Might be a dumb question....

[George]

The last few levels of classifications of living things are:
Family
Genus
Species

I have been following hybrid fish for a long time now. From what I read, only fish that are in the same genus have a possibility of hybridizing.
For example, lemonpeel angelfish, it is in:
Family: Pomacanthidae
Genus: Centropyge
Species: flavissima
It can hybrid with a a few of species under the same Genus, like C. eibli and C. vrolikii.

Both flame angelfish and emporor angelfish are in the same family, Pomacanthidae, but they are not hybridizing.
HTH