Does a Fishy Smell Indicate high ammonia and nitrite levels in my saltwater tank?

Very probably. Why did you get a crab and a fish before your tank was set up and cycled? It usually takes 6-8 weeks to cycle a saltwater tank before you add fish. Most non-hermit crabs won't live until the tank has been up and running for over a year because their isn't enough food for them. If you got them from a store I would take them back until you are ready for them. Its not like the store is going to run out of fish between now and the time you have your tank ready.