The FDA limits servings for children and people about to become pregnant, but says nothing concerning non-pregnant adults. Do any health organization recommend a limit to the amount of low-mercury fish non-pregnant adults can eat?
Jillian Michaels did a great YouTube video on this in the past year. It lists RDAs for pregnant women and adults as well as a lengthy list of options for low-mercury fish. I believe she discussed other nutrition markers as well. I saw it when I searched YT recently. I think this will at least provide some of the answers you seek.
There is an FDA advisory for all adults (would have to look on their website, but something like 1-2 cans of tuna/week?), but its more of a suggestion, where as for children and planning-to-be-preggers adults its a stronger advisory as their are developmental issues in those cases (children and soon-to-be-children).