Rinse the smelt thoroughly and pat dry. Combine the breadcrumbs, salt, and pepper in a large ziptop bag. Place the lemon juice in a shallow dish. Dip the smelt into the juice and then place in the bag with the dry mixture and shake until the fish are well coated.
Place enough peanut oil in a 12-inch cast-iron skillet to just cover the bottom. Set over medium-high heat until shimmering. Add the smelt to the pan, 4 to 5 at a time, being careful not to overcrowd the skillet. Fry until lightly browned and cooked through, 3 to 4 minutes per side.