Check the fish early and often for doneness. Simple formulas—10 minutes to the inch is a popular one—and past experience can get you in the vicinity of the correct time, but there’s no substitute for checking the particular piece. This can be done by measuring the internal temperature with a reliable thermometer, peering into a small incision to see whether the interior is still translucent or already opaque, pulling on a small bone to see whether the connective tissue has dissolved enough to release it, or pushing a small skewer or toothpick into the flesh to see whether it encounters resistance from coagulated muscle fibers.