What is the circle shape line on this rose red?

[mikechen]

Hi,

Recently I found one of my friend's rose red has a circle shape line on its body. What is it? Thanks!13228

[Timbo]

its called the lateral line

[nacra99]

The lateral line is the fish's "Ear". It detects changes in water pressure from movement and low freq sound, analogous to how our ears detect changes in air pressure due to sound waves.

[aqua]

Look like it got sucked into the tube during water change.