That's true spiny dog fish, European conger plus a few more odd fish were sold as "Rock salmon". Growing up Rock salmon used to be my faverite "fish and chips" NOW these less desirable fish species can not longer collectively be called Rock Salmon beause of EU regulations that consider the term Rock slamon as misleading the public to think that the fish is actualy salmon. What a load of BS - NOBODY thought it was salmon, everybody knew it was the junk fish of the catch which made it a cheaper option then cod and plaice and that they tasted prety good coated in beer batter.