yeah mules are kewl... they dont reproduce though... the main problems with hybrid animals are generally with the 'able to breed' types... this is because the biggest threat posed by hybrids are by the second, third or fourth generation hybrids... by this point, hybrid animals can look like a spitting image of a parent(purebred) or have a perfect temperament for said breed...BUT these fish are NOT a true breed... and when sold to people who think it is a purebred, it will produce bad offspring, or not get along with its 'own' kind, there is also the problem of the size it will grow and the environment it requires to strive. this is a particularly bad problem with animals like fish, many of whom already are already difficult to tell apart, and although might look similar, would require totally different environments... it is perfectly fine to experiment with hybrids in the safety of your own home, with a bit of education, but be prepared to cull your fry, when you cant find a home for them and NEVER let your hybridised babies get into the wrong hands, or give/sell to anyone who wont inform the respective byers of their questionable genetics... even then there is still the issue of a fish jumping from one tank to another and work experience kids at your lfs putting the wrong fish in the wrong tank, and countless other possibilities... in my opinion,with animals as complicated as fish... its generally best left alone.. they do pretty good themselves!