Fish has long been a trendy food item. Five years ago, they were giving monkfish away as an unpopular entrée; today—due to its sudden popularity in Europe and other places—it’s now selling for $12 a pound. In a few more years, it’ll be given away in fish sticks.

Part of this is the real problem of overfishing. As a fish gets trendy, it gets in short supply. As a result, another fish has to be promoted as the newest thing to fill the gaps in the supply chain. This is why swai is now in every store, when a little while ago you never even heard of it.

Another interesting thing the fish industry does is rename a fish to make it more marketable. Fishermen have long given weird or whimsical names to fish, which is a lot of fun until you want to get people to buy it.

In the 1970s, the accurately named slimeheads were re-christened to orange roughy, and sales spiked. Nobody calls them slimeheads anymore.

Want another practical marketing triump? The Dolphin is an easily caught fish, but in the 1980s people upset over the killing of dolphins reacted to the name on menus. Right: fish restaurants, they assumed, were selling mammals. To avoid the waiter rolling his eyes for the fifth time that day, the industry simply switched to its native Hawaiian name of mahi-mahi and the horror stopped. (In other parts of the world, it’s simply called dorado, now.)

The Patagonian toothfish was renamed in the late ’70s to the Chilean sea bass, and a fish that’s neither from a sea nor even bass, or really even from Chile, became one of the fanciest filets you could order in a restaurant.

By the way, the Goosefish is one of the ugliest fishes on earth. But if you called it monkfish, which we talked about above, you can sell it for ridiculous prices. Right: even this fish was renamed.

That can be good for business, but sometimes that’s not always good for eaters. For example, the ubiquitous “white fish” you see on menus could be just about anything. The Czar often asks the waitstaff if they know what the whitefish is: sometimes it’s gizzard fish, sometimes humpback, sometimes sault, or a half-dozen other varieties. If they don’t know, we ain’t eating it.

Another example is the world famous red snapper, which has been terribly hurt by overfishing. As a result, the rockfish was renamed the Pacific red snapper—it’s not even a related species. In fact, rockfish can consist of 13 different varieties of fish, each marketed as red snapper when in fact it isn’t. Make sure the expensive red snapper you’re ordering is real read snapper: it has a distinctive shape and appearance.

Be equally careful with rock salmon, which is not a salmon at all but dogfish, a relative of sharks. This is important to know if you are on a kashrut diet: rock salmon (which can often consist of other fish besides dog fish) is not kosher.

You’ve gathered that this started in the 1970s, and you would be right. But the trend continues unabated to this day. What are the up-and-coming fish rebrands?

Megrim is being marketed as Cornish sole, as if that’s remotely appealing. Even sketchier, the pilchard is being pitched as a Cornish sardine. Frankly, pilchard sounds better to us.

The ratfish is being test-marketed as grenadier, which is a smart idea. And the witch fish is getting attention as Torbay sole, which isn’t bad since witch is part of the flounder family.

Oh, and swai? Swai’s cheap. But Vietnamese catfish, basa, and iridescent shark are quite expensive, which is a shame because they’re all swai… which isn’t a catfish, basa, or shark at all.

And for God’s sake, stop eating tilapia. Not because it’s been rebranded (it hasn’t), but because it’s a nasty poop-eater high in cholesterol and other’s people’s poop. You’ve been warned.