Nature - Candiru Fish that Can Climb Your Urethra: Candiru also known as toothpick fish, is a parasitic freshwater catfish native to the Amazon River. Although some candiru species have been known to grow to a size of 16 inches (~41 cm) in length, others are considerably smaller. These smaller species are known for an alleged tendency to invade and parasitize the human urethra. 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. The earliest published report on this candiru attacking human hosts comes from German biologist C. F. P. von Martius in 1829.