Can freshwater fish, crayfish, etc. still be referred to as seafood or is there a special term?
In common usage seafood is any "edible aquatic life" - http://en.wikipedia.org/wiki/Seafood Also a lot of seafood is grown in "farms" so we may have to invent a new term for sea/river/tank foods!
Yes. This article on Britannica online explains.
ARTICLE from the Encyclopædia Britannica
Seafood comprises all bony fishes and the more primitive sharks, skates, rays, sawfish, sturgeons, and lampreys; crustaceans such as lobsters, crabs, shrimps, prawns, and crayfish ; mollusks, including clams, oysters, cockles, mussels, periwinkles, whelks, snails, abalones, scallops, and limpets; the cephalopod mollusks—squids, octopuses, and cuttlefish; edible jellyfish; sea turtles; frogs; and two echinoderms—sea urchins and sea cucumbers.