On the Internet you can find a story that supposedly fish live in the waters of the Amazon, which can enter the body of an unwary swimmer through the urinary tract. We decided to check how reliable this story is.

About the dangerous Amazon fish regularly write bloggers, Media, resources about animals portals with interesting facts, users entertainment sites And services questions and answers. The assertion that it is able to enter the human body through the urinary tract, mentioned even in the authoritative Encyclopedia Britannica. In some sources emphasizedthat residents of the areas where this fish lives swim only in tight-fitting swimming trunks.

This insidious behavior is attributed to the common Vandellia, a small freshwater fish from the order Catfish, also known as candiru. Representatives of this species usually grow to 4–8 cm in length (but can reach 20 cm), have a translucent elongated body and characteristic spine-like outgrowths in the area of the gill slits. The presence of these thorns due to parasitic way of life: the candiru swims under the gill covers of larger fish, anchors itself there with the help of these outgrowths, which simultaneously rupture the vessels of the prey’s gills, and feeds on its blood. The parasite is believed to be a potential host finds by the content of ammonia in water, which is released during respiration. The same substance is also found in human urine. Therefore, some are afraid that its smell may attract the candira, and it will climb into the urethra, vagina or anus.

About the attacks of this fish on people in his books and reports told also European travelers, naturalists, doctors and missionaries who visited the Amazon in the 19th century. In 1930, American biologist Eugene Willis Gudger published in the American Journal of Surgery, an article summarizing previously described cases. The scientist’s predecessors, with reference to Amazonian fishermen, spoke, in particular, about individuals that jumped out of the water and ascended into the human body through a stream of urine (in the 19th century, the candiru even offered call Urinophilus diabolicus - “devilish lover of urine”, lat.). Some victims allegedly had to have their penis removed because of a fish stuck in the urethra. To prevent accidents, local residents, as Gudger points out with reference to predecessors, either tied the stretched foreskin with a cord so that it covered the urethra, or used special sheaths for the penis and vagina. At the same time, the biologist noticed that in the previously described cases, patients with an amputated penis did not live in the candiru habitat, and from this he concluded that the injuries were probably caused by another fish (for example, a piranha).

Similar work was carried out 80 years later by Irmgard Bauer, a researcher at Australia's James Cook University. Having studied the testimonies of travelers, she came to the conclusion that the authors did not see the candiru attacks themselves, but only retold stories from the words of guides and/or local residents. On the one hand, they could embellish the situation; on the other, translation errors were possible. Bauer also emphasizes that the laws of physics will prevent the fish from getting into the urethra by climbing up the stream of urine. Although more than a dozen cases of attack were described in the 19th century, in modern times, the researcher emphasizes, such injuries have not been recorded - with one exception.

In 1997, a man named Silvio Barbossa went to a Brazilian hospital. According to the patient, when he was urinating while standing in the water, he was attacked by a candiru - a fish jumped out of the water, climbed up the stream of urine and climbed into the unfortunate man’s urethra. Local doctor Anoar Samad surgically removed the parasite and preserved it in formaldehyde. This case interested the American biologist Stephen Spott, who went to Brazil and disassembled that incident. In particular, the researcher studied the operation protocol, other documents related to that case, and the preserved body of the candiru. Spott discovered a number of serious inconsistencies:

- firstly, the patient claimed that the fish jumped out of the water and climbed up the stream of urine, although this contradicts the laws of physics;

- secondly, the diameter of the head of the sample preserved in formaldehyde was 11.5 mm, while the diameter of the urethra in men is usually located within 5–7 mm (and it is unclear how a fish that jumped up and moved against the stream of urine could push the urethra apart to get inside);

- thirdly, how showed experiments conducted after the alleged attack, but before Spott's research, the candiru does not respond to the smell of ammonia, so human urine could not be used as bait;

- fourthly, although in the report on the operation the Brazilian urologist indicated that in order to remove the fish from the patient’s urethra he had to remove the spines from the fish, they were in place in the sample preserved in formaldehyde.

By assessment Spotta, the probability of being attacked by a candiru while urinating in water that is teeming with these fish is equal to the probability of a person being struck by lightning while being eaten by a shark. However, despite these inconsistencies, the researcher does not comment in any way on the veracity of the story he studied.

A few years later, Barbossa and Samad starred in a video in which they told their version of the attack to the candiru, and also described the process of extracting it. The original operation was not filmed; the corresponding fragments of the narrative are accompanied by a video of the use of endoscopic technology.

There is no other contemporary evidence of candiru attacking humans. In 2021, Brazilian scientists described a new species, the representatives of which are much larger (their length reaches 30 cm) and feed mainly on carrion, but can also attack humans. True, due to its size, such a fish will definitely not be able to get into the urethra.

Thus, claims of Amazonian fish getting into the human urinary tract are based on the accounts of 19th century travelers, who, in turn, referred to local residents, but never witnessed such attacks themselves. In recent decades, there have been no confirmed candiru attacks on humans.

Cover image: PISCES Conservation Ltd.