If you're going to travel to the Amazon area, you could be taken by surprise by the fact that it's not piranha the one that causes dread amongst locals. Nor the terrible electric eel, or other monstrous fishes or the powerful black cayman. The real fear of bathing into the river is caused by a fish not longer than 17 cm (7 inch) and just 4-6 mm wide.
It is the Vampire Catfish, Candir￭ or Canero (Vandellia cirrhosa). This fish looks like an eel larvae, being almost completely transparent, and impossible to see in clear water, not to mention the turbid water of the Amazon.
When resting, candiru stays buried in muddy bottoms. A fast, powerful swimmer, the fish possess sharp teeth and backward-pointing spines on its gill's opercle.
The candir￭ is a parasite fish, that attacks the gills of large fish. It enters into the gill cavities of other fish during ventilation of the latter, erects the opercle spine to get stuck, and the host's blood is pumped into its gut by the host's blood pressure. That's why all it needs are just needle-like teeth to make an incision in an artery, without sucking/pumping mechanisms.
For feeding, candiru requires just 30-145 seconds. The same job is done by all its relative species. But candiru goes a little further.
If a bather is naked, candiru can enter into one of his/her body orifices (the vagina, rectum, or even the penis-and deep into the urethra) and due to the opercle's spines protruding from the fish, it is almost impossible to take out the fish, except through surgery. The fish probably takes the urea for water expelled from gills.
The fish tracks down its host by following a water scent to its source and urinating while bathing increases significantly its chance of entering in a human urethra. That's why Indians bathe facing the current, decreasing candiru's chances of entering in the rectum, while penis or vagina are covered up with the hands.
Locals employ against candiru two plants, the Jagua or Huito (Genipa americana) and the Buitach apple, whose mixed extract will kill and after that dislocate the fish. But often enough, the infection causes shock and death of the victim before the candir￭ can be removed. Even if candir￭'s attacks on humans are known, it is not proven that the fish can actually survive once inside the human body. Some countries, like the US, prohibit the importation of candiru.