Interesting. The first time I've seen it for sale is here though. Never really paid attention to it elsewhere I suppose. Just gotta watch out for them at the sunny beaches of Okinawa.
A perhaps common fish for sale in Japan may be Mako Shark and other shark meat for sushi. I have had shark to eat and it was okay. Sword fish was actually much tastier.
The Japanese continue to set and break record prices for Tuna. Again, any shark caught with their haul may have at one time been slaughtered and thrown overboard. If there is a market for shark then of course they will salvage what they can. If internal organs are of benefit then those will be saved.
Centuries have held the benefit of many animal parts for cures and home remedies, with perhaps China leading the way.
My wife's uncle was set up in a sting operation for transporting bear parts across state lines. There is hardly any part or organ of bear not used for medicinal purposes and fetch mighty high bucks on the black market.
Shark has been used as well for many objects. It is also a quite revered in many other cultures.
The fact that science has found a use for shark is assuring in the sense that those thousands that were slaughtered and dumped may have some market value. No, I am not at all endorsing the slaughter of species.
If there is anything to be concerned about in that regard is the total destruction of plant species that may hold the key to many diseases and the treatment thereof. These talks going on to pay Brazil to save the rainforest is total bullshit - Bribery and Ransom. Plus, it won't work. The price of Gold is too high, the indigent people too poor, and the criminal element too strong to give a rat's ass about trees and plants. All they care about is what is under them in the ground.