Aw thanks Ryukin_5, I really didn't know about that one. He's still quite small so I didn't know whether he would have got his 'female' shape yet if he were a girl... if you see what I mean!

AfishIonado (... just an awesome name!) I remember that being one of the reasons when I read up about them ages ago, yeah. I seem to remember that they just aren't very good for certain types of filtration either. Can't remember the details though.