Tuna is high in mercury. Three fish that are sustainable, low in Mercury, high in Omega3s, rich in protein and very inexpensive: Sardines, herring and mackerel. Mackerel is an easy replacement for canned tuna for tuna salad. Mash up mackerel with a raw egg, oat flower and seasoning and it's a very tasty fish patty when fried in olive oil. I always add a can of sardines to a Caesar salad, my go to lunch. Wild Planet is my favorite brand of sardines, 6 - 4oz cans for $6.49 at Costco.

https://www.healthline.com/health/food-nutrition/11-best-fish-to-eat