The senses of fish

Fish are well adapted to their aquatic environment. In addition to the five senses known to all animals, the lateral line helps them find their food and detect danger, even when they are unable to use their sense of sight.

The lateral line. Nerves on each side of the fish perceive the vibrations of the water, which allows it to determine the size, speed, action, and direction of submerged organisms and objects. Small fish use this sense to escape predators. Pike, zander, black bass, trout, and other predators rely on their lateral line when chasing bait fish. The lateral line of the gregarious fish is also of great help when moving in compact and homogeneous groups.

The view

As in humans, fish perceive brightness and color thanks to the cones and rods of the retina of their eyes.The rods are sensitive to the intensity of light, while the cones identify the colors. Several species of deep-water fish, such as black bass, have excellent color perception. In good light conditions, as they are found near the surface of the water, these species can detect most of the colours perceptible to the human eye. However, many fish cannot perceive the full range of colors. Zander, for example, does not perceive orange and green, the other colors appearing to him as shades of gray.

Water acts as a filter on the colors, so fish living in deep water cannot distinguish all the colors perceptible near the surface. Red is the first color to disappear in depth, followed by yellow and blue. Because they can only see a very limited number of colours, depth fish are more sensitive to light reflections from other fish, predators or prey. However, the eyes of some species are ultrasensitive to some colors, even in deep water. For example, green and especially orange can be perceived by zander at depths to which the human eye would be unable to distinguish any color.

Even the majority of sports species have a color vision, the shape and hue of a lure are often less important than its shine and are action. This may explain the effectiveness of red and white spoons and purple plastic worms, even if these colors are not naturally present in the fish environment. However, in some cases, the lure must mimic exactly the shape of the fish food. A typical example is a trout feeding on a particular insect species.

How far fish can see in the water depends on its clarity. Some species see more than 30 meters in clear water, but in general, the viewing distance of species living in lakes is between 3 and 6 meters.

Pisces sees the outside world through a "window" on the surface of the water. The diameter of this window is approximately double the holding depth of the fish. In other words, a fish standing 1.5 meters below the surface of the water sees through a window 3 meters in diameter. Because light rays are diffracted when they enter under water, fish can see outside objects that are far from their window. Around the window lies the «mirror», a large portion of surface through which the fish cannot see because the image of submerged objects is reflected by the lower plane of the surface film.

The ear

Fish have a very developed sense of hearing, which is explained by the fact that water is better conductor of sounds than air. Fish don’t have ears, but they hear the sounds directly through the bones of their skull. However, the response to perceived sounds varies greatly from species to species. Thus, a single light step on the bank can frighten a trout while moderate agitation on the dock does not disturb the poles, it even happens that it attracts them.

The taste

Most fish have some perception of taste, but few species rely primarily on its senses to search and identify their food. Catfish are an exception: their skin and, more specifically, their barbels are equipped with sensory cells that allow them to taste the food before swallowing it.

Smell

Fish can detect odors with great sensitivity. Salmon returning to spawn in fresh water detect their native river thanks to the olfactory molecules found there. Some species can detect substances in concentrations as low as a few parts per billion, which is about the equivalent of a drop of substance in a lake 10 square kilometers in area and 6 meters deep.

The olfactory sense of the fish also warns of the proximity of predators and prey. When caught by a predator, the catfish emits a chemical through its skin that warns its congeners of danger. For example, salmonids in spawning runs go downstream if the skin of a man or bear comes into contact with the upstream water. During a laboratory study, it was enough to add a little water from a pike aquarium to that containing perch to terrorize them. Predators, such as pike and zander, can detect the smell of live or dead bait fish. The sounds produced by a lure can attract fish, especially in troubled waters. Some lures have an internal sound chamber containing balls that collide.