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Swim bladder disorders

By the koi.wiki editorial team · Updated

Key facts: Swim bladder disorders (also called swim bladder disease or buoyancy disorder) are conditions in which a koi loses the ability to control its depth in the water, floating, sinking, or swimming abnormally due to a malfunction of the gas-filled swim bladder organ.[1][2]
The swim bladder is an internal, gas-filled organ that allows bony fish, including koi, to hold a chosen depth without expending energy swimming.[3][4] In koi it is described as a two-chambered organ that controls buoyancy, letting the fish float at different depths without effort.[5] When this system is disrupted, a koi may float nose-down and tail-up, sit at the surface, or sink and struggle to rise, a condition generally termed swim bladder disease or “flipover” in aquarium fish.[1]According to the koi dealer Kodama Koi Farm, swim bladder disease covers two distinct buoyancy disorders — positive and negative — each with its own likely causes and management approach.[2]

Anatomy and function of the swim bladder

The swim bladder sits dorsally within the body cavity and consists of gas-filled chambers whose expansion or contraction adjusts the fish's buoyancy.[4][3] In koi anatomy, it is described as a two-chambered, gas-filled organ that allows the fish to float at a given depth without using energy to swim.[5] Because the organ is positioned above the center of mass, its expansion helps stabilize the fish, though this arrangement also reduces stability compared with lift generated purely by fins.[3]In koi and other members of the superorder Ostariophysi, the swim bladder is also connected to the inner ear through a chain of small bones known as the Weberian ossicles, collectively forming the Weberian apparatus.[4][6] This linkage transmits vibrations from the swim bladder to the inner ear, enhancing the fish's sense of hearing, in addition to the bladder's role in buoyancy.[6]

Positive buoyancy disorder

Positive buoyancy disorder occurs when a koi cannot submerge and instead floats at the surface or on its side, usually due to excess internal gas from an over-inflated swim bladder.[2] Affected fish cannot fully submerge, which exposes their skin to damage and can lead to secondary infections if not addressed, and also impairs their ability to feed even when food is floating nearby.[2]According to Kodama Koi Farm, possible causes include gastrointestinal issues, parasites, a physical shift of the swim bladder within the body, or other unknown factors that hyperinflate the organ.[2] The same source states these causes need to be properly diagnosed and treated by a specialized veterinarian, with possible interventions including surgical removal of tumors displacing the swim bladder or withdrawing air directly from the bladder with a syringe.[2] In the meantime, keepers are advised to keep the fish comfortable by hand feeding and keeping exposed skin moist, using humectants formulated to be safe for koi.[2]

Causes of swim bladder dysfunction

In aquarium fish generally, swim bladder disease can stem from physical abnormalities, environmental conditions, mechanical injury, or inbreeding, and is commonly reported in fancy goldfish and bettas.[1] Reported triggers include intestinal parasites and constipation brought on by high nitrate levels from overfeeding, as well as overeating, low water temperatures, bacterial infections, and other impaired organs affecting the bladder.[1]Kodama Koi Farm lists physical injury, infection, or constipation among the causes seen in koi specifically.[2] Swim bladder problems are also mentioned as a concern that can arise in aging koi, alongside tumors and digestive issues, during the later life stages when activity naturally declines.[7]Swim bladder tissue can also be affected as part of systemic viral disease. In spring viremia of carp, histopathology described by the World Organisation for Animal Health shows changes to the swim bladder's epithelial lining, which shifts from a monolayer to a discontinuous multi-layer, along with dilated submucosal vessels and nearby lymphocyte infiltration.[8] In koi herpesvirus disease, internal signs reported for a related condition include edema, inflammation, and pinpoint hemorrhages across many organs including the swim bladder.[9] Readers can find further detail on these viral diseases at the pages for spring viremia of carp (SVC) and koi herpesvirus (KHV).

Signs and symptoms

A change in swim pattern together with a change in physical shape or appearance are described as the most common signs that a fish is affected.[1] Affected fish may float nose-down tail-up, float to the top, or sink to the bottom, and may show a distended belly, curved back, or impaired swimming.[1] In koi specifically, the most obvious symptom is an inability to swim without great effort, with the fish sitting either at the top or bottom of the pond.[2] General guidance on recognizing abnormal behavior and appearance in koi is covered on the page for signs of illness.

Diagnosis

Because buoyancy problems can arise from several unrelated causes — gastrointestinal, parasitic, infectious, or a physically displaced bladder — sources state that proper diagnosis and treatment should come from a specialized veterinarian rather than guesswork at home.[2] A full diagnostic fish necropsy, as described by University of Florida IFAS Extension, includes examining external tissues and opening the fish to inspect internal organs for lesions and growths, with organs such as the kidney, brain, liver, spleen, and swim bladder sampled for culture or histology as needed.[10] General approaches to diagnosis, including scraping, microscopy, and when to involve a fish veterinarian, are discussed on the page on diagnosis: scrapes, microscopes and fish vets.

Management and treatment

For general aquarium fish, one commonly cited remedy, which can work within hours and may counter constipation, is feeding green peas to affected fish.[1] Fish surgeons may also adjust buoyancy by placing a stone in the swim bladder or performing a partial removal of the bladder.[1] Prevention measures mentioned include keeping the tank as clean as possible, keeping temperature slightly higher than normal to aid digestion, and feeding highly nutritious food.[1] The disease is described as non-contagious, so affected fish can be separated from others to allow dedicated observation and treatment without risk to tankmates.[1]For koi, Kodama Koi Farm notes that a change in diet, or a short pause in feeding (provided the koi is otherwise healthy and had been eating normally), can sometimes resolve excess internal gas if the cause is gastrointestinal.[2] Where the cause is a tumor, physical shift of the bladder, or parasite, treatments mentioned include surgical removal of the tumor, direct withdrawal of air with a syringe, or other treatment decided after proper diagnosis.[2] General information on treatment approaches for koi disease is available on the treatments overview page, and on parasite identification at parasites of koi.Swim bladder changes are one of several internal findings associated with viral and bacterial disease in koi, alongside signs in other organs such as the liver, spleen, kidney, and intestine.[8][9] Conditions presenting with abdominal swelling, such as dropsy, and diseases affecting the gills, such as those discussed on the gill problems page, can sometimes be confused with or accompany buoyancy disorders and may require similar diagnostic workup.[10] Swim bladder issues are also listed among potential age-related concerns, alongside tumors and digestive problems, in koi reaching their senior years; see lifespan and aging for general background on koi life stages.[7]

Common questions

What does swim bladder disease look like in a koi?
Affected koi have difficulty maintaining buoyancy, sitting at the top or bottom of the pond, floating nose-down tail-up, or floating on their side rather than swimming normally.[2][1]
Is swim bladder disease contagious to other koi?
According to a general aquarium-fish source, swim bladder disease is not contagious and will not spread to other fish sharing the same water, though affected fish are often separated to aid observation and recovery.[1]
What causes swim bladder problems in koi?
Reported causes include constipation or gastrointestinal issues, parasites, infection, physical injury, tumors displacing the bladder, or an unexplained hyperinflation of the organ; a veterinarian is needed to determine the specific cause.[2][1]
Can swim bladder disorders be treated at home?
Some keepers try dietary changes, such as a brief pause in feeding or peas for general aquarium fish, but sources indicate that proper treatment of koi, including possible surgery or syringe drainage, should be carried out by a specialized fish veterinarian.[2][1]

References

  1. ^ Swim bladder disease (Wikipedia). Wikipedia. en.wikipedia.org/wiki/Swim_bladder_disease. Retrieved November 2026.
  2. ^ HELP, Is My Koi Sick?!? Diagnose Symptoms & Fish Diseases - FREE Health Checklist. Kodama Koi Farm (koi dealer). kodamakoifarm.com/koi-sick-health-diagnosis-symptoms-diseases/. Retrieved November 2026.
  3. ^ Swim bladder (Wikipedia). Wikipedia. en.wikipedia.org/wiki/Swim_bladder. Retrieved November 2026.
  4. ^ Fish anatomy (Wikipedia). Wikipedia. en.wikipedia.org/wiki/Fish_anatomy. Retrieved November 2026.
  5. ^ Koi Anatomy Explained (+ Free Labeled Anatomy Diagram). Kodama Koi Farm (koi dealer). kodamakoifarm.com/koi-anatomy/. Retrieved November 2026.
  6. ^ Weberian apparatus (Wikipedia). Wikipedia. en.wikipedia.org/wiki/Weberian_apparatus. Retrieved November 2026.
  7. ^ How Long Do Koi Fish Live? What is Lifespan & Growth?. Kodama Koi Farm (koi dealer). kodamakoifarm.com/how-long-do-koi-fish-live/. Retrieved November 2026.
  8. ^ Manual of Diagnostic Tests for Aquatic Animals, ch. 2.3.9 Spring viraemia of carp (WOAH). World Organisation for Animal Health. woah.org/fileadmin/Home/eng/Health_standards/aahm/current/2.3.09_SV…. Retrieved November 2026.
  9. ^ UF/IFAS EDIS VM113: Koi Herpesvirus Disease (KHVD). University of Florida IFAS Extension (EDIS). ask.ifas.ufl.edu/publication/VM113. Retrieved November 2026.
  10. ^ UF/IFAS EDIS FA055: Submission of Fish for Diagnostic Evaluation. University of Florida IFAS Extension (EDIS). ask.ifas.ufl.edu/publication/FA055. Retrieved November 2026.