Trent surprised me but the fact that it is an ethnic food, it seems, makes sense. No widespread availability / popularity.
Do correct me if I am wrong, but I've read that swai is the iridescent shark catfish meat, Pangasianodon hypophthalmus, not gigas aka MGC or Mekong Giant Catfish. It says so on some packages of swai too. People appear to struggle to ward off complete extinction of the MGC both in the wild and in farming operations. Hardly would MGC be available as a food fish. It may be. I am just thinking aloud. Or its hybrid is.
Viktor I'll have to see if I still have the pic from Central market, they were skin on fillets from approx 18" TSN's only place I've ever seen them was for the Brazil festival event at the store in Dallas Fort Worth. It was cool to see and I regret not picking some up to compare against our local Channel Cat fillets.
You're right on the ID sharks/Striped Pangasius being Swai, I was going to mention that but you beat me to it. They are farm raised all throughout Thailand and Vietnam for food consumption and for fishing parks. Mekong Giant Catfish (Pangasius Gigas) are generally only farm raised for fishing parks to my knowledge overseas not food consumption so limited volume. The government also farm raises them for re-introduction purposes into the Mekong and Chao Phraya Rivers since they are critically endangered in their native range.