Your fish goes about his daily life with two primary concerns - eating and avoiding being eaten. Propelled by these basic survival instincts, your fish employs all of his senses towards self-preservation and the propagation of the species.

At the same time, your fish is a living creature who can sense hunger, pain and threat, becoming aggressive when hungry and fighting for territory when challenged. Like any other pet, your fish can communicate with you if you know how to interpret his signals. To get a better grasp of the language your fish uses to communicate with you, it's important to understand how your fish functions and how he interacts with the environment.

Eyesight and Color Vision

Optimized to see at short distances, fish eyes have evolved to adapt to the environment in which they live: nocturnal fish have large eyes; muddy river dwellers have small eyes; and some cave fish are totally blind. In a brightly lit habitat, your aquarium fish will have average-sized eyes.

Tests using colored cards, stimulants and the fish's heartbeat have confirmed that all fish recognize color to some extent. As well, many strikingly colored fish species use their pigmentation to either ward off predators - Lionfish, for example - or to attract mates. Male Guppies, for instance, are markedly more colorful than females while some Blennies and the Thicklipped Gourami change color at spawning time.

Your fish cannot adjust quickly to varying light conditions, however, with some species needing up to an hour to adapt to new light levels. If you turn your aquarium's overhead light off or on, you should wait a few minutes until your fish have adjusted to the new lighting conditions before you feed them.

Good Vibrations

Sound travels nearly five times faster in water, and your fish is well equipped to detect it. Even without a middle and outer ear like other animals, fish can "hear" sound through the vibrations in the water. Your fish has a lateral line running along the sides of his body, porous and filled with water, that picks up disturbances in the water. For example, if there's a feeding frenzy going on somewhere in the tank, your fish will "hear" it through the water and rush to join the action.

Aside from the lateral line, your fish has an inner ear called an otiolith which functions very much like the human ear drum. And like the human inner ear, his "ears" help him maintain orientation and balance through cilia that send messages to the brain.

Because the tank walls and the water will reflect the sound waves, normal noise from your fish aquarium's surroundings, such as conversation in the room, is not loud enough to be picked up by your fish. However, if you tap the tank, stand or table holding the tank or if you scrape the lid against the sides, you will send very loud noises into the water, noises that could cause shock and a great deal of stress to your fish.

Sense of Touch

Surprisingly, fish have a highly developed sense of touch. Angelfish and Gourami use their pelvic fins not only as warning devices when coming out of a hiding place but also to grope and feel for food. Some varieties, like the Blue Gourami, have long whisker-like protrusions close to their pectoral fins which they use to both assert dominance during a territorial dispute and to help feel their way around. Catfish use their barbels to feel, dig through mud and gravel and taste food.

Taste Buds?

Yes, fish do have taste buds, even if they don't have tongues. Depending on the species of fish, these taste buds can be situated anywhere on the body. Catfish have taste buds on their barbels - to detect the strongest taste of food. They circle until their barbels pick up the "scent" and then zero in on their prey.

Some fish have taste buds on the skin used to send the food message to the brain where it is interpreted and the fish swerves towards the food. In species such as Goldfish where the taste buds are in the mouth, sensing is via the vagal lobe, the most highly developed part of the brain in fish. When your fish "tastes" something that is inedible, he'll immediately expel it.

Fish Can Smell, Too?

In fish, "smelling" is linked to tasting, and it is often difficult to distinguish between the two. A fish's scent and sense of smell, in effect, serve as a means of communication within groups of fishes. Certain "odors" are emitted by fish into the water to denote their rank and position within the group, and males are aroused by the scent that a female fish will give off to indicate that she is ready to mate.

Communicating with You

Most of the time, your fish's behavior can alert you to a problem in your aquarium. For example, aggressive behavior or attacking plants by a normally peaceful fish may be a sign of hunger or of stress. Some fish become territorial as they reach adulthood, requiring you to make the appropriate changes in your aquarium.

Some of the larger aquarium species like Oscars, Pacus, Triggerfish and Groupers can be hand tamed, and may even recognize you when you enter the room. And the most evident manner by which fish communicate is when the hungry ones learn to follow you, or your hand, as you approach the tank to feed them.

Intelligence in your fish and the extent of his ability to communicate with you is a reaction to the stimulants within his limited environment. Therefore, if you wish to maintain a healthy and happy aquarium, watch your fish's natural behavior and interpret it on his level. It's as simple as that.