Hi Ava, I would'nt worry too much but I think its a thing best done in moderation.
My brother and I (both grey haired grown up kids) was looking in awe at some hug Koi at an aquatic centre, I decided to put my hand in the water and these monsters imediately started sucking my fingers, then some real kids came along and thought it looked like fun and started doing it too, but a little less restrained, anyway we wandered off for a further look around and walked back by the koi again 5 minutes later and we noticed the staff had rolled a net over the tank. I noted the fish had a price tag which was more than what I paid for my car, so I think covering the tank was a pretty wise move!