Haff Disease: Why Cooked Fish Can Still Destroy Your Muscles
Published: October 10, 2026 author: Science Guide Wwai
Seven people sat down to a family dinner in Heyuan, Guangdong. One wild carp — about 2.5 kilograms, caught that day from a local reservoir — was served half raw, half thoroughly cooked.
Five people ate the fish. Some had only the cooked portion. All five ended up in the hospital with their muscles dissolving. The two who never touched the carp were completely fine.
This is Haff disease: a mysterious condition where eating certain fish or shellfish triggers rhabdomyolysis — your own skeletal muscle cells break open and dump their contents into your blood.
And the most dangerous part of the story? Cooking doesn't reliably protect you.
What Haff disease does to your muscles
The name comes from the Haff (Frisches Haff) lagoon on the Baltic coast, where the disease first appeared in 1924. Hundreds of healthy residents suddenly developed severe muscle pain, stiffness, and weakness after eating local fish; some passed urine the color of soy sauce. The cause could not be identified, so the disease was named after the place.
The mechanism itself is well understood. Skeletal muscle is made of long muscle fiber cells. When those cells are badly damaged, their membranes rupture, and their contents flood into the blood — including creatine kinase (CK) and myoglobin.
Myoglobin is the dangerous one. It passes through the kidneys into the renal tubules, where it can form casts that block the tubules. The result: muscle pain and weakness, dark tea-colored urine, and in severe cases, acute kidney injury that can require dialysis.
Haff disease is diagnosed mainly by the pattern: sudden unexplained rhabdomyolysis, CK sharply elevated, and a meal of fish or shellfish within the past 24 hours — after excluding exercise, trauma, and drugs.
For a sense of scale, here is what a lab report looks like when muscle cells break open: after one episode of overtraining, the author's own creatine kinase hit 14,290 U/L — 87 times the upper limit — while AST, CK-MB, and LDH all ran high. In the Guangdong cluster, patients' CK reached 6 to 65 times normal.
Test
Result
Flag
Reference range
Unit
AST (aspartate aminotransferase)
231
High
15–46
U/L
Potassium (K)
4.12
Normal
3.50–5.50
mmol/L
Sodium (Na)
138.2
Normal
135.0–145.0
mmol/L
Chloride (Cl)
100.1
Normal
96.0–108.0
mmol/L
CK (creatine kinase)
14,290.0
High
55.0–170.0
U/L
CK-MB (isoenzyme, dry chemistry)
62
High
0–16
U/L
LDH (lactate dehydrogenase)
767
High
120–246
U/L
AMYL (serum amylase)
63
Normal
30–110
U/L
The Guangdong cluster
In April 2026, a family of seven gathered for dinner in Longchuan County, Heyuan. The report, published in China CDC Weekly, found the first case fell ill at 00:40 and the last at 09:40 the same morning — a median incubation of 11.3 hours (range 4.2–13.2).
All five who ate the red-tailed carp developed vomiting, abdominal pain, and muscle soreness. Their creatine kinase levels reached 6 to 65 times the upper limit of normal; four met the clinical criteria for Haff disease. The two who didn't eat the fish had zero symptoms.
Three of the five patients had eaten both raw slices and cooked fish; the other two ate only cooked fish. They still got sick — a strong sign that bacteria or parasites in raw slices were not the whole story.
Even the fishing itself was strange. The fisherman who caught the carp also ate two smaller red-tailed carp from the same water that day — and never got sick.
All five patients recovered after supportive treatment. It was the second documented carp-linked Haff disease cluster in China, and the first in the Dongjiang River basin.
Why cooked fish can still sicken
The idea that "thoroughly cooked is safe" is the most widely repeated piece of advice about Haff disease — and the evidence keeps contradicting it.
In the United States, the 1997 outbreak involved six people who ate buffalo fish that was either fried or simmered for three and a half hours into fish balls. All 12 U.S. cases reported since 1984 involved cooked fish, according to CDC tracing.
When Chinese investigators screened the Nanjing crayfish outbreak, they tested more than 900 chemical substances — pathogenic bacteria, heavy metals, pesticides, antibiotics, additives. Nothing matched.
The leading suspect is a heat-stable, lipid-soluble toxin that accumulates in aquatic animals through the food chain. In 2022, a Brazilian study detected mass-spectrometry signals consistent with palytoxin and palytoxin-like compounds in cooked fish samples from Haff disease outbreaks. It's the best candidate so far — but still unproven, and different regions may involve different toxins.
The 102-year-old mystery
From the Baltic coast in 1924 to Guangdong in 2026, no one has isolated the actual poison. For a century, modern medicine has failed to name the culprit.
The academic consensus so far is limited to three points: some heat-stable muscle-toxic substance is likely behind it; certain fish and crustaceans can carry it; and both fully cooked and raw consumption can trigger the disease.
That's why Haff disease is sometimes called "a diagnosis like a basket" — anything that fits gets thrown in.
Why crayfish get the blame
Haff disease isn't only about fish. In China, most documented cases with a clear seafood history involve crayfish.
The numbers: a 2010 Nanjing restaurant meal left 2 of 500 crayfish eaters with Haff disease — about 0.4%. An Anhui outbreak in 2016 totaled 672 cases, and the investigation found two independent risk factors: eating more crayfish, and eating the hepatopancreas (the "crayfish butter"). One Nanjing case-control study found people who regularly ate the hepatopancreas had 18 times the risk of those who didn't.
Researchers tallied 1,437 crayfish-linked Haff disease cases in China from 2000 to 2020, concentrated in the middle and lower Yangtze region.
How to eat fish without panicking
Haff disease is genuinely rare. One dinner doesn't mean fish is off the table — freshwater white fish is an excellent protein source, and the sensible move is to keep eating it with judgment.
Three things actually matter: source, part, and amount.
Buy seafood with a clear, traceable origin. Avoid wild freshwater fish from unknown reservoirs, river channels, and ponds — you can't tell contamination by eye. Cook fish thoroughly anyway; it won't reliably prevent Haff disease, but it sharply cuts the risk of parasites and common pathogens. And be cautious with concentrated organs like crayfish hepatopancreas, where toxins accumulate.
Finally, know the warning sign. Haff disease doesn't always produce soy-sauce-colored urine. If you eat fish or shellfish and develop unusual muscle pain within hours to a day — pain far beyond normal fatigue, especially in both sides of the body — go to a doctor and check CK, kidney function, and electrolytes. Severe rhabdomyolysis can threaten your life, and every minute counts.
The bigger idea
Haff disease has been around for 102 years, and the only certainty is that the uncertainty persists. The same dinner that produced five cases left the fisherman untouched. A "toxin list" of dangerous fish doesn't exist — worldwide, freshwater, saltwater, farmed, wild, raw, and fully cooked have all been implicated.
So eat fish, but eat it smart: known source, cooked, no risky organs, and if the muscles ache strangely after dinner, don't wait for the urine to turn dark.
After all, as the Chinese saying goes — you never know what's hiding behind the next meal.
And under the microscope, the story looks different again — including a skeletal muscle specimen where muscle fiber morphology, striations, and nuclei are clearly visible. Search "WWAI" in your app store and download it today.
Buchholz U, Mouzin E, Dickey R, et al. Haff disease: from the Baltic Sea to the U.S. shore. Emerging Infectious Diseases, 2000.
CDC. Haff Disease Associated with Eating Buffalo Fish — United States, 1997. MMWR, 1997.
Lu L, Luo W, Guo H, et al. A Cluster of Haff Disease Associated with Consumption of Cyprinus carpio rubrofuscus — Heyuan City, Guangdong Province, China, 2026. China CDC Weekly, 2026.
Ma H, Wu J, Qin W, et al. Outbreak of Haff Disease along the Yangtze River, Anhui Province, China, 2016. Emerging Infectious Diseases, 2020.
Cardoso CW, et al. Haff Disease in Salvador, Brazil, 2016–2021: Attack rate and detection of toxin in fish samples. The Lancet Regional Health – Americas, 2022.
