Nice aquariumm.
But this tank's dimensions are very weird. Don't you think it's too short for silver sharks? This fish is very active... and i think it need at least 80cm tank.
It depends...
Remember that fast fishes need more space...
My suggestion is Danio aequipinnatus... its nice colorful fish and easy to keeping by beginners :)
Nice photos...
Where have you bought the skull? It is very original :) I have never seen skull in aquarium :)
But i think there should be a background...