i was going to say a deformed trout but the salmon hyrbridization is good as well, i was thinking that the fish was maybe kept in a tank that was too small and bashed its head into the sides but i don't see any scars. fisheries explanation is sound as well, i forgot about them cutting off the adipose fin but they do, there are some dams/fish ladders that have machines that scan and count the number of wild and fishery hatched fish that come through them in order to keep track of the populations.