A candiru, also known as Vandellia cirrhosa or the toothpick fish, is a small, scaleless, parasitic freshwater catfish that is native to the Amazon River region in South America. Candiru belong to the family Trichomycteridae, which includes 207 species of parasitic catfish. For some, the term 'candiru' refers to not just one fish, but to all those within the entire genus of Vandellia. Many sources, however, use the term to refer only to Vandellia cirrhosa.
The eel-like fish can grow up to six in (about 15.24 cm) in length, and has a translucent body with a small head. Not much is known about the breeding habits of this fish. It preys on larger fish by drinking their blood, and, after it has fed, its belly can appear bloated and distended.
Its feeding habits have given the candiru an infamous reputation, even more infamous than the piranha. The fish hunts by literally tasting the water. It seeks out its prey by looking for ammonia, a by-product that is expelled from the gills of other fish. When the parasite locates a victim, it forces itself into its victim's gill cavity. Once inside it locks itself in by raising spines on its own gill coverings.
When people swim or wade in the waters these fish inhabit, they should be very careful not to urinate while doing so. Human urine contains ammonia, the chemical candiru use to locate prey. During urination, the urethra expands wide enough to allow urine to be expelled, and allow a parasite to enter.
These fish have been known to follow the path of urine into the urethra of unsuspecting people. For instance, there is a well-known case of a man who had to have a six-inch fish surgically removed from his penis, after it had been lodged there for a few days. The fish have to be surgically removed because the spines on its gills make it impossible to remove the fish by pulling it out.
Another fish known simply as a candiru is the candiru asu, and it is often confused with the parasite that feeds on blood. This type feeds primarily on organs and meat. It has a small, circular mouth that is full of sharp teeth, which it uses to chew a hole in its victim. Once a hole is made, the fish eats its way into the body and consumes it from the inside. These fish will not only eat dead bodies, but any body that is incapacitated in the water.
When bodies are retrieved from the Amazon River, coroners often discover bullet-shaped holes in them. Upon closer inspection, an inspector may find that the body is actually full of these parasites. Some corpses have been found to contain hundreds of these fish.