Koi in pond @ botannical gardens

[BettaMomma]

Okay, so...
I have no goldfish, and know nothing about koi. So I thought I'd ask you experts if there's something "fishy" here with what I saw...

Yesterday we were at an indoor botannical garden and they had some GORGEOUS koi in a pond in the arboretum.
Something odd that I noticed, however, is that they had an aeration disk at the bottom of the tank, which had airline tubing leading to it across the pond floor. The fish were fascinated with the airline tubing, and at least 2 of them would go down to the bottom of the pond and swim sideways across the tubing, rubbing their entire side along the tubing. I also noticed that there were missing scales on each side of the fish that were doing this.

Now, I do have bettas and when they scratch it means there's a problem.
Is that the same story w/koi? Or are they just completely fine and just doing something they're known for? I felt like telling someone yesterday but there wasn't anyone around to tell. And I really didn't know if this is something they just do normally anyway.

thanks!

 

[bribones]

i found years ago that when i had the 12" airstone in my tank the fish used to love swimming across the top of it nothing wrong with the fish they just enjoyed it ,even with the pond my fish love to swim under the water outlet of the filter might be there is a problem or maybe there just playing and the line has something about it that makes em wanna rub