What are these lines?!

I left for the weekend and when I came back both my male mollies had 5 or so grayish lines behind their fin? Does anyone know anything? Is this a problem?
Sorry couldn't get them to stay still for a pic but if you really need one just say so.

 

I've never seen or heard of this before can you try to get a picture?

 

sorry there hard to see but there just little gray dashes sort of like shark gills

They might actually be fine my fish are going through "puberty" like my males fin got super big over night.

 

They look normal to me I wouldnt worry about it.Are they new they might just be getting used to the tank and starting to color up.

 

Yup that sounds right

They are new and getting more active too!

 

Then they are ok,they are just getting their color back.

 

Thank you!

 

Your welcome.