That's hard to tell. Black bar hybrids that will look exactly like a pure black bar endler is quite normal. The phenotypical traits of the black bar endler is dominant in inheritance, wether a pure black bar will be crossed to another endler or a guppy. The exact or similar phenotype of the black bar endler will occur. And "can" already occur in the F1 or later generations.
And those people who claim to see the exact difference between a black bar hybrid and a pure black bar endler are bluffing. I dare to put a pure black bar endler next to a exactly looking black bar hybrid. And you won't see the difference.
Only those hybrid specimens with another kind of caudal (shape and/or color) and/or body coloration are recognizable as being hybrids. Coloration in the dorsal doesn't say anything about the pureness of the specimen. For it's already been known that wild specimens can show coloration in the dorsal as well besides the clear dorsal.
It is...
But also endler hybrids "can" show the endler behavior. That depends per individual specimen wether the endler or guppy influence might be stronger. You can't tell beforehand...
