The candiru, also called the carnero fish, is a tiny parasitic catfish that inhabits the waters of South America. They can reach lengths of 1-2.5 in (2.5-6 cm) with a width of 3.5 mm. Their diminutive size and nearly transparent body makes them very hard to locate (not that you would want to). The candiru has sharp bones with a series of spines located around the head used while feeding.
The candiru is found only in the Amazon and Oranoco Rivers of South America. They do not like the sun and tend to burry themselves in the mud and sand of the river bottom underneath logs and rocks.
The candiru has a voracious appetite for blood and will parasitize fish, mammals, and humans. One scientist, while holding a candiru, accidently let it enter a small cut on his hand. It could be seen writhing under the skin towards the vein.
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.
When candirus parasitize humans, it is usually only 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 anus and lodges itself somewhere in the urinary tract with its spines. Blood is drawn, and the candiru gorges itself on both the blood and body tissue, its body sometimes expanding due to the amount of blood. This is all said to be very painful for the poor person who has this happen to him or her. Unfortunately, they are almost impossible to remove due to the spines. Amputation of the private areas is the cheapest, and most life-changing, way to remove the fish. Actual surgery is extremely expensive and involves inserting the Xagua plant and the Buitach apple up the urethra. These two plants kill and even dissolve the parasitic fish. If surgery is not done in time, the blockage of the urinary tract will prove fatal. The candiru is the only known vertebrate to parasitize humans.
The candiru has few, if any, enemies at all, as they are feared throughout their geographic range and are given a worse reputation than the pirhana.