I love blacktip sharks and would gladly give my left nut to have one, but seeing as how that tank is not big enough to keep that shark for life, it could certainly be put to better use. I can think of a variety of freshwater monsters that would make a much better display than that.
I'm thinking:
aros
lince catfish
ripsaw catfish
dats - widebar, thinbar, NGT
pbass - monos, orinos, tems, azuls
school of black-barred red hooks
gars
dorado
and 1 arapaima
EDIT: How could I forget clown knives, regular and royal