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Can a Fish in the Amazon Really Swim up your Urethra?


The candiru (also known as the Toothpick Fish or the Vampire Fish) has long been reputed to be capable of swimming up a person’s urethra during urination in affected waters, causing untold physical harm and psychological trauma.

We mentioned in our 7 terrifying small organisms piece that the candiru was known to have gone up the urethra of at least one unsuspecting male. However, there is considerable controversy surrounding that case and others cited before it.

A dramatic two minutes from the BBC. Unfortunately, the clip includes some false information.

The candiru fish lives in certain parts of the Amazon River in Brazil. It is a small fish (the maximum length is approximately 40 cm), but it comes equipped with piercing spines on its head. These spines are used to pierce the soft flesh of the catfish. The candiru enters the catfish through the gills, lodging itself inside, where it goes to work sucking the fish’s blood.

The candiru was thought to be attracted to catfishes because of urea emitted by the fish’s gills. However, after considerable experimentation in a laboratory setting, it was determined that there is actually no chemical attractant, and the candiru tracks its host with its vision alone.

This is a major revelation, as many people considered the fact that urea was an attractant when discussing possible cases of candirus entering a human urethra. If urine doesn’t attract the fish, that goes along way to debunking the “human-as-host” claim.

The legend of the candiru is further complicated by something else: there is only one case that is even somewhat confirmed. In 1997, Dr. Anoar Samad performed a 2-hour surgery on a patient in Brazil, removing something from the patient’s urethra. The patient claimed that the candiru leaped from the water as the patient was urinating, effectively “jumping into” his urethra.

The problem is that basic laws of physics along with the anatomy of the candiru preclude this fish from jumping up a stream of urine into a urethra. There are further problems with this case, including the candiru that was supposedly extracted. Dr. Samad claimed that he had to break the spines of the candiru to extract the fish. However, the preserved candiru that was supposedly the one removed has its spikes intact. Dr. Samad also claimed that the candiru made it to the patient’s scrotum. According to marine biologist Stephen Spotte, who has studied the candiru extensively, the fish does not possess the necessary teeth or burrowing ability to arrive in the scrotum.

Stephen Spotte went on to say that it may be possible for the candiru to end up in someone’s urethra, but the odds are “about the same as being struck by lightning while simultaneously being eaten by a shark.” (see the source here).

At the end of the day, there are many more dangerous things to worry about in the Amazon river, like piranhas. However, we should insert one last word of warning, specifically for the ladies. The candiru has been known to find its way into the female vagina. While it’s unlikely that the fish will make it up the urethra (in fact, almost impossible), it’s not quite a comforting thought to know that you could have a bloodsucking fish in your vagina. Fortunately, there are no reported cases of serious complications in these instances.

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