The Candiru, also known as toothpick fish or vampire fish, are a number of genera of parasitic freshwater catfish in the family Trichomycteridae; which are native to the Amazon Basin. Some candiru species have been known to grow upwards of 40 centimetres (16 in) in length, but most are considerably smaller. These smaller species are known for an alleged tendency to invade and parasitise the human urethra; however, despite ethnological reports dating back to the late 19th century, the first documented case of the removal of a candiru from a human urethra did not occur until 1997.
Candirus are small catfish. Adults can grow to around 40 centimetres (16 in) with a rather small head and a belly that can appear distended, especially after a large blood meal. The body is translucent, making it quite difficult to spot in the turbid waters of its home. There are short sensory barbels around the head, together with short, backward pointing spines on the gill covers.
Candirus inhabit the Amazon and Orinoco basins of lowland Amazonia, where they constitute part of the Neotropical fish fauna. Candirus are hematophagous and parasitize the gills of larger Amazonian fishes, especially catfish of the family Pimelodidae (Siluriformes).
It was also once thought that the fish was attracted to urine, as the candiru’s primary prey emits urea from its gills, but this was later discredited in formal experimentation. Indeed, the fish appears not to have any response to any chemical attractants, and primarily hunts by visual tracking. 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.
To date, there is only one documented case of a candiru entering a human urinary system, which took place in Itacoatiara, Brazil in 1997. The victim claimed a candiru “jumped” from the water into his urethra as he urinated while thigh-deep in a river. After traveling to Manaus on October 28, 1997, the victim underwent a two-hour urological surgery by Dr. Anoar Samad to remove the fish from his body.