Yes, that was very jarring. I didn't bother reading the intro text that said the other fish are other people on the site, so I just thought this was janky crap. The creator shouldn't assume people read anything. I see a button that says "Enter", I click - I'm not reading anything else. So it's going to cause a lot of confusion when I arrive in a pond filled with way too many fish for a zen-like experience, and even more annoyance at the constant flickering in and out.

Thank you for the feedback! It’s definitely on my project task list.

So far the options I thought of were to fade or scale the koi as they enter or leave the pond. I will try to see what will work visually here.