The Candirú or Canero (Vandellia cirrhosa) - also known as the Vampire Fish, is a freshwater fish belonging to the Catfish group. The species grows only to being one to two inches in length and four to six millimeters wide. It is shaped like an eel and is almost completely transparent, making it almost impossible to see in the water. A fast, powerful swimmer, the fish is smooth and slimy, with sharp teeth and backward-pointing spines on its gill. The Candiru is primarily found in the Amazon and Oranoco rivers and has a reputation among the natives as the most feared fish in its waters.
There are 3 main species of Candiru: the finger-sized Candiru-açu and a toothpick-sized species normally burrow into larger fish. The whale Candiru is a scavenger that only prefers feeding on dead fish. Though they live in the river, like most scavengers they do not like the sun and tend to bury themselves in the mud and sand of the river bottom underneath logs and rocks.
The Candiru is a parasite. Its modus operandi is simple as well as ruthless; to find a fish, 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 draws blood while anchoring the candiru in place. The candiru then feeds on the blood by using its mouth as a slurping apparatus and while rasping the long teeth on its top jaw. It then, unhooks its fins and sinks to the bottom of the river to digest its meal. The blood feeding has led to it earning the moniker: the vampire fish of Brazil.
However the reason that the Candiru is most feared by humans is because it is the only vertebrate known to parasitize humans! The fish is said to be addicted to the taste and smell of human urine. Candirus parasitize humans, when they are skinny-dipping while urinating in the water. The candiru tastes the urine stream and follows it back to the human. It then swims up the urethra and lodges itself somewhere in the urinary tract with its spines. Blood is drawn, and the candiru gorges itself on the blood and body tissue, its body sometimes expanding due to the amount of blood consumed.
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. The Candiru can attack both men and women. Penectomy is generally preferred to the misery and pain associated with leaving the fish in the urethra.
One way to expel the fish would be to drink the juice of the green fruit of the Jagua tree, Genipa Americana L. The juice of this fruit is brewed into a tea and drunk hot, supposedly causing the skeleton of the fish to dissolve and resulting in its expulsion from the victim within a couple hours. A synthetic version of the brew has been used in the past by urologists to dissolve bladder "incrustations" and kidney stones. The Candiru can also be removed surgically. But both these processes are time consuming.
There are moves to ban the import of these fish into the United States because of fears that some of them might find their way into American rivers and wreck havoc.
As of now there are no known predators of the Candiru and apart from their feeding habits there is very little information available about them.