A whole mackerel or bluefish is about 2 feet long, so you will just be able to fit it on an angle in a large rectangular gas grill or a wide oven; see cooks' notes, below. You might want to measure your grill (or oven) before choosing a fish to make sure you'll have enough room.
Active time: 45 min Start to finish: 1 hr
• If you aren't able to grill outdoors, whole fish can be roasted on an oiled large baking sheet (17 by 14 inches) in middle of a preheated 425°F oven, without turning, until just cooked through, 30 to 35 minutes. If fish extends beyond baking sheet, fold up two 12-inch-long pieces of foil and put under head and tail to extend baking surface. • If fish tail begins to brown too much (on grill or in oven), loosely wrap with a small sheet of foil.
