The wide range and variability of aquatic habitats colonized by the world's fish has given rise to an incredible array of sensory organs, structures, and adaptations. Different kinds of fish possess varied sensory strengths due to adaptations that have occurred over years of evolution. Each type of fish has sensory traits that allow it to best interact with and succeed within its environment.

Fish lack external ear openings, so you tend not to think of them as creatures that can hear sounds. Most species, however, have well-developed inner ears. These structures are very effective at sensing the waterborne pressure changes that accompany sound waves.

In a further refinement of the inner ear, some species of fish possess a connection between this organ and the swim bladder. Gas in the swim bladder improves the fish's hearing acuity, because gas is very sensitive to the vibrations caused by sound waves. This results in an ability to decipher a wider range of frequencies and tones. It is believed that fish that possess advanced hearing abilities communicate extensively with one another using sound.

The lateral line is a unique system of neuromasts, which are sensory organs that detect water disturbances caused by the movements of other animals or by the flow of water over objects. These organs are mainly comprised of jellylike substances called cupula that rest on sensory cells. The neuromasts are housed within lateral line canals that run along both sides of the bodies of most fish, although in some species, the organs are scattered about the surface of the head and body. The functioning of the lateral line system appears to be particularly effective and well developed in sightless species such as the blind cavefish.

Many fish make good use of the fact that water is an excellent conductor of electricity. Electrical receptors in fish generally exist in the form of modified lateral line organs. These unique structures sense the electric currents generated by the muscular action of swimming fish or by the heartbeats of nearby animals. This ability seems to be particularly well developed among the sharks. It also appears that some fish can detect the earth's electromagnetic field and may use such to orient themselves during lengthy migrations.

Some fish can also produce electricity through the use of specialized cells in the swimming muscles. Most fish that can generate electricity, such as the knife fish, produce fairly weak currents that are used for communication and navigation. Several species, however, most notably the electric eel (actually a type of knife fish), the electric ray, and electric catfish, can produce currents of several hundred volts in strength, enabling them to stun prey and discourage would-be predators.