Click on the fish in 2d mode (not sure if this is what you are actually asking about).

Thank you very much for your answer, but I meant something else: If I have some fish in the aquarium and just want to look at them - is there a way to focus the "camera" on a specific fish and have the camera follow that specific fish? That would be nice.

This seems to be the "auto camera" in 2d mode I was referring to?

Thank you for your answer. I tried out the 2d mode again and i could follow a certain fish, but not all the time - but that doesn't matter. My question is answered. Many, many thanx to you and best wishes :-)