Mash together butter, chipotles to taste, adobo sauce, and salt with a fork until blended.
Pat fish dry and cut each fillet in half crosswise, then season with salt and pepper.
Spread flour on a plate and dredge fish, knocking off excess.
Heat 1 1/2 tablespoons oil in a 12-inch nonstick skillet over moderately high heat until hot but not smoking, then panfry fish, skin sides up first, in batches, turning over once, until browned and just cooked through, 4 to 6 minutes.
Transfer as cooked with a slotted spatula to plates and add more oil to skillet as needed.