Spraying cyanide near coral reefs teeming with tropical creatures can quickly and cheaply stun ornamental fish that can then be scooped up and sold around the world. The practice supplies pet stores but often leaves behind damaged coral and dead fish exposed to too much of the toxin. Countries where aquarium fish are collected have outlawed the method decades ago, but catching perpetrators is difficult. Now researchers are developing a handheld device for detecting cyanide fishing that could help clamp down on the destructive practice.