Bloat and Internal Parasites in Fish: Signs and Treatment
Bloat vs dropsy
Bloat is a swollen belly that may come from constipation, diet, internal parasites or bacterial infection. Unlike dropsy, the scales usually lie flat. If scales stick out, treat it as dropsy.
Signs of internal parasites
- White, stringy or clear waste
- Thin body with a hollow belly despite eating
- Loss of color and lethargy
- Pitting on the head or lateral line, common in cichlids and discus
Common causes of bloat
- Overfeeding dry, expanding foods
- Constipation from a low-fiber diet
- Flagellate parasites such as Hexamita and Spironucleus
- Bacterial infection in the gut or body cavity
What to try first
- Fast the fish for a day or two, then offer blanched, deshelled peas or other fiber-rich food.
- Keep water clean and stable.
- If waste stays stringy or the fish loses weight, suspect parasites.
Where metronidazole fits
Metronidazole is an antiprotozoal and antibacterial for anaerobes. It is widely used by aquarists for internal flagellates. Fish that refuse food can be treated through the water in a hospital tank, following the directions on the label.
When bacteria are involved
If bloat comes with red patches, hemorrhaging or fast deterioration, a bacterial infection may be present and a systemic antibiotic such as doxycycline may be needed. Our Internal Parasite and Bloat Pack combines both approaches.
Frequently asked questions
What causes bloat in fish?
Overfeeding, constipation, internal parasites and bacterial infections are the most common causes. Diet and water quality are the first things to review.
How do I know if my fish has internal parasites?
White stringy waste, weight loss while still eating, pale color and, in some species, head pitting are typical signs.
Can metronidazole be used for bloat?
It is commonly used when bloat is linked to internal protozoa or anaerobic bacteria. It will not help if the cause is constipation or a different pathogen.