sailfin plec

[black angel]

a friend of mine has this 12 inch plec and recently noticed these red swellings under the gills and they seem to be fluid filled. i am trying to get more info as to water conditions and anything else unusual but i would like to see if anyone here has had similar or knows what the problem is, thanks.

 

[black angel]

he was taken to the vet who did a scrape and found no parasites which is good and said it was probably scratched by the gravel and blistered. You can only see the red blisters when he breathes out so its in his gills. One side seems to have cleared up but the other gill is getting worse. Has anyone had this problem before?