So you've had a long day trekking through the Amazonian forest and a quick dip in the cool waters of the river seemed like the best way to remove the sweat and dirt of the day's trekking... unfortunately, unlike Hartlepool Municipal swimming pool, there is no sign telling you not to urinate in the water, although perhaps here it is an even more important rule to obey than it ever is in your local swimming pool back home.

Candiru¹ (also carnero), or the 'vampire fish' of the family Trichomycteridae, is an inhabitant of the Amazon and Orinoco rivers. It is eel-shaped, smooth and slimy, with sharp teeth and backward-pointing spines on its gills. A fast, powerful swimmer, there are two² main species of vampire fish:

1. The finger-sized candiru-açu (whale candiru) is a scavenger that prefers feeding on dead fish.
2. A toothpick-sized species which normally burrows into larger fish, but has gained a fearsome reputation rivalling that of the dreaded piranha. Found only in fresh water, this small (up to 5cms³ in length and four to six millimetres wide) fish is the reason for which you really ought not to pee in the river. It is this little creature which this entry is about.

The candiru is a parasite which belongs to the catfish family. Its modus operandi is simple as well as ruthless. To find a host, the candiru first tastes the water, trying to locate a water stream that is coming from the gills of a fish. Once such a stream is detected, the candiru follows the stream to its new host and inserts itself inside the gill flap. Spines around its head then pierce the scales of the fish and draw blood while anchoring the candiru in place. The candiru then feeds on the blood by using its mouth as a sucking apparatus and while slurping, it rasps with the long teeth on its top jaw. Once fully gorged on blood, it unhooks its spines, wriggles out of the stricken fish and sinks to the bottom of the river to digest its meal.

However, the reason why humans fear the vampire fish is that it is the only fish known to feed parasitically on humans (well, except for the Babel fish of course). The candiru is said to be highly attuned to the smell and taste of human urine. If the fish detects such a stream in the river, it follows the flow back to the human, swims up the urethra and lodges itself somewhere in the urinary tract with its spines. Once safely positioned in the urinary tract, blood is drawn, and the candiru gorges itself on the blood and body tissue. Because its body expands due to the amount of blood consumed, this is a one-way trip for the creature, it's now stuck fast. The candiru can attack both men and women.

Treatment

The pain, apparently, is spectacular. You must get to hospital before your bladder bursts; you must ask a surgeon to cut off your penis.
- Explorer and travel writer Redmond O'Hanlon⁴

This is perhaps one time where it really is most advisable to ignore 'don't panic' advice and instead, panic. Infection by the fish is often fatal if not treated immediately as victims can quickly bleed to death. The only treatment is surgery to remove the vampire fish by amputation of the affected area; clearly this has now made half the audience reading this run screaming in terror from their PC.

Well, 'panic' was advised.

Alternative Therapies

Just on the off-chance that you don't want your penis amputated, there are a couple of other things you can try:

In severe cases the fish has to be surgically removed, but very hot baths have sometimes proved effective, and if any part of the candiru protrudes from the body it can be dissolved by applying a piece of xagua plant⁵.
- Stan Kemp of the Kingfisheries Aquarium, Beckenham, who wrote to the Daily Mail in 1997.

After a candiru has lodged itself, huge doses of vitamin C may soften the spines. Then, you pass the fish.
- Dr Paul Auerbach, author of a popular book on wilderness medicine.

Just when you thought it couldn't get any gorier, fish expert Barry Chernoff says that lodged candiru fish have been known to 'actually chew their way into the testicles'. He describes surgery thus: 'the person has to be sliced open and sewn back up with the hope that everything works'.