Hepatic Amyloidosis in Koi Fish: Protein Deposits in the Liver

Quick Answer
  • Hepatic amyloidosis is a liver disorder where abnormal protein deposits build up in liver tissue and interfere with normal function.
  • Koi may show vague signs at first, including lethargy, poor appetite, weight loss, abdominal swelling, or sudden decline.
  • This condition is often linked with chronic inflammation, long-term stress, or other underlying disease rather than a single simple cause.
  • A definite diagnosis usually requires tissue evaluation by a veterinary pathologist, often after biopsy or necropsy.
  • Treatment focuses on supportive care, correcting water-quality and husbandry problems, and managing any underlying disease your vet identifies.
Estimated cost: $150–$2,500

What Is Hepatic Amyloidosis in Koi Fish?

Hepatic amyloidosis means abnormal protein material, called amyloid, builds up inside the liver. Over time, these deposits replace healthy liver tissue and can make the liver enlarged, fragile, and less able to do its normal jobs. In fish, amyloidosis is usually considered a secondary problem, meaning it often develops after ongoing inflammation, infection, or other chronic stressors rather than appearing on its own. (petmd.com)

In koi, the condition can be hard to spot early because fish often hide illness until they are quite sick. Some koi show only reduced activity or appetite. Others develop a swollen belly, poor growth, or sudden weakness. In severe cases, the liver may become so fragile that internal bleeding or rapid decline can occur. (petmd.com)

For pet parents, the key point is that hepatic amyloidosis is not usually something you can confirm by appearance alone. Many liver, kidney, infectious, and water-quality problems can look similar in koi. That is why your vet will usually focus on the whole picture: pond conditions, diet, stocking density, physical exam findings, and whether tissue testing is needed. (petmd.com)

Symptoms of Hepatic Amyloidosis in Koi Fish

  • Lethargy or reduced swimming activity
  • Poor appetite or stopping eating
  • Weight loss or poor body condition
  • Abdominal swelling or a rounded belly
  • Pale gills or weakness
  • Buoyancy changes or trouble maintaining position
  • Sudden collapse or death

When signs are mild, it is still worth contacting your vet soon. Fish often mask illness, so a koi that is eating less, isolating, or losing condition may already have significant disease. Abdominal swelling deserves prompt attention because it can be caused by liver disease, kidney disease, infection, reproductive problems, or cancer. (petmd.com)

See your vet immediately if your koi stops eating, becomes unable to stay upright, has marked swelling, shows pale gills, or declines quickly. Those signs can point to advanced organ dysfunction or another urgent condition that needs hands-on assessment. (petmd.com)

What Causes Hepatic Amyloidosis in Koi Fish?

In koi and other fish, hepatic amyloidosis is usually thought to develop after chronic inflammatory stimulation. That can include long-standing bacterial, parasitic, or viral disease, repeated tissue injury, or ongoing immune activation. Amyloid is an abnormal protein deposit, and the liver can become one of the organs where that material accumulates over time. This is why your vet will often look for an underlying trigger instead of treating the liver as the only problem. (petmd.com)

Environmental stress also matters. Poor water quality, overcrowding, unstable temperature, excess organic waste, and chronic social stress can weaken fish and make infectious or inflammatory disease more likely. While these factors do not prove amyloidosis by themselves, they can create the kind of long-term stress burden that contributes to serious internal disease. (petmd.com)

Nutrition and husbandry may play a supporting role too. Koi do best with species-appropriate feeding, good filtration, and enough space. A poor-quality diet, spoiled food, or chronic overfeeding can add metabolic strain, while underfeeding can worsen recovery from other illness. In many cases, hepatic amyloidosis is probably the end result of several problems acting together over time. (petmd.com)

How Is Hepatic Amyloidosis in Koi Fish Diagnosed?

Diagnosis usually starts with basics: history, pond or tank review, water testing, and a physical exam by your vet. Because koi liver disease can look like many other conditions, your vet may first rule out more common problems such as poor water quality, dropsy from kidney disease, parasites, infection, reproductive disorders, or tumors. (petmd.com)

If your vet suspects internal organ disease, they may recommend imaging such as ultrasound, along with sedation for a closer exam. Imaging can help identify an enlarged liver, fluid in the body cavity, or other internal changes, but it usually cannot confirm amyloidosis by itself. (2023.wsava-congress.org)

A definitive diagnosis generally requires tissue evaluation. That means biopsy or, in some cases, necropsy with histopathology by a veterinary pathologist. Special stains such as Congo red are commonly used in pathology to identify amyloid deposits in tissues. Because biopsy in fish can be technically challenging and may not be appropriate for every koi, your vet may discuss whether supportive care, referral, or post-mortem confirmation is the most practical path. (vet.uga.edu)

Treatment Options for Hepatic Amyloidosis in Koi Fish

Spectrum of Care means you have options. Here are treatment tiers at different price points.

Budget-Conscious Care

$150–$450
Best for: Koi with mild signs, pet parents starting with the least invasive approach, or situations where biopsy/referral is not realistic.
  • Aquatic or exotics exam, often by teleconsult support plus local hands-on care when available
  • Water-quality testing and correction plan
  • Isolation or reduced-stress recovery setup if appropriate
  • Supportive husbandry changes, including filtration review, stocking review, and diet review
  • Monitoring for appetite, buoyancy, swelling, and behavior changes
Expected outcome: Guarded. Supportive care may improve comfort and stability, but it usually does not reverse established amyloid deposits.
Consider: Lower upfront cost and less handling stress, but diagnosis remains uncertain and underlying disease may be missed.
Most Common

Recommended Standard Treatment

$450–$1,200
Best for: Koi with persistent swelling, appetite loss, poor body condition, or unclear internal disease where a stronger diagnostic plan is needed.
  • Aquatic veterinary exam
  • Comprehensive water-quality assessment
  • Sedated physical exam if needed
  • Ultrasound or other imaging to assess internal organs
  • Targeted testing for infectious or husbandry-related contributors
  • Supportive medications or treatments directed by your vet for secondary problems
  • Follow-up rechecks and husbandry plan
Expected outcome: Guarded to poor, depending on how advanced the liver damage is and whether an underlying cause can be controlled.
Consider: Provides a more complete picture and may identify treatable contributors, but still may not give a definitive diagnosis without tissue sampling.

Advanced / Critical Care

$1,200–$2,500
Best for: High-value koi, severe or rapidly progressive cases, or pet parents who want the clearest diagnosis and full range of options.
  • Referral to an aquatic or specialty exotics service
  • Advanced imaging and repeated monitoring
  • Sedation or anesthesia for biopsy or minimally invasive tissue sampling when feasible
  • Histopathology with special staining to confirm amyloid
  • Intensive supportive care for severe weakness, fluid issues, or secondary infection
  • Necropsy and pathology if the koi dies or humane euthanasia is chosen
Expected outcome: Usually poor once disease is advanced, though advanced diagnostics can clarify whether another treatable condition is present instead of or alongside amyloidosis.
Consider: Most information and specialist support, but higher cost, more handling, and not every fish is stable enough for invasive procedures.

Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.

Questions to Ask Your Vet About Hepatic Amyloidosis in Koi Fish

Bring these questions to your vet appointment to get the most out of your visit.

  1. What problems are highest on your list besides hepatic amyloidosis?
  2. Do my koi's signs suggest liver disease, kidney disease, infection, reproductive disease, or something else?
  3. Which water-quality values should we test today, and what exact targets do you want for this pond or tank?
  4. Would ultrasound or sedation add useful information in this case?
  5. Is biopsy realistic and safe for my koi, or would the risks outweigh the benefits?
  6. If we do not pursue biopsy, what supportive care plan makes the most sense right now?
  7. Are there signs that would mean my koi needs urgent recheck or humane euthanasia?
  8. What changes to diet, stocking density, filtration, or quarantine practices could reduce future risk?

How to Prevent Hepatic Amyloidosis in Koi Fish

There is no guaranteed way to prevent hepatic amyloidosis, but the best strategy is to reduce the chronic stress and inflammation that may set the stage for it. That starts with excellent water quality, stable temperature, appropriate stocking density, strong filtration, and regular removal of organic waste. Poor water quality is a leading driver of illness in pet fish, even when the water looks clear. (petmd.com)

Quarantine new fish before adding them to the main pond or tank. This helps lower the chance of introducing parasites, bacteria, or viruses that can create long-term health problems in the group. Routine observation also matters. A koi that is eating less, isolating, rubbing, or losing condition should be evaluated early, before chronic disease becomes harder to manage. (petmd.com)

Feed a high-quality diet made for koi, store food properly, and replace old food regularly so vitamin levels stay more reliable. Work with your vet if you notice repeated illness in the pond, because prevention is often about fixing the bigger system rather than treating one fish at a time. (petmd.com)

Find a Vet Near You