Maybe its the color saturation or interpretation by the camera, but that color doesn't remind me of any that I have seen before. It is too dark for the normal color of the fish, and not really the color of a badly traumatized fin, or infected fin. Is that color a reasonable interpretation of what you are seeing?
I have seen fins that have gotten caught in nets and bled within the fin, but it was much brighter, blood red. I have seen infected fins, and they tend to be much darker.
Zone 7 A/B
Keep your words sweet. You never know when you may have to eat them.
Richard