Fish that generate electric fields to navigate, fight and attract mates are equipped with a dimmer switch of sorts that can turn down their signals to save energy, a new study finds.

Electric fish, such as some sharks and eels, emit weak electrical signals from a battery-like organ in their tails. The fish studied, called Sternopygus macrurus, are active at night and must avoid predators, such as catfish, that can sense their electric field.

Generating such impulses can be energetically costly.