First what type of LMB were stocked ? Then if someone can tell they are better than anyone I know. You have to test the genetics to be sure. Sometimes there are visual hints but even then it is a wild guess. If it’s a 15 lb fish then you are fairly sure it has some Fla genes. Here is one way but it may not work for crosses - Count scales on the lateral line. The Fla LMB has 69-73 scales compared to the northern LMB’s 59-65.