Your poaching liquid should be heated to a low simmer. Make sure your pan has enough liquid to completely cover the fish. Cook for 5 minutes after adding the seasoned fish fillets. Remove the pot from the heat and cover it for 10 minutes to allow the fish to finish cooking.
Testing your fish with a fork at an angle, at the thickest place, and gently twisting it is the easiest way to detect if it’s done. When the fish is done, it will flake easily and lose its translucent or raw aspect.