The hybrids are hybrids. There is no undoing it and no such thing as a little bit. It's like being a little bit pregnant.
The only way to know that you are not buying a hybrid instead of a "pure" endler is to buy one from a registered breeder of pure endlers. There are 3 classes of endler out there which are as follows.
There are class Ns which can be traced back to the point of collection. These are not necessarily wild but are derived completely from wild stock. If I take some wild endlers and select what I like from them in terms of features, I may be able to develop something that breeds true but it will all still be endler with no addition of guppies or other fish and will be a class N. Class N endlers are derived only from known wild collected endlers or their direct offspring. I have a small breeding colony of this type and am working on line breeding some to develop a long lower red sword and a snake chest in the eventual line if I can get it established. If not, I have not ruined my class Ns by letting them breed with guppies.
There are class P endlers. These I think of as Probably endlers. People like Adrian Hernandez will tell you that your fish looks like it's a pure endler but without being able to trace it you will never know and Adrian will never tell you it's a class N. He will call it a class P if it has all the classic characteristics of an endler.
Then there are class K endlers. Adrian sells these by the truckload. They are known hybrids between class N or P endlers and guppies. They can be very attractive but are pure only in the sense that they will breed true to the characteristics that you thought you were buying. If you wanted a delta tail and a particular color with maybe a top and bottom sword and someone has developed a line of class Ks that breeds true to these characteristics, you can expect any you get to also breed true to type. They are pure in the sense that they won't give you wierdly unexpected results when you breed them but they are still class K hybrids.
Begin pet peave:
Any of the endler classes can be very attractive fish but you should not pay a premium for class Ns unless the person can show that they indeed have and breed class Ns. In my opinion, too many of the fish we see in the hobby today are class Ks that have been sold to an unsuspecting hobbyist as pure endlers. This leads to statements like that a particular color morph is the only "pure" top sword. In reality there are several nice class N top swords and several class K top swords but he has only seen one and was convinced by whoever had it that it was the only kind. That would be like saying that only a red tailed delta guppy was a real delta guppy. Sorry but endlers have a very diverse genetic pool as long as we don't let them all die out or get crossed to guppies.
Sorry for getting carried away.
End of rant.
