This is a question that's been bothering me for a while now.
About 8 months ago, we started getting frozen Basa fillets at work. The box they are shipped in says "Pangasius hypophthalmus." However, we price them as Frozen Basa Fillets (at $1.29/100grams... pretty damn cheap for fish). I decided to Google-Search "Basa Fish" then and saw that it was a type of catfish. I then questioned my boss about it, saying "So basa is catfish, right? I thought catfish was too cheap of a fish to sell here?" (Since I work at a very high-end store) and he was puzzled. "Basa isn't catfish... it's closer to sole than catfish, but quite a bit oilier, like a cod almost. Actually, I don't [censored]' know, I just sell the [censored]." and he laughed.
But now that I finally brought a couple fillets home to try, I'm doing some research before I start cooking it. I remembered that the box had "hypophthalmus" on it, so I Google-Searched "Basa + hypophthalmus" and found a Wikipedia Article on Iridescent Shark.
WTF?
The second sentence explains it all:

This fish is also known as ... striped catfish in the food fish market, and occasionally incorrectly as basa...

So basically it's a catfish, but known as a shark and sold as a totally different fish called basa.

So if you're ever in the market to buy Basa, make sure it's the real Basa, which is VERY hard to find in North America, as 90% of basa sold is actually this "Pangasius hypophthalmus" catfish, when you should be finding the "Pangasius bocourti" catfish.

Then again, you could swing it the other way and say you're having shark for dinner

Dude that is [censored] crazy. The only catfish I eat anymore is flathead river cat. I cant stand store bought/pond raised fish at all. Thats the only thing I liked about my moms Xhusband. He was a commercial fisherman. I think walmart carrys something along those lines in the pets area.