I found it. It was near the end of "Exotic Tropical Fishes, Vol. II".
It is called the Candiru (Vandellia Cirrhosa).
Here's an excerpt:
"Natives who do not have any fear whatever for the supposedly, (and on occasion actually) fierce Piranahs, are very cautious where this little devil is concerned. Strangest thing about them is that they seem attracted by the presence of urine in the water and if they find that the odor is coming from a large animal (man included) they will actually force their way, head first, into the urethreal opening. Here the spiny fins prevent the Candiru from backing out and, very unfortunately for its host, the little fish is soon wedged firmly where nothing but a surgical operation...can remove it."
I guess I should have read Wonka's post first before going straight to posting.
Vol. II was originally made up from tear outs that were included in the monthly magazine, "Tropical Fish Hobbyist" for quite a number of years. This is how I accumulated my volume. They stopped putting the tear outs in the Magazine in the early eighties. It's hard to tell exactly when the sheet on the Candiru was printed, but it was known for it's peculiarity well before then.