From the little I can see it looks more like fin rot, but it could be either or both, too.
If you've seen other fish chasing this fish then you may want to remove this fish temporarily so he can heal. The best treatment is pristine water conditions and Melafix. If the deteriation in the fins suddenly seems to be getting worse, the fins develop a white or gray fuzz, or the fish's behavoir changes, (stops eating, starts hiding), then you may need to treat with an antibiotic.
If you can't remove this fish for treatment and other fish are chasing it then try putting several large fake plants in the tank--just temporarily. It will give him a little buffer from the aggressors.
Robin
If you've seen other fish chasing this fish then you may want to remove this fish temporarily so he can heal. The best treatment is pristine water conditions and Melafix. If the deteriation in the fins suddenly seems to be getting worse, the fins develop a white or gray fuzz, or the fish's behavoir changes, (stops eating, starts hiding), then you may need to treat with an antibiotic.
If you can't remove this fish for treatment and other fish are chasing it then try putting several large fake plants in the tank--just temporarily. It will give him a little buffer from the aggressors.
Robin
