Fisherman often use potassium cyanide and other poisons to stun and capture valuable reef fish. Divers squirt a cyanide solution from bottles directly onto fish resting on corals, killing the corals and stunning the fish. The fish often escape into crevices and the fishermen have to break apart the coral to get to their paralyzed prey. With this technique not only the fish are poisoned, but also the coral polyps and other creatures in the area. Places where cyanide was spread will first form black slime, then they will just become dead coral rock.
This method is used to catch tropical fish for aquariums or to capture valuable fish such as the Napoleon wrasse or groupers for "live fish" restaurants. Of course not all fish survive, it is said that 40% of exotic fish die before they reach the aquarium. Exports of these animals are often formally banned but nether the less done everywhere. According to Interpol the illegal trade in wildlife and wildlife products ranks second only to drugs in terms of financial rewards.