in switzerland we used to use trouts but now we use daphnia because they use less space and are easier to reproduce in a lab setting. i used to work in QA for a water treatment facility and it is super facinating,(reply>), stfu and let Poland have its moment,(reply>), @John Dor they die.,(reply>), @John Dor I guess at a minimum, when the water quality drops below a certain level they swim to the top of the water and float upside down.,(reply>), The water fleas are monitored by cameras. If the swimming pattern changes the alarm goes off I believe. Also done In Germany.,(reply>), @John Dor they die