Its a nice female in my opinion. Both females and males in saums can display long finnage although its more common in males. Males in the past that displayed no knochal hump didn't so because of there weak genetics but considering this is a wild saum and genetics shouldn't be an issue so not having any hump at all even at this size says female to me. I also have a saum out of the same wild batch and although he's not as big as yours due to lack of eating for the first month I had him but he's already displaying a nice little hump. Either way its a nice Gt but if its a male then having no hump is the killer for me. I think male gt's with the large hump is the key to a show quality fish. Just my opinion though, good looking healthy fish either way. Here's a pic of a male and female for you.
iam not sure but looking how the top fins taper to a looong point makes me think its a juvi male....think it might be young still...whatever it is a great buy
I've heard many people over several fish hobbiest sites also claim that the dark black spot was a tell sign for a female....I know my female that i used to have looked exactly like this fish, round head and the spot and she had really long finnage. Always thought it was a male until she laid eggs when i had her in my 55. I'm just going off my experience with Saums and from what I've read about them. I could be wrong, it might just be a low quality Gt male with good color.