Constipation / Bloat: causes, symptoms and treatment

Constipation / Bloat — causes, symptoms, diagnosis, intervention and prevention in aquarium fish; mortality without intervention: low.

Overview

Digestive blockage causing swollen abdomen and reduced appetite. Common from feeding inappropriate food (e.g., bloodworms to Mbuna), overfeeding, or low-fiber diet. Dietary/metabolic cause: Dietary indigestion, often complicated by Spironucleus in Mbuna. Reported mortality without intervention: low.

Symptoms

distended belly
reduced or no feces
loss of appetite
lethargy
stringy white feces if Spironucleus complicating
buoyancy issues

Causes

This is a dietary or metabolic disorder rather than an infection, although secondary pathogens may complicate it. The cause is Dietary indigestion, often complicated by Spironucleus in Mbuna. Risk factors include feeding the wrong food type for the species, overfeeding, monotonous diets lacking vitamins or fibre, and feeding raw or thiaminase-rich items. It is not transmissible, but tankmates fed the same diet share the same risk.

Diagnosis

Diagnosis is made from the feeding history together with clinical signs, after ruling out water-quality problems by testing. A monotonous or species-inappropriate diet, overfeeding, or raw thiaminase-rich foods point to a nutritional origin. Where a protozoal complication such as Hexamita or Spironucleus is suspected, a fresh faecal smear or skin scrape under the microscope helps separate the primary dietary problem from a secondary infection.

Treatment

Treatment corrects the diet and supports the affected organ system; recovery is gradual. Fasting, fibre, an Epsom-salt (magnesium sulfate) bath, and a balanced vitamin-rich diet address most cases, with a targeted active substance added only where a secondary infection is confirmed.

Step 1: Isolation

A separate hospital tank is useful when an Epsom-salt bath or medicated food is needed, but the diet correction applies to the whole tank. If you do isolate the fish, match temperature and pH to the display tank, keep the bottom bare for easy siphoning, and acclimate slowly to avoid adding stress to an already weakened animal.

Step 2: Intervention

Fast + Epsom salt + fiber. Stop feeding 2-3 days, then offer blanched deshelled pea or daphnia. Add Epsom salt 1 tbsp per 5 gal as laxative. Metro if Mbuna bloat suspected. (duration: 3-5 days)

Step 3: Recovery

Recovery is gradual and measured in weeks to months. Keep the corrected, varied, vitamin-rich diet in place permanently, maintain regular water changes, and watch body condition and appetite as the markers of progress. Reintroduce the fish to the display only once feeding and buoyancy or condition are reliably normal.

Prevention

feed species-appropriate diet
no animal protein for herbivorous Mbuna
add fiber (peas, daphnia, spirulina)
avoid overfeeding
fasting 1 day weekly