No way to tell from photos at that age/size, it has not yet developed gender difference characteristics. Maybe at 6 or 7 inches they "might " become obvious, but even as adults its often hard to tell.
If you want to know because you want to spawn them, you best option would be to get 5 or 6 more and let them pair up naturally. Getting only a two, to find a pair is usually not a good route to take.