If i can't eat tuna for its mercury toxicity, what can i eat to have omega-3 since i have ra and taking methotrexte evry saturday & folic every sunday?

Wild salmon,sardines: Tuna is one of the fish with relatively high levels of mercury but many fish are high in omega 3's ; low in mercury including salmon and sardines; avoid farmed salmon due to pcb's. Or you can take fish oil capsules- make sure it is purified to remove mercury and ideally esterified to improve absorption. Flax and hempseed oil are also good. See http://www.Nrdc.Org/health/effects/mercury/guide.Asp.

See details: Studies have conclusively shown that mercury levels in fish are too low to cause any issues in humans.