfunction and tissue damage. The exact cause of PKD is unknown, and unfortunately, there is no known cure. Once the kidneys are damaged, they do not recover.

6. Cloudy Eyes and Popeye

Cloudy eyes in goldfish are often a result of poor water quality, trauma, or secondary infections. Some fancy goldfish varieties, with eyes that protrude more than usual, are particularly prone to eye injuries.

7. Red Streaks on Skin and Fins

Red streaks on the skin or fins are typically signs of stress or poor water quality. If you notice these on your goldfish, check the water quality immediately, as improving the conditions may resolve the issue.