As I thought... it was the picture that was deceiving me. It is a male GBR.
I can clearly see the black spots now and the black on the dorsal fin. Mine have red on the dorsal fins and on the tail but I thought that yours was shaped like a Bolivian's with almost a "lyretail" shape to it.
Not sure if it is a long finned variety or not because those don't get the "v-shaped" tail that yours has. It is just thinned out bloodlines that is all. (Notice how the whole fish seems to be "stretched"?)
Look for either or both the male and female to start cleaning a surface or pushing sand/gravel around. This is a telltale sign of breeding behavior. My guess is that the male is being aggressive towards the female in an attempt to get her to breed. Mine do this often.
Cories and anything else in the tank will go after the eggs. This includes plecos, cories, tetras, danios, the parents... probably best to remove the fertilized eggs if/when you get them adn put them into a 10 gallon tank.