Crayfish cannot tolerate bright light.

This is one of the reasons why it can be found from 20 meters deep down to 800 meters. In fact, its entire circadian rhythm is tailored to the light. Crayfish that live in shallow water are most active at night, and those that live a little deeper are active at dusk and dawn. Those that live the deepest often take advantage of the little light during the day to find food. The sea crayfish is omnivorous, so its diet consists of everything from mollusks, barnacles and crustaceans to carrion.