I too am not a fish pathologist, but I have seen a few disease problems mainly due to my learning curve of making mistakes at animal husbandry, and the fact that I have so many different species in my ponds. I've done everything wrong -- subsequently stressing my fish, and now the only thing left is to know what I shouldn't do!
IMPO, what I am seeing in the picture is an aeromonas bacterial ulcer more specifically caused by aeromonas hydrophila. also known as MAS (Motile Aeromonas Septicemia), Hemorrhagic Septicemia, Red Sore Disease or Ulcer Disease as Bill says.
It's umbiquitous in the water or digestive track of the fish, and only causes problems when the fish are stressed. It could be aeromonas salmonicida (furunculosis), but I seriously doubt it as it's not that common in warmwater fish, and the ulcers do not fit the description. I could be wrong of course.
Here's a link that may be of interest:
http://aquanic.org/publicat/state/il-in/as-461.pdf If the tail in the pic was that split up when you got the fish, then your fish were severely stressed before you ever got them. If that is the case I would have a word with your supplier and let them know you are not happy. May not help much but it will put them on notice.
Like Bill says the disease will have to take it's course and some will not make it and some won't. However if they are still feeding you could feed them medicated feed if you want to go that route. You can get 50 lbs. of medicated feed from Zeigler Brothers in Gardner PA for about $50.00 which would include UPS shipping. You would have a choice between terrimycin (oxcytetracycoline) or Romet which is a more broad spectrum antibiotic. Terrymycin has to be fed for 10 days while Romet only requires 5 days. Freeze what you don't use and save it if you ever have any problems in the future.
Their website is:
http://www.zeiglerfeed.com/ Be aware though you will be treating the fish that are not that sick yet as the sick ones probably won't eat anymore.
And one more thing: The feed is only available as sinking feed as the heat used to produce floating feed is not conducive to the antibiotics.