Sick fish?

[seaweeds]

I just added this fish to aquarium 2 day ago and now noticed that it has a reddish line behind the fin. Is this normal or is it a parasite?

 

[Colin_T]

Which fin, where is the red line?

I can't see anything in those pictures. Try taking pictures of the fish in the tank and check them on your computer. Find one that clearly shows the issue and post that picture here.