We started off with salmon and about 1 month after we introduced the other fish, we made sure it was low in mercury. Josh has canned tuna, dover sole, salmon, haddock, cod. Fish is Josh's favorite meal!!!
Here's a list of low in mercury fish
https://www.neiwpcc.org/mercury/mercury-docs/fish_advisory_pdf/VT_eat_fish_low_in_mercury_poster.jpg