It's tough for me to tell with the blue tint to the photo and my small phone screen.Nile perch usually have a mottled coloration...It looks a little beat up but nothing too serious,how big is it and if you don't mind how much was it?
The key to id'ing them, for me at least, is that the barramundi have that unique arch from the back down to the head whereas the Nile perch is more of straight line.