When we go to sleep at night, we close our eyes to stop any errant light from disturbing our slumber. But the larvae of zebrafish go one further. They shut down their eyes entirely at night, becoming temporarily blind. Their vision only returns when daylight does. Energy is precious to the baby fish and eyes are gas-guzzling appliances, even when they’re set to standby. It makes sense to just shut them off instead.

Read more: Pocket Science –zebrafish babies go blind at night