The fish you speak of, not the genital eater but the other, is known as the Candiru. It is a parasitic fish that lives in the Orinoco and Amazon Rivers of South America. Mostly known to prey on other fish it sometimes goes after humans. Normally it follows the warmth of water exiting the gills of other fish (or so I believe) where it attaches its self to the gills to draw blood. Sometimes it confuses a human urine trail with its intended prey. This is the grusome part, then there are two schools of thought on entry of this little fellow. The first it that it squirms right up the urethra and lodges its self there. The other which seems to be the most accuarate is that it burrows in through the anus and lodges its self in the urinary tract. Either way it gets in there it doen't want to come out this is because of the spines around its gills that dig into the sides of you know where making extraction difficult. Amputation is easiest or there are herbal remidies made by native to the region that are said to disolve the critter. Anywho the fish is real but only a problem if you like to dive these rivers. But ladies, the little guy goes after you too so look out.
You can find tons of information of ths fish on the web by searching Candiru, but there is a lot of folk lure about this little fishy too.