Visual communication of fish
Animals have evolved a great number of mechanisms for communicating. The signals emitted carry information on reproductive readiness, species affiliation, position in the herd, and threat. They are also used to deter, threaten as well as express peaceful intentions. These skills are indispensable when it comes to getting along within the herd, with the owner of a neighboring revue, with a partner, with offspring. Fish communication occurs through colors, body posture, sounds, electrical waves, chemical compounds including pheromones. Some of these signals are constant (species affiliation) but others are emitted periodically e.g. mating colors, colors indicating nervousness, pheromones during the breeding season, threatening behavior, etc. Visual communication of fish is a very important way for this group of animals to communicate. Also read about the fascinating sound communication of fish.
Visual communication and fish colors
The visual organ plays an important role in receiving information emitted by other fish. With its help, colors as well as body posture are recorded. Colors signal mood, sexual maturity, readiness to spawn and position in the herd. When interpreting fish coloration, there are always many factors to consider. Ignorance of facts about the habitat, behavior of a species can easily mislead the observer. Furthermore, the way we perceive fish colors is quite different from how the fish see themselves.
Very often fish colors are a compromise between the need to communicate and the need to avoid danger. The former requires the colors to be bright, contrasting and striking, while the latter needs them to blend in with the surrounding environment. But that’s not all. Whether or not colors and patterns are visible depends on the color of the environment, the clarity of the water, the lighting, and what visual abilities the receiver of the signal has. It should also not be forgotten that fish can more or less change their coloration.
Colors and patterns of fish during spawning
The intense colors of the males during courtship are intended to encourage females to spawn. During this period, the colors and patterns on the male’s body carry information for the female about his readiness to spawn, his condition and species affiliation. A great number of laboratory studies and field observations prove that color-selective mating in the cichlid world plays an important role in species formation or maintenance of color forms. Because of their great affinity, and thus similarity, cichlids from lakes Victoria, Malawi and Tanganyika are very eagerly studied in this respect. Scientists are interested in how, in this colorful mix of similar species, females make their choice of the right male. A great deal of observation indicates that color (as you will read below perhaps scent as well) is the main deciding factor.
This conclusion was also reached by researchers observing for three years several Tropheus moori color forms from different locations, which accidentally ended up together in a small bay of Lake Tanganyika (this coincidence is, of course, an ill-considered human action). Based on genetic studies, scientists have shown that mating between color varieties has not generally occurred. The color of the males was a clear information that determined the choice of females. This research is interesting because it was conducted under natural conditions.
Beautiful colors are a sign of health
Intense colors of the male are a signal for the female that it is a healthy individual and in good shape. Cheating is not an option, as the cost of maintaining attractive coloration is high, sick fish are unable to expend the necessary amount of energy. Three-spined stickleback females choose the reddest male among the fish they encounter. A pale color is a signal that the male is infested with parasites. Red is a color often used by males to attract female partners. This is an interesting example of compromise, because from a close distance the red color is clearly visible, so it fulfils its role during courtship. At longer distances, especially when seen from the side and in shaded water, red is perceived as a dark colur, making it easier to hide from a predator. This is due to the absorption of red radiation by water.
Colors warn and inform of intentions
One of the functions of the bright, poster-like colors and contrasting patterns so common in saltwater is to inform the environment that the bearer of these colors is poisonous. Of course, they take advantage of this by various copycats to send a false message about their lack of fitness, despite generally being as edible as possible. Colors therefore allow the transmission of information within species and between different species. An interesting example of interspecies communication is represented by the bluestreak cleaner wrasse, which cleans the flesh of sharks, shrews, etc., of external parasites. In order not to become a snack to its service recipients it sends the information that it is a desirable species and it does not “pay” to eat it. This signal is the characteristic coloration and type of dance it performs before its host.
Colors used by the fraudsters
The colouring of the bluestreak cleaner wrasse was used by another, not so friendly species – Aspidontus taeniatus, which, pretending to be a cleaner, swims close to the fish and bites off pieces of their fins and skin.
This species has mastered both the wrasse’s dance and developed the colors typical of that species, even taking into account the color differences of local varieties. This is an example of mimesis – the resemblance of one species to another or to the surrounding environment. The goals may be different – the desire to hide from a predator or prey to make it easier to catch, to pretend to be a species capable of defending itself (mimicry) or just to impersonate a harmless species.
Fish colors as part of camouflage
Neutral colors of juveniles not only allow them to hide, but they also inform other specimens of the same species that they are sexually immature and do not pose any competition. Many times it can be observed how the males of some species in the aquarium do not adopt the colors typical of sexually mature individuals. They camouflage themselves, they send a message to the alpha individual that they are not competition. Another thing is that pretending to be sexually immature males, or even females, they can spawn under the dominant individual’s side.
The fish’s body posture is also information
Posture also plays an important role in visual communication. The fish may assume an imposing posture, threatening the intruder, or deterring the predator. Sometimes it is enough just to open up the gill lids a bit or straighten fins. However, probably the most spectacular posture can be adopted by Tetraodontiformes, which in the moment of danger inflate, increasing the size of their body and taking the shape of a ball.
Visual communication of fish
Particular ways of visual communication have been developed by schooling fish. Living in a school increases safety, but also requires members to have strong communication skills. Communication in the school is by optical and most likely chemical signals. Horse mackerel is a schooling fish. Its silvery coloration and key ‘glowing’ points (dots at the base of the caudal fin, main lateral line, dorsal lateral line, points at the base of the pectoral fins and in front of the eye) are important tools for communication within the school.
Bright spots at the base of the fin convey information about the fish’s activity. The glowing lateral line allows the fish in the school to maintain their position, as the fish can see the maneuvers of other animals in the herd from the line. The dorsal line is a source of information which side the observed fish is facing. In addition, depending on the angle of the light and the angle of observation of the fish, different parts of the body shimmer in different colors due to the two layers of guanine plates. These colorful reflections are also most likely used in communication.
Without a doubt, it can be said that the visual communication of fish makes it possible to convey a great deal of information in an extremely short time. It seems that fish use this method of communication very readily. But what if the water is murky and the sense of sight becomes useless?
Literature
- Moyle P. i inni (2004), Fishes an introduction to ichthyology, Prentice Hall.
- Rowe D.M., Denton E.J. (1997), The physical basis for reflective communication between fish, with special references to the horse mackerel, Trachurus trachurus, Phil. Trans. R.Soc. Lond.
- Salzburger W. i inni (2006), Colour-assortative mating among populations of Tropheus moorii, a cichlid fish from Lake Tanganyika, East Africa, Proc.R.Soc. B, 273, 257-266.
She studied environmental protection (specializing in surface water protection) at the Agricultural University of Wrocław (now the University of Life Sciences), where she later obtained her PhD at the Faculty of Biology and Animal Husbandry.
Her research focuses on the effects of diet, supplementation, and natural additives on the health, condition, and reproduction of aquarium fish.
In her free time, she cares for her fish and cats, tends to plants, enjoys hiking, and stays active through sports.
- Let’s find out how phosphorus affects fish in an aquarium. - March 9, 2026
- Phosphorus transformations in water? - February 23, 2026
- Phosphorus in the aquarium – its role, forms, and measurement - December 4, 2025
