Mix the mushroom soup and milk together. Add the onion ,celery and green pepper. Drain the tuna and flake. Drain the salmon, remove any bones and flake. Add to the mixture. Add the drained shrimp. Add 2/3 of the can of the chow mein noodles. Put in a buttered casserole.Sprinkle the rest of the noodles on top. Bake in a 350F oven for 35 to 40 minutes or until bubbly.