Visual communication is important to most fish. Body movements, postures, colors, color patterns and light are the primary means of visual communication. Sound is also used for communication. Sounds are produced by grinding teeth, rubbing body parts together and with the swim bladder, an air sac inside the body used to regulate buoyancy. Drum, croakers and toadfish get their names from the sounds they produce with their swim bladders.
Fish also communicate by producing chemicals called pheromones that other fish can smell.
A few fish that live in very muddy water where visual communication is impossible use electricity to communicate. They pick parasites from other fish. Cleaning fish, such as wrasses, are brightly colored or patterned. They establish cleaning stations that other fish approach in order to be cleaned. Look for fish in a funny position or holding their fins out.