Orange Spot Goby question

[rchull69]

I have 2 Orange Spotted gobies in my 180 gal tank. The largest one is about 4 inches long and has a black mark under its jaw and the other is about 3 inches long and has no black mark, just white under it's jaw. Are these markings there to distinguish if they are male or female and if so which one is the male? I was thinking they were like Perculas, the largest being female. Any ideas? Thanks.

[ouccmich]

I've read that females often have black dots on their tail fins, but I'm unsure about marks under it's jaw. Perhaps one of the experts knows.