In the world of science filial designations such as F1 etc exist among hybrids ......
An old post from years back that I made in the Flowerhorn section.
In animals (including fish) the filial (F) designation has nothing to do with whether the parents are "wild", or "pure" or not, it simply denotes the first generation that is produced in a breeding program, and is a system used to keep track of the parental generation.
F1 = first filial, which designates that a fish is one generation away from the parental generation.
F2 =second filial, which designates that a fish is two generations away from the parental generation.
etc-etc
The parents can be related, unrelated, and even different species. The offspring can still be considered F1, which if one wants to get overly technical, in the case of flowerhorns they would be F1 hybrids, the same as the result of breeding a horse with donkey, which is an F1 hybrid Mule.
Not everyone in the fish keeping hobby uses the exact same definition or standards for the filial system that Mendel did, but that doesn't make it wrong.