"Blinking"

[Fish_lover101]

So one of my goldfish I've had for about half a year is/was doing fine but I've noticed a thing he does.. it's like he's blinking.. and yes I know and understand that fish don't blink but it's like blinking, does anyone know why fish do this? I've had a look on the internet and I can't find anything.

Tank size 36 litre.. Nitrite and ammonia are 0. Ph level is 7.5 and the temperature is 23 Celsius

 

[Autumnsky]

What I read was that they can roll their eyes back in a cleaning method but don't have eye lids.