Howard Fischer
Uppsala, Sweden

“[N]o one has stepped forward to observe the candiru’s life cycle in situ.”
– William Burroughs, Naked Lunch

Humans, like other animals, are subject to infections, infestations, colonization, and invasion by a wide variety of organisms. We are preyed on by viruses, bacteria, fungi, protozoans, worms, and insects. We may be eaten by carnivorous species of fish, reptiles, and mammals. One animal with a frightening but undeserved reputation is the candiru (Vandellia cirrhosa)—or cañero, or toothpick fish, a parasitic freshwater catfish that lives in the Amazon basin. It is found in parts of Brazil, Bolivia, Colombia, Ecuador, and Peru. It is feared because of stories that it invades the human urethra. Its usual way of making a living is by parasitizing the gills of larger fish and drinking their blood.

A German biologist in 1829 was told about the candiru’s supposed urethral adventures, and that men in the Amazon tied a string around their foreskin as prevention against invasion. In 1855, a visiting French naturalist was told that the fish ascends a human urinary stream to enter the urethra. In 1886 and 1891 there were witnessed observations of candiru entering a “native woman’s vagina.”¹ One may ask if some European reports of these events were based on a faulty understanding of the local languages.

The most recent report of a candiru’s urethral entry comes from Brazil. The supposed event happened in 1997 and was reported in 2000.² The patient reported that the fish “jumped” into his urethra while he was standing in a river and urinating.^3,4 Dr. Anoar Samad was the Brazilian urologist who posted the case report and some intra-operative video on his urologic practice’s website.

Stephen Spotte, an American marine biologist, went to Brazil to collect candirus and to see Dr. Samad and the surgically removed specimen.⁵ He concluded, firstly, that the fish did not jump or swim against a urinary stream to end up in the urethra. The specimen Dr. Samad showed him was 13 cm long, and its head had a diameter of 11 mm. Spotte thought it would take much force to get it into the urethral meatus (opening).⁶ Urethral catheters used in adult medical practice have a diameter of 4.7 mm (size “14 French”) or 5.3 mm (“16 French”). The largest ones currently available have a diameter of 8.7 mm (“26 French”), but a “34 French” has been manufactured with a diameter of 11 mm.

Dr. Samad told Spotte that the fish chewed through the urethra and found itself in the patient’s scrotum. Spotte states that the fish does not have the right dentition to accomplish that.⁷ Because of these discrepancies and unlikelihoods, the evidence given by Dr. Samad is thought to be fishy. There is no evolutionary advantage for a fish to enter an orifice from which it cannot escape and will soon die.

Dr. Samad became Minister of Health for Amazonas state in Brazil in 2021.⁸A review of the topic⁹ reassures travelers going to the Amazon basin that there is nothing to fear (so far) from this little catfish. Every year about 700,000 tourists go to countries where visiting the Amazon is possible, and candiru stories may simply be “the stuff legends are made of.” No cases of candiru-in-the-urethra have been reported to the US Centers for Disease Control and Prevention.

References

1. “Candiru (fish).” Wikipedia.
2. Anoar Samad. “Casos Clinicos. Candiru dentro da uretra.” Clinica de Urologia Dr. Anoar Samad, http://web.archive.org/web/20040616043555/http://www.internext.com.br/urologia/Casosclinicos.htm.
3. Irmgard Bauer. “Candiru – A little fish with bad habits: Need travel health professionals worry? A review.” Journal of Travel Medicine, 20(2), 3013.
4. “Candiru (fish),” Wikipedia.
5. Stephen Spotte. Life and Legend of the Bloodsucking Catfishes. Berkeley, CA: Creative Arts Book Company, 2002.
6. “Candiru (fish),” Wikipedia.
7. Bauer, “A little fish.”
8. “Anoar Samad anunciado como novo secretário de Saúde de Amazonas.” Estado Politico, June 28, 2021. https://www.estadopolitico.com.br/anoar-samad-e-anunciado-como-novo-secretario-de-saude-do-amazonas/.
9. Bauer, “A little fish.”