At the basement of Plaza Singapura near Dhoby Ghaut MRT, there is a new fish shop nested near the escalator at basement 2. This fish shop sells a wide range of both marine and freshwater fishes. Below are some pictures taken from the shop. Due to strong lighting, some of the pictures are not as clear.
Warning: The prices of the fish here tends to be higher than most places, but it is conveniently located in one of the better shopping mall in Singapore where rental is expensive.