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systemic internal

Intestinal prolapse (rectal prolapse)

A section of intestine protruding from the vent, appearing as a pink, red, or brownish tube-like structure. Often confused with Camallanus worms, but prolapsed tissue is wider, irregular, and does not move independently. Usually caused by severe constipation, straining, internal parasites, or bacterial infection of the gut.

High prioritypattern match not diagnosis1 source note

Do first

  • Distinguish prolapse from Camallanus worms: prolapsed tissue is a wider, soft, pinkish-red tube; Camallanus worms are thin, thread-like, and reddish-brown.
  • Do not attempt to push the prolapsed tissue back in manually without guidance.
  • Move the fish to a hospital tank with clean water.
  • Apply a gentle osmotic bath using diluted Epsom salt solution (1 tsp per gallon) for 10 to 15 minutes to help reduce swelling and encourage retraction.
  • Do not feed the fish during assessment and initial treatment.

Escalate if

  • Tissue is dark, black, or clearly necrotic. Humane euthanasia should be considered.
  • Prolapse does not resolve with 48 hours of Epsom salt treatment.
  • Fish is in severe distress, not eating, and declining rapidly.
  • Prolapse recurs repeatedly after resolution. Investigate internal parasites or bacterial gut disease.

Water clues

These readings can push this pattern higher or lower in the triage result.

ammonia above zero+2

Poor water quality can worsen secondary infection of exposed tissue. Correct water quality immediately.

Care protocol

Follow only the steps that fit your species, tank inhabitants, and medication label.

Prolapse vs. worms: identification

  1. View from the side and from behind under bright light.
  2. Prolapsed intestine: wide (1 to 5 mm), pink to red-brown, soft, irregular surface, usually a single rounded mass.
  3. Camallanus worms: thin (less than 1 mm), thread-like, can be multiple, may move or retract slowly.
  4. Prolapse often occurs alongside straining posture: the fish arches the body or sits with the tail lowered.
  5. If uncertain, do not treat as worms first. Anthelmintics will not resolve a prolapse.
Cautions
  • Prolapsed tissue that has been exposed for more than a few hours will begin to dry, swell, and necrotize.
  • Do not confuse with normal spawning tube extrusion in females, which is shorter and firmer.

Treatment protocol

  1. Mild prolapse (tissue still pink, recently appeared): gentle Epsom salt baths twice daily (1 tsp per gallon, 10 to 15 minutes). Many mild cases retract within 24 to 48 hours.
  2. If the tissue retracts, fast the fish for 3 days, then offer easily digestible food in small amounts.
  3. If the tissue is swollen, necrotic (dark or black), or has not retracted within 48 hours: humane euthanasia is often the kindest outcome.
  4. For fish with a suspected underlying cause (internal parasites, bacterial gut infection): treat with appropriate medication after the prolapse is resolved or concurrent with Epsom salt baths.
  5. If the prolapse recurs: investigate diet, internal parasites, and chronic straining.
Cautions
  • Do not attempt surgical reduction without veterinary guidance.
  • If the exposed tissue is necrotic, attempts at reduction can introduce systemic infection.
  • Prolapse in a fish that is also very thin or wasting suggests a serious underlying condition.

Source notes

References and context notes used for this triage entry.

Rectal prolapse in fish: general veterinary referenceMerck Veterinary Manual general fish disease section. Consult an aquatic veterinarian for surgical or advanced cases.
Run Symptom CheckerCompare this pattern against water readings, affected count, and recent tank context.Ask AdvisorUse TankFlare Advisor to review this against your saved tank and recent logs.

Related patterns

Similar symptoms or risk factors worth comparing before treatment.

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UrgentDropsy (pinecone scales / severe bloating)

Severe abdominal bloating with scales raised outward like a pinecone, indicating fluid accumulation in the body cavity. Dropsy is a symptom complex not a single disease caused by internal bacterial infection, organ failure, or severe parasitic infestation. Prognosis is often poor by the time scales are raised.

MonitorBloat and constipation (digestive)

Mild-to-moderate abdominal swelling without raised scales, often linked to overfeeding, a diet too low in fiber, or dry food that expands after eating. Very common in bettas, goldfish, and other heavy eaters. Distinguished from dropsy by the absence of pinecone scales and by a more localized, often asymmetric swelling.

Medium priorityInternal parasites / wasting disease

Progressive weight loss and sunken belly despite normal or increased appetite, often with abnormal feces (stringy, white, or mucus-laden). Caused by various internal parasites including Hexamita, Spironucleus, Capillaria, or other nematodes. Common in wild-caught fish and recently imported specimens.