Wednesday 18 April 2012

Waiter, there's a fish in my penis

This past week I've been researching and co-writing (with Dan Schreiber of BBC Radio 4's The Museum of Curiosity) the pilot for a new radio series. The show is called 101 People to Meet before You (or They) Die and it's a series of interviews with some of the world's most extraordinary people:  explorers, scientists, artists, philosophers and much, much more. The pilot features Charles Brewer-Carias, the Venezuelan grandson of a British diplomat, who has spent much of his 72 years exploring the Amazon. He holds the world record for making fire using just sticks (2.7 seconds), has discovered over 100 species of plants and animals new to science (of which 20 or more were named after him), and may have discovered the world's oldest life form. He also claims to have found the location of El Dorado, the semi-mythical lost 'City of Gold'.

However, I'm not going to talk about him here. You can listen to the show on Resonance FM on the 30th April instead (I'll remind you closer to the time). What I am going to talk about here is another denizen of the Amazon, the candiru fish. Of all the weird and wonderful things I've had to research recently, this little bugger proved to be the most slippery and difficult to get a hold on.

Candiru, also known as toothpick fish, vampire fish or 'penis fish' are several species of small, thin catfish of the Trichomycteridae family. Although some candiru species have been known to grow to a size of 40 centimetres (16 in) in length, most are considerably smaller. They are best known for their supposed behaviour of detecting urine in water and then following the flow back to source where they enter the human urethra and remain, firmly lodged by way of backward-facing spines. This behaviour is recounted on thousands of websites, in books and on TV shows. A couple of years ago, naturalist Mark Carwardine told the story to Stephen Fry on the BBC TV show Last Chance To See.

As you can see, Stephen does suggest that it's an urban myth but Carwardine assures him that the 'string is a joke but the fish is real'. It was also featured on the BBC's Weird Nature series.

Carwardine is right - the fish is real. But whether or not it actually does what the stories say it does has been the cause of my headaches this week. The truth is somewhat confused.

To begin with, let me say that anecdotal stories about the 'penis fish' go back a long way; right back into the early 19th century. However, and I cannot stress this enough, there are no completely verified accounts of a candiru entering a human urethra. In fact the first documented case of medical removal dates only from 1997 ... and many features of that particular case are somewhat problematic. So, let's look at the evidence for and against the story ...

Over the past two decades, explorers and journalists alike have collected hundreds of tales concerning the candiru's nastiest trick. It's also mentioned in several scientific papers. Professor John R Herman, in his 1973 paper, 'Candiru: Urinophilic catfish - Its gift to urology' (Urology 1(3), pp 265-267), writes:

'One of the strangest [stories from the Amazon concerned] a fish that was urinophilic and could swim up the urethra or into the vagina of the unwary native who urinated while bathing in the Amazon. It was said that this fish, known as candirĂș, was long, thin, and capable of forcing its way into the body's passageways following the trail of urine. Once inside it would eat away the mucous membranes and tissues until hemorrhage would kill it or the host. It was also said that even if one caught the fish by the tail, once in the urethra it could not be pulled out because it would spread itself like an umbrella. Indeed, rumours had it that penectomy was preferred to the misery and pain associated with leaving the fish in the urethra!'

It's notable that Herman recounts the stories but does not provide any actual evidence as proof. Decades before, in a 1945 paper called 'The solution of incrustations in the urinary bladder by a new method', (Journal of Urology, 53(5), p 702) a Brazilian urologist called EugĂȘnio Lins describes a non-surgical method (a herbal mixture at close to boiling point) to treat the condition. He also reports on a US Navy surgeon named Charles Ammerman who operated on three candiru victims, in one case slicing into the bladder to extract the fish. Again, the paper tells the stories but is lacking in details. (Note: I have been unable to find any official record of Ammerman's work. If you can find any such records, I'd love to see them.)

Then there's that 1997 account of the surgical removal of a candiru. In this incident, the victim (a 23-year-old man from Iticoatiara, Brazil, recorded only as 'FBC') claimed that a candiru 'jumped' from the water into his urethra as he urinated while thigh-deep in a river. After travelling to Manaus, the victim underwent a two-hour urological surgery by one Dr Anoar Samad to remove the fish from his body. In Samad's case report we read the following:

'Patient, 23, male, looking for the emergency service with extreme difficulty in urination and bleeding by the urethra, with a history of 3 days that had suffered an attack by a fish of the Amazon region known as the candiru that had penetrated into his urethra when he was urinating into the river. Said that tried to hold it, but it was very smooth and seemed to be of small size. On physical examination, the patient was pale with fever, extreme pain to the manipulation of the penis, urinary retention, bleeding the penis and great swelling of scrotum. Referred to the surgical centre, and under anaesthesia, we performed cystoscopy (endoscopy of the urethra and bladder) for diagnosis and documentation of the case. Identified that the fish was of great size occupying the entire anterior urethra and impacted near the urinary sphincter or muscle that controls urine (Probably as live fish tried to penetrate the scrotal bag, explaining the swelling). We open in the perineum and remove it in this way, but we remove it by endoscopy (sic).'

This appears to be the same story that appeared on a 2010 episode of River Monsters on the Animal Planet channel involving one Silvio Barbosa. Barbosa - presumably Mr FBC - and Dr Samad appeared on the show (you can see an extract here - sadly, Animal Planet has restricted me embedding the video on this blog). Incidentally, you'll sometimes find the following two pictures accompanying the Barbosa story on some websites. They are actually screengrabs from an episode of the US medical drama Grays Anatomy.

As I said earlier, there are a number of problems with this story. Firstly, there's that old chestnut about the fish 'jumping' into the urethra. Research and experimentation with various species of candiru, most notably by the American marine biologist Stephen Spotte, has shown that they simply cannot jump in this fashion. Even if they could, they'd be defeated by simple fluid dynamics; the maximum swimming velocity of the fish is insufficient to oppose the downward velocity of the urine stream, and a fish that size maintaining position and thrust within a 2–7 mm wide column of fluid is simply impossible.

Which brings us to our second issue, the size of the fish. Barbosa describes a 'small fish' but the documentation and specimen (retained by Samad) indicates a fish that was 133.5 mm in length and had a head with a diameter of 11.5 mm. At one point on the TV show, Samad says: I removed the entire fish. It was 6 inch long and about 1/2 inch wide. It would have required significant force to pry the urethra open to this extent. Half an inch? No candiru species has appendages or other apparatus that would allow it to accomplish this, and if it were leaping out of the water as the patient claimed, it would not have had sufficient leverage to force its way inside. This does raise the ugly spectre of possible self-infliction. I am not specifically talking about Barbosa here; I wasn't there and cannot dispute his version of events. But I was a cop for 30 years and in my time I heard any number of stories from hospital staff about people 'falling onto broom handles' or 'sitting on a ketchup bottle' or 'accidentally dropping a knitting needle into their urethras'. Is 'the fish jumped out of the water and forced its way up my willy' in the same camp? It's not without precedent. In a 2007 paper from Indian two surgeons report operating on a youth who claimed that a fish had jumped into his urethra while he was cleaning his fish tank. Presumably while naked.

Thirdly, Samad's paper, and numerous other sources, claim that the fish was attracted to the victim by the scent of urine in the water. Now, it is true that fish excrete ammonia through their gills and the candiru's natural behaviour is to swim into the gill slits of fish and to attach themselves to the blood-rich tissues to feed. Ammonia and urea are dangerous to a fish's metabolism if allowed to build up in concentration inside the body. So urea is released in urine and ammonia is excreted through the gills. Therefore, it seems quite logical to assume that it is ammonia - present also in urine - that attracts the candiru to a possible host, fish or human. However, this was proven not to be the case in 2001 when experiments clearly showed that candiru identify potential hosts by sight, not smell, and have no specific ability to detect chemical attractants.

There are other issues with Samad's paper and the account of the unfortunate Mr FBC but it would take too long to recount them all here. Suffice to say, the story doesn't stand up to scrutiny.

As for other stories of candiru attacks, most are variants on the same theme. In 1855 French naturalist Frances de Castelnau reported that local Araguay fishermen told stories of  a fish that 'springs out of the water and penetrates into the urethra by ascending the length of the liquid column' (Castelnau dismissed the claim as 'absolutely preposterous'). Another account was documented by biologist George A Boulenger from a Brazilian physician named Dr Bach, who examined a man and several boys whose penises had been amputated. Bach believed this was a remedy performed because of candiru, but he was merely speculating as he did not speak his patients' language. American biologist Eugene Willis Gudger later noted that the area the patients were from did not have candiru in its rivers, and suggested the amputations were much more likely the result of having been attacked by piranha.

In 1836 Eduard Poeppig documented an eyewitness account by a local physician called Dr Lacerda, who told of a case where a candiru had entered a native woman's vagina, rather than a male urethra. He relates that the fish was extracted after external and internal application of the juice from a Xagua plant (believed to be a name for Genipa americana). And in 1891 naturalist Paul Le Cointe provides a rare first-hand account of a candiru entering a human body, and like Lacerda's account, it involved the fish being lodged in a vagina rather than a penis. This raises an interesting point; if the candiru's natural behaviour is to parasitise the gill slits of fish, isn't the human vagina a far more likely target than the penis? And yet there are almost no stories of this happening. The aforementioned Dr Eugene Gudger (writing in the 1930s) noted that 'there have been several other cases reported where the fish entered the vaginal canal, but not a single case of a candiru entering the anus'. He therefore concluded that this supports the unlikelihood of the fish entering the male urethra, based on the comparatively small opening that would only accommodate the most immature members of the species.

Perhaps the most damning evidence against the candiru legend is this: these fish are very common and numerous. And considering how many native adults and children spend their days playing, washing and swimming in the Amazon and its tributaries (and not bothering to get out of the water before urinating), there should be numerous documented cases of candiru-plugged urethras. But there aren't. There are almost none.

But you can't keep a good story down and, despite the legend of the candiru appearing to be just that -  a legend - it continues to pop up on websites and TV shows with reckless abandon for the facts. It would be wrong and unscientific to say that there has never been a candiru attack on a penis - as you've seen, there is some evidence (albeit nearly all hearsay) to suggest that it might have happened. However, these cases are so rare and so unlikely that you probably have as much chance of a candiru attack as being hit by a falling meteorite. Certainly, in his deliciously-named book, Candiru : life and legend of the bloodsucking catfishes, biologist Stephen Spotte - who has spent 40 years studying the animal - concludes that lurid tales of the 'penis fish' are almost certainly urban myth.

Which is a bit of a shame because the myth is almost always more entertaining than reality.


Gudger, E.W. (1930). On the alleged penetration of the human urethra by an Amazonian catfish called candiru with a review of the allied habits of other members of the family pygidiidae. The American Journal of Surgery (Elsevier Inc.) 8 (1): 170–188.

Randall, D. and Wright, P. (1987) Ammonia distribution and excretion in fish Fish Physiology and Biochemistry, Volume 3, Number 3, 107-120.

Spotte, S. (2002) Candiru : life and legend of the bloodsucking catfishes. Berkeley, Calif.: Creative Arts Book Co.

Spotte, S., Petry, P., Zuanon, J.A.S. (2001). Experiments on the feeding behaviour of the hematophagous candiru. Environmental Biology of Fishes 60 (4): 459–464

Vezhaventhan, G. and Jeyaraman, R. (2007) Unusual Foreign Body In Urinary Bladder: A Case Report. The Internet Journal of Urology. 2007 Volume 4 Number 2

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