All the "obvious signs" tell me that it's a female but I've seen a "female" with a pink belly before spawn with an undoubtedly male ram producing wigglers. I'm just puzzled by the lack of coloration on the fish. It's not immature because it looks fairly large and appears to have the shape of a female, front dorsal rays of a female, pelvic fins appear short, though not clear and that indicates female, and shape of the head indicates female as well. The actions by the male in the tank indicate a threat so this would imply female or possible the male was previously paired and isn't accepting of this new female. It does happen, and if this is the case he may never spawn with this "female".