A tighter shot would help, because with many of the tribe Geophagini, it is small details that make a difference, such as arrangement of spots on the fins .
And if its a female, or immature, its even harder, because on 1st glance, they all look very similar.
Here are some examples.
female Gymnogeophagus balzani
female Gymnogeophagus quilero, male in background
Gymnogeophagus sp Paso Pache, female in background
immature Geophagus red head tapajaros