Can a fish living in fresh water be called seafood? Pangasius (Wikipedia) says:


  Pangasius is a genus of medium-large to very large shark catfishes
  native to fresh water in South and Southeast Asia. 
  
  ...
  
  In 2011, Pangasius was sixth in the National Fisheries Institute’s
  "Top 10" list of the most consumed seafood in the United States.


If I understand correctly, fresh water is not sea water, and has little salt.

So why can a fish living in fresh water be called seafood?

Thanks.
Don't read too much into the "sea"; there's no rule that every word in the language has to stick precisely to its etymological roots.

Seafood just means edible aquatic life, i.e. fish and shellfish in general. It's a food word, not a biology word, and fish on your plate looks pretty much the same whether it's freshwater or saltwater fish, so generally it all gets lumped into one category.