I used to work in a pet shop with the fish, and kept tropical fish at home, and wouldn't really describe sea fish as tolerant. Maybe a very hardy species would be okay, but I was implying that we might be able to think of some crafty way to keep them alive. Even in a gimballed goldfish bowl that had water changed several times a day, you'd still have a hard time.
One idea I had was a small tank with a simple filter running off 12v, that I could keep just one or two freshwater fish in. Without a filter it may be possible to keep a siamese fighting fish alive, because they can take oxygen from the surface, but you'd still have to keep teh water clean and they're picky eaters.
I think the best chance for success would be a molly, because they can live in brackish water (you could get them used to a mix of seawater and freshwater to save your freshwater), they're tough, and they'll eat almost anything, so you could feed them on normal dried food
(or plankton!). They breed pretty prollifically and give birth to live young that are adorable.