Snrub - next one you catch measure the mouth gape of horizontal and vertical axis. One thing I am exploring is using the mouth gape to distinguish GSF from other species and hybrids. The GSF of any specific body length should have the largest gape horizontal and vertical compared to pure BG, RES, and the hybrids. I have a pretty good list of mouth measurements for GSF.
Ha! I was posting the information the same time you were making your post. Did not measure horizontal, but did vertical. Also several posts up, I list the mouth gapes of GSF from my old pond. Notice a 6" GSF fish out of my old pond has as big of mouth as the 8" fish out of my main pond. Leading me to believe they are hybrids in the main pond even though they have all the markings of GSF.
