The add doesn't really explain much, how easy maintenance is to perform for example, so any species that requires lots of water changes to keep water quality up, like large cichlids might be too much.
And although total volume is about 150 gallons, it states that capacity is somewhat less (more than 200 liters less).
To me it is probably too small for any sizable fish, so I agree that the best stocking would be species that are best seen from above, and a good choice may be something that schools.
I personally would not put any fish in it that exceed 6 inches.
Depending on the components of the areas tap water, if soft ....a large school of cardinals, or if tap water is harder, a giant school of neons or other such tetras.
If a heater is not desired, a large school of Mountain minnows.