I don't know if it is the cause or not, but you mentioned that the fish had been in a show about 10 days ago. Shows are very stressful for the fish, both in getting them there and getting them home, plus the water quality being less than ideal at the show. I would keep an eye on the fish, allow for the stress levels to go down and see if that is what the problem is. Also, if it is stress, I know some like to use some salt, as it does tend to reduce the stress, but be careful as salt is irritating and will cause the same veining. I would just wait and see if it is getting better, or getting worse.
Zone 7 A/B
Keep your words sweet. You never know when you may have to eat them.
Richard