Candiru – A “Don’t Pee in the Water” Horror Story Debunked


Home / Candiru – A “Don’t Pee in the Water” Horror Story Debunked

Piaractus brachypomus is one of the natural fish hosts of the candiru. The parasitic catfish feeds by attaching inside the host’s gills and consuming blood. Image by Raymond Ellis. CC BY-SA 3.0.

Evidence That the Candiru Attacks Humans

Two hundred years after the first terrifying report of the candiru appeared, we still have no solid proof that it deserves its reputation. There is one case reported by urologist Anoar Samad of Manaus Adventist Hospital in Brazil; however, the case is not documented well enough to constitute proof.

Of this case, Dr. Bauer told Decoded Science:

“I think any interpretation is very shaky… Dr Samad unfortunately did not really do anything that would allow  proof to his claim… The fish has disappeared; the photos could be really anything… At this stage, the claims cannot be confirmed.”

Researchers have not proven how the candiru locates the gill opening of its fish host, but it is true that urea is excreted by fish through their gills, and by humans in the urine. It is also possible that the movement of liquid out through the orifice attracts the fish.

Zuanon and Sazima observed and documented a candiru successfully penetrating a fish host’s posterior nostril (where water is also expelled) and taking a blood meal.

These authors write:

“entry into the nostril is… probably due to the catfish having been starved for… five days. This may shed some light on the occasional reports of candirus entering body openings… other than the gill chamber…, and may perhaps also relate to the highly unusual penetration of the human urethra…”

Swimming Fears: Candiru Infestation Risks

From the evidence, we know that the candiru does sometimes swim up the wrong stream, so to speak, but it appears that attacks on humans, if they occur at all, are vanishingly rare – maybe once every hundred years or so.

For hundreds of years, people have believed the candiru, or vampire catfish, attacks humans. There are no well-documented cases. Illustration by Robbie Cada.


Bauer, Irmgard L. Candiru – A Little Fish With Bad habits: Need Travel Health Professionals Worry? A Review. (2013). Journal of Travel Medicine. 20:2.

Hara, Toshiaki J., and Zielinski, Barbara. Fish Physiology: Sensory Systems Neuroscience. (2007). Elsevier Academic Press.

Zuanon, Jansen and Sazima, Ivan. Vampire Catfishes Seek the Aorta, Not the Jugular: Candirus of the Genus Vandellia (Trichomycteridae) Feed on Major Gill Arteries of Host Fishes. (2004). Journal of Ichthyology and Aquatic Biology. 8:1. Accessed June 26, 2013.

Samad, Anoar. Candiru Inside Urethral.  Urology Clinic. Accessed June 25, 2013.

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