Sound communication of fish
Contrary to popular belief that fish have no voice, scientists have found that many species communicate with each other using sound waves. Sound communication of fish is quite popular. However, only a few of the sounds made by fish are audible to humans. Ichthyologists distinguish sounds which are used to call out other fish, for instance during spawning (Pomacentridae, sunfish, toadfish, elephantfish, catfish), to scare away other fish (useful in all kinds of fights) or to express emotions (e.g. fear).
Based on current knowledge, it is believed that fish sound communication is an important information carrier. It has also been found that the sounds produced by related fish species, e.g. sunfish, Pomacentridae, elephantfish, cods, and gouramis, differ in the “pattern” of sounds made. Elephantfish and sunfish have been proved to distinguish sounds made by individuals of the same species from the sounds made by the related species, especially on the basis of impulse rate. Elephantfish of the genus Pollimyrus are able to distinguish crackles repeated at intervals of less than 1 millisecond.
How fish generate sounds
Fish have developed a wide variety of mechanisms to generate sounds. In general, there are three ways of producing sound: the rubbing of hard structures against each other – this type of sound is known as stridulation (this mechanism is also used by insects, e.g. the grasshopper), vibration of the swim bladder, and sounds produced accidentally during some activity.
Stridulation
Stridulation generates low frequency sounds, sometimes inaudible to the human ear. Without a doubt, it is the most commonly used mechanism for intentional sound production. Perhaps this has to do with the fact that it requires very little modification within the body of the fish. Stridulatory sounds can be produced, for example, by rubbing the pharyngeal teeth (cichlids) or maxillary (triggerfish) teeth against one another. Rubbing special roughened surfaces of the fin rays, usually pectoral, against the articular acetabulum in which the base of the rays (catfish) lies, is equally popular. The resulting sounds are often amplified by the swim bladder, which is connected by muscles to the structure that produces the sounds. Stridulation is also used by cottids to make the bones of the shoulder girdle vibrate. A popular pygmy gourami squirms by setting the enlarged pectoral fin muscles in motion.
Vibration of the swim bladder
With the help of the swim bladder, fish make low, buzzing, burbling and other sounds. This mechanism is used by representatives of characids, sea robins, elephantfish, catfish and Batrachoididae known as toadfish because the sounds they make resemble the croaking of meagres, also known as stone basses. Bladder vibration is caused by special muscle groups that have the ability to shorten at a very high frequency. They may be connected directly to the bladder or indirectly through a system of, for example, ankles or other structures.
Very often, making a sound using this mechanism involves significant changes in the structure of the swim bladder. The noisiest fish are those whose bladder vibration is caused by the internal muscles of the swim bladder, e.g. toadfish, sea robins and flying gournards (from Scorpaeniformes family). Very noisy fish also include stone basses (Sciaenidae), called “drums”. They create sounds by rapid contractions of muscles located near the swim bladder.
Perception of sounds by fish
Among fish studied to date, catfish have the greatest diversity in the mechanisms used to produce sounds, using both the swim bladder (a number of different modifications) and the stridulation. In these “talkative” fish, scientists studied not only organs used to create sound but also those used to perceive sound. This is an interesting issue because many catfish have had a reduction of the swim bladder as an adaptation to a benthic lifestyle, and it is this organ that is involved in the hearing process. Eleven fish species from 8 families were included in the study, having been previously divided into two groups:
- Fish with a large, single, free bladder and 1-4 auditory ossicles: Ariopsis seemanni, Batrochoglanis raninus, Malapterurus beninensis, Pemelodella sp., Synodontis shoutendeni, Trachelyopterichthys taeniatus.
- Fish with a small, double bladder surrounded by bones and 1-2 auditory ossicles: Ancistrus ranunculus, Corydoras sodalis, Dianema urostriata, Hemiodontichthys acipenserinus, Hypoptoma thoractum.
In summary, fish in the first group with a large swim bladder appeared to hear better. Species that had a greater number of auditory ossicles (3-4) in the Weberian apparatus were able to perceive higher frequency sounds. But yet another interesting conclusion was drawn from this study. It turned out that the fact that benthic fish did not fully reduce the swim bladder is most likely related to its function in the process of acoustic communication.
Differentiating sounds by fish
Of course, the sounds made by fish cannot compare to those of land animals in terms of complexity. These are not sophisticated or complex “utterances,” but nevertheless some genre- and situation-specific features can be identified, e.g., sound duration, sound wave frequency, repetition rate, etc. Fish are able to recognize sounds emitted by the representatives of their own species. Based on this, females can make their choice of a suitable mate. The different characteristics of the sound produced by closely related fish living in a given territory can act as an effective reproductive barrier, preventing species from interbreeding. As you can see, sound is important in fish communication.
It has been found that the loudest sounds are emitted by fish when they are defending their territory or engaging in other aggressive behaviors. Spawning can also be loud. Males of Porichthys notatus are particularly loud during the breeding season.
Different fish populations – different sounds
Aquarists are familiar with the concept of geographic varieties of fish, which is most often associated with differences in coloration of individuals from populations living in distant territories. It turns out that the differences may also apply to the produced sounds. The marine fish Opsanus tau produces different sounds in distant populations. However, the scientists pointed out that this species did not have a pelagic stage, and thus the larvae were not freely carried by the water to other regions. The species with a pelagic stage, Dascyllus albisella, even in populations 1000 km away, produced a similar sound pattern. Scientists attribute this fact to the lack of genetic differences between the observed populations of this species, which they link to larvae moving around during the pelagic phase.
Also, many Pomacentridae fish, including the popular orange clownfish, show no significant genetic differences even in populations 3000 km apart. Orange clownfish produce sounds during courtship and to deter competitors from the occupied polyp. The two groups of sounds are significantly different. Amphiprion akallopisos forms groups consisting of reproductive females and males and non-reproductive males. The territory is defended by the female and it is she who makes the deterrent signals. Despite the lack of clear genetic variabilities, differences in the sounds made have been found in this species depending on the occurrence of the population. Scientists, however, have not found a clear explanation. Perhaps these differences are due to adaptation to the background sounds in a given territory or to biotic factors of a given environment.
Structures used to perceive sounds
As the organs for making sounds developed, so did the ability to receive such signals. The most distinctive is Weberian apparatus, which connects the swim bladder to the membranous labyrinth (the actual organ of hearing). The system of ossicles that forms Weberian apparatus transmits the vibrations of the swim bladder to the inner ear. This structure is found in fishes classified in the superorder Ostariophysi which includes about 8000 fishes. Elephantfish can hear due to the presence of a auditory bulla in their skull and labyrinth fish use the labyrinth, which is an air chamber located above the gills, for this purpose. Its main functions include breathing air, but in addition to that it lies adjacent to the middle ear, so it easily transmits amplified sounds.
Sound communication of fish – interesting facts
Scientists who study fish sounds often discover very interesting facts, e.g. goldfish and two-spotted gurami do not make sounds, but they are among the fish with high sensitivity to sound. This allows them to perceive vibrations in the range of 200 – 2000 Hz and 300 – 2000 Hz respectively. Bad hearing fish are found among both sound-producing (Corydoras paleatus) and “silent” (Eigenmannia virescens) fish.
It should be noted that the ability to generate sounds and sound communication is not common to all fish of a given taxon. Although this ability is found in ostariophysians and labyrinth fishes, not all representatives of these taxa can do it. Also, “mute” fish are found among elephantfish, cods, and Pomacentridae fish, although these groups of fish are known for their ability to generate sounds. A frequently studied fish is the pygmy gourami. It was found that the frequency of sounds produced by this fish coincides with the frequency of sounds recorded (1-2 kHz).
Studies have repeatedly revealed that the lowest frequency sounds, although emitted by specific species, were not perceived by it. However, this does not mean that sound communication of fish is reduced this way. In addition, it is important to remember that this type of communication is significantly affected by distance, environmental conditions including the sound background, and the strength of the signal. A loach produces a sound 40 dB above the threshold of hearing. Other loaches easily recognize it, even though the dominant frequency of these sounds is not heard by these fish. Blue botia emits sound at 300-2000 Hz, and receives signals as low as 100-400 Hz.
You may also be interested in the text about visual communication of fish.
dr inż. (Ph.D.Eng) Aleksandra Kwaśniak-Płacheta
Literature
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Lechner W., Ladich F. (2008), Size matters: diversity in swimbladders and Weberian ossicles affects hearing in catfishes. Journal of Experimental Biology 211, pp. 1681–1689.
Moyle P. i inni (2004), Fishes an introduction to ichthyology, Prentice Hall.
Parmentier E. i inni (2005), Geographical variation in sound production in the anemone fish Amphiprion akallopisos, Proc.R.Soc. B, 272, 1697-1703.
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