Redness On Black Skirt Tetra

[rachh004]

I just added 2 small black skirt tetra into my tank. I already had 2 grown ones in there. The little ones are chasing the big ones (i think they are actually just hanging out with them and the big ones do not like them). but the little ones have this red line in the middle starting from the side fin to their back fin, on both sides. I don't know what it is. I was thinking it could be from stress. But i don't want it to be serious. But could it be from chasing the other ones- like bumping into them?

 

[Hawkins]

if it gets worse then you should start worrying.

dont panic right now though

 

[rachh004]

They are ok now. I don't know what it was but it seems to have gone away. The reason I was worrying was because my platy was bothering one of my adult tetras and I didnt want him bothering the little ones.