Yes... they are hard to sex, the only infallable method is when they are ready to breed, the ovipositor of the male is more pointed that that of the female..... However!!.... (this is not published anywhere and I will not vouch for it) BUT my personal observation is that the distance of the ventrals to the gills in males are shorter than that of a female.... My opinion exclussively, but I have a 96% success rate in sexing them.I'd like to know also. I hear they are quite hard to sex.