Actually, there is excellent frozen fish and other seafood available. If you have a large supermarket, they probably have a good selection.
I live where fresh seafood is all around, but believe that properly processed frozen food is better that fresh that hasn't been handled properly.
I work at sea and buy for 45-60 days, so use lots of frozen seafood.
I do use canned clams and do not find them too salty, do not think it would hurt to give them a quick rinse?
This is my opinion, but please stay away from farmed salmon--it is awful tasting and bad in many ways. Also you may want to think of buying fish processed in China, been some bad publicity about that too.
But seafood is so good and good for you,