I had this exact question, and the researchers said it was a serious consideration. Turns out the critters at this scale move quite slowly and so does the wheel

I had this exact question, and the researchers said it was a serious consideration. Turns out the critters at this scale move quite slowly and so does the wheel. There's some effect certainly but it's small enough that they can track a single organism for quite a long time. It wouldn't work in other circumstances or scales for sure. I wrote it up here, in case anyone would like to read about it in article form: https://techcrunch.com/2020/08/19/this-looping-aquatic-treadmill-lets-tiny-ocean-creatures-swim-forever-under-the-microscope/ https://techcrunch.com/2020/08/19/this-looping-aquatic-tread...