If you ever swim in the Amazon and Oranoco Rivers of South America please think twice before urinating in the water. Fish called Candiru or Carnero is attracted by urine smell (urea and ammonia) and it can insert it self into the penis or vagina while urinating. Then penis fish lodges itself somewhere in the urinary tract with its spines and it uses its mouth for feeding by sucking the blood. It is almost impossible for fish to survive inside of the human body. Removal of the fish is extremely hard due to the spines and if problem is not treated it can result in removal of the genitals.
The fish locates its human targets when people urinate near the fish. A well-circulated myth is that the candiru is capable of swimming up the stream of urine in mid-air to a victim standing on shore or a boat, although this assertion is likely false. Nonetheless, there was a case in which the victim claimed that the fish jumped while he was urinating thigh deep. They are also probably not attracted to pure urine. It is believed that they are able to enter a human urethra only when it is expanded during urination.