I rarely see a longer operculum flap on a GSF. This fish has a fairly lengthy one, like a larger male BG might, indicating BG genetics. It is also rounder, as has been pointed out again indicating some BG genetics. I do agree that mouth appears a bit smaller than normal for a pure GSF. A pure GSF of that size would have a substantial gape, that fish doesn't seem to. A more in between mouth size, again leaning towards BG genetics. The last thing that gives me the impression of hybrid is the bluish bottom of the operculum. The coloration that gives BG their common name. In GSF, that area of the operculum is generally white(female) or yellow/orange(male), not blueish as in this fish. GSF have very wide ranging coloration though among different populations and even different fish. However, put those four together, the longer operculum flap, the rounder shape, the mouth which seems too small and the wrong coloration and I am saying hybrid.
However, the fact of the matter is without looking at the gill rakers and even genetic testing we'll never know who is right. It really doesn't matter though, as it's one fine fish either way.
