Souzai Saishuka no Isekai Ryokouki - Ch. 63 - Port City Danushe

[hanfeizi]

Soup most likely, fin soup is eaten in Japan and China.

That will be a really bad idea....

Spoiler: Soup?

 

[JACGohu]

Eat.
Pretty common outside US, though it is often sold under alternative names, like "Rock Salmon" in UK, "Flake" in Australia, "Cação" in Brazil and Portugal, "Cazón" in Spain, "Tollo" in Peru and "Spinarolo" in Italy. Asia and Africa in general are also large markets for it.

Fins can also be used in soup. As Tsuki09 said, Shark's Fin Soup is a fairly common offering around Asia, largely in places with a Chinese community, which also likely influence local cuisines.

 

[Hoezell]

Well the rock salmon is more specifically the dogfish or 'Squalidae'

Although having vulnerable status (and critically endangered around Europe), Dogfish sharks are one of the only sharks that can be raised in a controlled environment (aquaculture).
Not being apex predators also contributes to lower mercury concentrations on it's meat, one of the reasons it's the most eaten type of shark by far.