The striped pangasius, also known as "iridescent shark," is a variety of catfish native to Southeast Asia's Mekong River. Like the American channel catfish, it is well suited to aquaculture and widely grown for both the domestic and export markets. It can't be marketed in the U.S. as catfish since 2002, when a law was passed restricting that label to the domestic species. Unscrupulous importers and fishmongers will sometimes sell them as basa, a related but superior species. Other names for the striped pangasius include swai, the Thai name, and tra, the Vietnamese name.
Rinse the fillets under cold running water and pat them dry with clean paper towels. Lay them out on a parchment-lined baking sheet, spacing them evenly.
Drizzle the fillets with a few drops of lemon juice each and season them lightly with salt and pepper. Dot the fillets with butter.
Preheat your oven to 400 F and slide the sheet of fillets onto the middle rack.
Bake at 400 F for eight to 10 minutes, until the fillet is firm to the touch and beginning to turn from translucent to opaque in the middle of the thickest part of the flesh.
Serve hot with your choice of side dishes.