Dave's fresh pasta has a weekly "fish day" when they get a delivery of very fresh fish with a different thing on special each week. I personally haven't tried it - it's delivered by the same fish wholesaler that sells at the Arlington Center farmer's market as well, I believe.

I've actually had pretty good luck at Market Basket on occasion if you happen to be shopping there - certainly if you are buying supermarket-grade fish to begin with you might as well get it at Market Basket where it can be 1/2 or 2/3 the price of other supermarket chains. I have recently gotten whole mackerel there that was shockingly fresh and cheap cheap cheap.