Knowledge Centre · Fish health and behaviour

Swim bladder problems in aquarium fish: causes and what to do

A fish that's floating helplessly, sinking to the bottom, swimming sideways, or flipped upside down is showing a buoyancy problem usually linked to its swim bladder — the internal, gas-filled organ that normally lets a fish hold its position in the water without constant effort. "Swim bladder disorder" describes this symptom rather than one single disease: several different underlying causes can produce it, including diet, water quality, infection, injury and body conformation[1]. This guide explains what to check and try first — it isn't a diagnosis for your specific fish.

At a glance

What it usually means

A buoyancy problem — most often diet-related in fancy goldfish and similar species, but with several possible causes.

Try first

A short fast plus a small amount of skinned pea if constipation seems likely, alongside checking water quality.

What this page won't do

Recommend surgery or invasive treatment — those are clinical decisions for a vet, not a DIY step.

Understanding swim bladder problems

The swim bladder is a gas-filled internal organ that allows a fish to control its buoyancy and hold a chosen depth without constantly expending energy swimming. When it isn't working correctly, a fish may float at the surface unable to submerge, sink to the bottom unable to rise, swim on its side, or flip upside down[2].

It's worth thinking of "swim bladder disorder" as a description of the symptom rather than a single diagnosis. A veterinary review of the condition in koi identifies poor water quality, infectious agents, poor nutrition, tumours, injuries and genetic factors as all being proposed causes[1] — which is why working through the possibilities methodically matters more than assuming one universal cause or fix.

Likely causes

  • Diet and constipation. Overfeeding, or feeding dry floating pellets that expand and cause a fish to gulp air while feeding, is widely reported as a common trigger[3], particularly in fancy goldfish varieties with rounded, compressed body shapes.
  • Water-quality stress. Poor water quality is specifically identified as a contributing factor[1], and stressed fish are generally more susceptible to a range of problems. See our ammonia and nitrite guides.
  • Infection. Bacterial or other infectious agents affecting the swim bladder or surrounding organs are a documented cause, not just a diet issue.
  • Physical injury. A fall, collision, or rough handling can damage the swim bladder directly.
  • Genetic and conformation factors. Selectively bred, rounder-bodied varieties (many fancy goldfish, some bettas) are more prone to this issue as a consequence of their body shape, independent of anything the keeper has done.
  • Tumours, rarely. Listed as a possible but less common cause[1], worth being aware of without treating it as the most likely explanation.

Immediate actions

Rule out the common causes

  1. Test your water quality

    Poor water quality is a recognised contributing factor, so this is worth checking regardless of the suspected cause.

  2. Consider a short fast

    Withholding food for 24–48 hours is a commonly reported first step when constipation is suspected, giving the digestive system a chance to clear.

  3. Offer a small amount of skinned, cooked pea afterward

    Some keepers use this as a mild, fibre-based supportive step for suspected constipation — it's a widely reported practice, not a guaranteed cure.

Support the fish

  1. Reduce water flow around the affected fish temporarily

    A fish struggling with buoyancy can find strong current exhausting to work against.

  2. Minimise handling

    Avoid netting or moving the fish more than necessary while it's affected.

What to check next

  • Is the fish otherwise behaving normally — still eating, alert, and not showing other signs — aside from the buoyancy issue?
  • Has feeding recently involved dry, floating pellets fed without soaking, or noticeable overfeeding?
  • Does the fish's body look bloated, or unusually thin, which can point toward different underlying causes?
  • Is only one fish affected, or several? A single fish points more toward an individual issue (diet, injury, conformation); several at once points more toward a tank-wide water-quality or infectious cause.
  • Is there any visible swelling, redness or other sign alongside the buoyancy problem?

When it may be more serious

Seek specialist help if: buoyancy problems persist for more than a few days despite fasting and confirmed good water quality, the fish shows visible swelling, redness, or other signs of infection, it can't feed or reach the surface for air where that matters for the species, or several fish are affected at once. A vet may consider options such as aspirating excess gas from the swim bladder, which should only ever be performed by a qualified professional, not attempted at home[2]. This guide provides general informational guidance, not a diagnosis or treatment plan for your specific animal. Contact an aquatic veterinarian or a suitably experienced aquatic-health specialist for persistent or severe cases.

Common mistakes

  • Assuming every case is constipation and skipping a water-quality check.
  • Feeding dry, floating pellets without soaking them first for species prone to this issue.
  • Attempting to manually treat or aspirate the swim bladder at home — this is a clinical procedure for a vet, not a DIY fix.
  • Ignoring a persistent case in the hope it resolves on its own.
  • Keeping a severely affected fish in strong current, where it struggles further rather than recovering.

Prevention

  • Soak dry, floating pellets briefly before feeding, particularly for goldfish and other species prone to this issue.
  • Avoid overfeeding, and feed smaller amounts more than once a day rather than one large feeding.
  • Offer a varied diet with appropriate fibre — some keepers include skinned peas occasionally for this reason.
  • Maintain stable, good water quality, since stress increases susceptibility to a range of problems.
  • Handle fish gently and minimise unnecessary netting or transport.
Good to know: this guide provides general informational aquarium-care guidance. It is not a veterinary diagnosis or treatment plan and does not replace specialist or veterinary advice for serious livestock health issues.

Frequently asked questions

Is swim bladder disease contagious?

Usually not directly. Swim bladder problems are most often an individual issue linked to diet, water quality, injury or conformation rather than something that spreads fish-to-fish. An exception is when an underlying infection is the cause, in which case the same conditions that led to it could plausibly affect other fish too.

Will feeding peas cure swim bladder problems?

Not guaranteed. Offering a small amount of skinned pea, and briefly fasting the fish, is a commonly reported supportive step when constipation is suspected as the cause, but it isn't a universal cure. If buoyancy problems persist despite this, or the cause isn't diet-related, it won't help and other causes need ruling out.

Can swim bladder problems be cured?

It depends on the cause. Diet-related or mild, temporary cases often improve with fasting and dietary changes. Cases caused by infection, injury, or genetic conformation are more variable, and some fish live indefinitely with ongoing mild buoyancy issues managed through diet and environment rather than fully resolved.

Is swim bladder disorder more common in certain species?

Yes. It's particularly commonly reported in fancy goldfish varieties with rounded, compressed body shapes, and in bettas, likely related to body conformation from selective breeding as well as diet and feeding style.

How AquaPulse Water Check can help

Buoyancy problems usually have a short history behind them — a diet change, a temperature swing, water quality that had already started slipping — and that history matters more than today's single reading does. The sequence is hard to reconstruct after the fact if nothing was written down. Logging your readings and diet changes together in AquaPulse as you go means that sequence already exists when you need to look back at it, instead of piecing it together from memory under pressure.

Water Check works from the information you enter — it can't assess buoyancy or body condition, and isn't a substitute for testing your water with a reliable kit, or for professional or veterinary advice when a fish is seriously or persistently affected. Get AquaPulse on the App Store or Google Play to try it, or see the Water Check feature page for more detail.

Sources and editorial information

Published
19 July 2026
Last reviewed
19 July 2026
Written and maintained by
AquaPulse (Valeon Labs Ltd)

This guide is written and maintained by the AquaPulse team at Valeon Labs Ltd. It draws on a peer-reviewed veterinary journal article and general reference sources rather than a single author's personal experience, and we paraphrase and link to those sources rather than reproducing their wording. We'll update this page if the sources it's based on change, or if we find something we've got wrong.

Good to know: This guide provides general informational guidance only. It is not a veterinary service and does not replace specialist or aquatic health advice for serious livestock health issues.

Aquarium Emergency Diagnosis

Ranks the likely causes for a symptom like this and what to check first — not a diagnosis, but a sensible starting point.

Why has my fish stopped eating?

Diet and digestion are linked to both appetite and swim bladder issues.

Why is my fish lying on the bottom?

Read this instead if the fish is resting normally, without any loss of buoyancy control.

Ammonia in aquariums: what it means and what to do

Poor water quality is a recognised contributing factor — test this first.

Nitrite in aquariums: what it means and what to do

Test alongside ammonia when a fish is affected.

Water Check in the AquaPulse app

Record your readings and get a plain-language explanation of what they may mean.
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