This marine aquarium at Suntec kept re-stocking their fishes and invertebrates because they had been losing them gradually.
The large fish in the 1st two photos is an Emperor Angelfish (scientific name: Pomacanthus imperator).
In the 3rd photo, another fish was dead and half-buried in the gravel bed.
In the last two photos, the black and white small fish is the 3-Striped Damselfish or White Humbug Damsel (scientific name: Dascyllus aruanus). Don't be fooled by its size, because it is a very aggressive and territorial fish in an aquarium. The orange fish with a vertical white band across its face is the Tomato Clownfish (scientific name: Amphiprion frenatus).
A link on some marine fishes is shown below:
