I'm not a fan of goldfish.  Not one bit.  However, a fellow Voorheesian (who now goes by the name Sarcasta) kept a huge fishtank in the lobby of our college dorm, and she loved goldfish (probably still does).  She kept that tank stocked full of several different types, and did all kinds of watercolor paintings of them (she even once had the front of the tank decorated with a string of roughly lifesize paintings that identified each fish by name).  Other than the token plecostemus, however, the only fish that I ever really cared much about was the Black Moor, which another one of our college friends constantly referred to as "eyeball fish".  And so, when I figured out a way to make the tail, this result was inevitable.  Other than that one construction idea, the entire thing is actually a one-day build.  And Sarcasta, if you're out there, hopefully someone will point you this way and you'll get a laugh out of this.