The ability to adapt, thrive and communicate with and within the environment that any given species inhabits is paramount to survival. This is true of all life on earth but holds a special grip on aquatic life, which has had to evolve in – and adapt to – an environment where sound, light and scent travel very differently than they do in a terrestrial environment.
15 Minute Read.
When discussing any given form of aquatic communication, it is not simply referring to the common term which might indicate that two people are talking.
Instead, “communication” defines the visual, auditory and pheromonal cues which allow fish to directly or indirectly advertise or conceal their presence, as well as pass along information.
Not only is aquatic communication an interesting subject in itself, but understanding it can give those of us keeping fish in captivity, a better insight into setting up aquariums, dealing with water quality and minimising stress.
One key adaption that has helped fish thrive in aquatic environments is their well-developed sense of smell. A well-developed sense of smell aids in predator avoidance, individual recognition and reproductive behaviour.
In the almost boundless multitude of fish species, some have inevitably evolved with poor eyesight; for these fish, chemical signals are especially important. In Chemical Communication; Pheromones can allow fish to recognise the gender and sexual condition of other fish.
This is particularly useful for fish that have evolved in fast, turbid water or those that inhabit water bodies with little light .
For example, certain species of fish, such as goldfish (Carassius auratus), rely on pre-ovulationary pheromones to recognise members of the opposite sex with which they can mate.
In 1956 W. Tavolga discovered that among frillfin gobies (Bathygobius soporator), males will exhibit courtship behaviour when in the presence of ovarian pheromones in the water – even when no females are present.
At the opposite end of the spectrum, many fish will avoid certain areas when the pheromones of a dominant individual are present. This is because pheromones can also help fish to recognise the group standing of the individual they are encountering based on the nature of the fish’s pheromones.
This means they can make an educated guess about whether to challenge the fish for standing or territory or to avoid the fish altogether.
Scents also warn fish about the presence of a predator and they can aid in preventing cannibalism of members of the same species. An attack upon a fellow species member would result in the release of fear scents known as ‘schreckstoff’ (German for scary stuff).
These scents encourage other fish of the same species to engage in predator avoidance behaviour. Such behaviour could take several forms depending on the species and habitat. The injured fish doesn’t intentionally release the chemical that makes up schreckstoff, as evolution wouldn’t favour genes which give of scents which can potentially inform predators that the individual is injured.
However, it is evidence of evolution favouring kin selection because the act of warning one’s siblings and cousins about danger helps protect one’s own genes.
The information that these examples give us as fishkeepers reveals new ways to structure our care for the fish we keep. For example, if a shoaling fish has died or injured itself, a water change, in addition to mitigating water pollution, will remove some of this schreckstoff.
This, in turn, will reduce the stress on the other fish, as well as lessen the chances of them falling victim to the same fate, as fish can be very susceptible to stress.
Another question that arises is: How safe and applicable are the shared rack systems you find in most fish stores? It stands to reason that if smaller fish can detect, from pheromone cues, the presence of a predator a few tanks away, the smaller fish would almost certainly be more stressed than if it were in an isolated system.
While this issue is almost unavoidable for large retailers, it does have implications for some individuals in the hobby.
Through common sense and shrewd deduction, it is possible to determine how pheromone cues affect you fish and, if necessary, how you can reduce this stress on them.
Sounds are produced by a range of fish species to attract mates, threaten rivals and to confound predators.
Of the many variations of auditory several stand out; Stimulation is the act of producing sound by rubbing together certain body parts. Some fish use the specialised spines of their pectoral fin to produce a squeaking sound by rubbing these against the pectoral girdle; this method is often favoured by catfish.
One of the most evolved methods of communication amongst fish is the vibrating of the swim bladder, which creates buzzing and whistle-like sounds.
The swim bladders of these fish tend to be attached to muscles that vibrate the swim bladder to obtain control over the sound. Now the function of sound has two primary functions for fish.
One is defensive communication and the other is reproductive communication.
In Astatotilapia burtoni, an African cichlid endemic to Lake Tanganyika, dominant males will call to attract females for breeding purposes. Larger males will produce louder calls, while subordinate males will use the volume of another male’s call to determine whether they can take over their territory.
The louder the male’s call, the less likely his territory will be attacked.
Similar to phenomenal communication, auditory communication allows fish to advertise their presence to rivals and mates alike.
While this does not have many uses in the aquarium, it can remind us that some species that rely heavily on auditory communication may have issues with their group dynamics if aquarium equipment is vibrating against tank sides or being unusually noisy.
The most prolific form of fish communication is, by far, visual communication.
Colouration and behavioural movements are used to communicate with interspecific and intraspecific fish species.
Fish can use pigments to change their colouration which in turn allows them to conceal themselves, advertise their presence and attract mates.
When a fish changes colour or patterning, Pigments are released into their skin by Chromatophores which are like a river system throughout the fishes body, made up of a central area out of which emerge many ‘branches’.
These branches can be filled or emptied of pigment depending on the environment and when the branches are filled, the pigment affects the appearance of the fish’s skin.
These chromatophores are arranged in several layers, if the top layer is black, then when the top layer spreads throughout the branches in the cells they will appear black, yet when if the pigment black is concentrated in the centre of the cells the branches will become transparent which will allow the colour cells below them to become visible, these might for example be red.
This would mean that the fish has changed its colour from black to red.
There are three pigments which are Erythrin (Red), Melanin (Black), and Xanthin (Yellow); more than one pigment can be present in the Chromatophores and this mixing can lead to a variety of colours
These range of colours and the ability to change quickly has evolved to allow fish to communicate between members of their own species, advertise their threat to potential attackers or to conceal themselves in the presence of predators.
All useful tools in an underwater world filled with hazards and challenges. The varied colouration in fish is used to communicate between members of the fish’s own species but in drawing attention, unwanted attention from predators. Most fish have evolved to achieve a balance, benefitting from visual communication without attracting predators.
To serve this purpose, several adaptations have evolved in fish. Below are a few examples.
Eye spots are false eyes, usually on the caudal peduncle, which direct predators to the fish’s tail end. This gives the prey fish a few vital seconds to escape. Eye spots are often found in cichlids and
Characidae along with eye ornamentation, which occurs when the eyes have evolved to be more inconspicuous in the surrounding skin. In some cases, the fish’s eyes and the skin that surrounds the eyes are similar colours. In other cases, the fish may have similar-sized spots in the area of the eyes to create visual confusion. Symphysodon discus has evolved to possess lines on its body that match the eyes.
Lateral stripes which are found primarily in schooling fish. These are lines that run down the middle and side of the fish; they help schools stay together and properly adjust in terms of their orientation towards each other.
Predator confusion comes about when schools use their lateral stripes to create an apparent fusion between prey individuals. Predators then find it difficult to pick one individual out from among the school.
“If a fish can disrupt its outline, it is less likely to be discovered by predators.”
In the 1960’s Konrad Lorenz, the father of ethology, coined the phrase ‘poster colours’.
However, he wrongly assumed that these very bright and ‘billboard-like’ poster colours, are purely for advertising territory ownership.
More recently, poster colours have also been considered means of advertising presence, sex and species identity, amongst other things.
Bright and complex colourations are connected with a variety of functions, including: maintaining contact whilst foraging; serving as camouflage in a colourful coral reef; making a bright statement to predators about the presence of poison or spines; and indicating status.
Another visual aid is counter shading; if a fish can disrupt its outline, it is less likely to be discovered by predators.
To achieve this, many fish have darker dorsal/upper bodies so that fish above them cannot detect their presence against the dark of the waters below. In addition, lighter undersides ensure that predators cannot notice them against the light of the sky above.
Bottom dwellers also regularly utilise pigments to disrupt the image of their outlines, allowing them to blend with their surroundings.
This is known as disruptive colouration.
When we observe these traits and adaptations in our own aquarium fish, we can adapt the aquarium to suit these adaptations.
For example, angelfish, with their dark vertical stripes, will feel more comfortable in an aquarium with tall, vertical plants.
This is because their natural environments often include tall, vertical structures and plants, which they use for cover, camouflage and ambushing prey.
Also, the anatomical features of shoaling fish indicate why such fish should be kept in large groups. For example, penguin tetras have lateral stripes which help them maintain their orientation to each other.
These examples not only reveal how we can change, create and manage our aquariums with our fishes’ anatomy in mind; they also help with stocking choices. For example, male Siamese fighting fish (Betta splendid) can only live alone.
Keeping more than one male will result in fights and stress, and often lead to the death of one fish.
These fish recognise other males through their long, flowing fins and poster colours.
As fishkeepers, we can see that if male bettas recognise other males through these traits, other aquarium fish such as guppies (Poecillia reticulata) and sword tails (Xiphophorus hellerii) may be unsuitable tank mates due to their similarities in terms of long, flowing fins and bold colouration.