Fishes might not talk to each other like we do. But studies show that they communicate with sounds, chemicals, motions, light, electrical impulses, etc. Though fish can communicate in variety of ways, sound is the most effective way in aquatic environments.
Communication through sound
Fishes don't have specialized organs like larynx and vocal cords to produce sound. So, they make sound by striking or gnashing their teeth or by rubbing their pectoral fins against other objects. In some fish the sound is produced by the swim bladder. The sonic muscle which is attached to the swim bladder contracts and relaxes sequentially making the bladder vibrate which in turn produces sound. Sound travels faster than it does in air because water particles are more densely packed than that of air. Besides this the energy of the sound waves is quickly lost along the way when travel through air. And sound retains its energy longer when travel through water because water particles conduct sound waves better when compared to air. For example the sound of a humpback whale can travel thousands of miles.
Communication through Pheromones
Like some creatures such as ants, fishes also use pheromones to communicate. Chemicals used to communicate within a single species are called 'pheromones'. Generally pheromones are secreted by females and are efficiently received by males. Such as in Zebrafish the pheromones are released by females to attract the males.
Communication with color
Some fishes can change their body color. The most obvious reason to change their body color is to hide from predators. Many fish species can darken or brighten their hues to communicate emotions, to frighten predators, etc.
Communication through light
In the deepest parts of the oceans, fish like Anglerfish emit light because it is dark and to attract the prey. You may have seen this fish in the popular Finding Nemo Pixar movie. This emission of light by living organisms is called Bioluminescence. Bioluminescence helps in recognition of different and communication with other creatures in the dark.
Communication through electrical impulses
Some fish like electric eels have electrical organs that enable them to transmit electrical impulses, warning the predators to stay away.
And finally, just as humans talk in different ways, fish also talk in many different ways.