Fishes produce a variety of sounds using different mechanisms and for different reasons. Sounds may be intentionally produced as warnings to predators or competitors, to attract mates, or as a fright response. These intentionally produced sounds are referred to as vocalizations and many fish species (perhaps hundreds) are known to vocalize. Other sounds are produced unintentionally including those made as a by-product of feeding or swimming. The three main ways fishes produce sounds are by striking or rubbing together skeletal components (stridulation); using sonic muscles that are located on or near their swim bladder (drumming); and by quickly changing speed and direction (hydrodynamics) while swimming. The majority of sounds produced by fishes are low frequency, typically less than 1000 Hz.
Stridulation
Stridulatory sounds are produced when skeletal parts are rubbed together, similar in principal to the method used by crickets to make sound. In fishes, stridulation often occurs during feeding when pharyngeal or jaw teeth are gnashed together. Stridulation of bony parts (teeth or fin spines) may also be done intentionally to produce sound as a fright response or territorial display. Stridulatory sounds can be classified in two general ways, those which are independent of the swim bladder and those in which the swim bladder plays a part in determining the quality of the sound by amplification. The component frequencies of stridulatory sounds range from below 100 to over 8000 Hz, while predominant frequencies are between 1000 and 4000 Hz. Stridulatory sounds influenced by the swim bladder have predominant frequencies well below 1000 Hz.
Some fish, such as the sand seatrout (Cynoscion arenarius), produce sound by using muscles on or near their swim bladder (also called gas bladder). Image courtesy of Grant Gilmore, Estuarine, Coastal and Ocean Science, Inc.
Some fish such as the marine catfish (Arius felis and Bagre marinus) have specialized pectoral fin spines that make a stridulatory squeaking sound. The base of the pectoral fin spine is modified in these catfish. A part of the base, known as the dorsal process, looks like a ridged potato chip. Sound is created when the dorsal process is rubbed against the pectoral girdle. This is commonly observed by anglers who catch a sea catfish.
Sea catfish have specialized fin spines that produce a squeaking sound. Photo courtesy of Don Flescher.
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(From CD Supplement to: Sounds of the Western North Atlantic Fishes by Fish & Mowbray, 1970. CD (c) University of Rhode Island, 2001)
The northern seahorse (Hippocampus hudsonius) is also known for producing stridulatory sounds. In this example, sounds are produced by the bony edges of the skull and coronet which produce snaps and clicks and are possibly amplified by the swim bladder. These are just some examples of fish species that produce sound by stridulation. There are many more that have their own unique methods for producing sounds.
Swim Bladder and Drumming
Among the best known sounds produced by fishes are those made by drumming of the swim bladder with the sonic muscle. The swim bladder is a large chamber of air located in the abdominal cavity in most fishes. However, not all fishes have this organ; sharks and flatfish (e.g., flounders), for example, do not have swim bladders. The swim bladder serves many functions. It is used primarily for regulating buoyancy. Air gets into the swim bladder in one of two different ways, depending upon the species. In some species, there is a duct between the swim bladder and esophagus. The fish comes to the surface and "gulps" air that is directed via this duct into the swim bladder. In other fishes, including all of those that live deep in the ocean, fishes have a special gas gland, or rete mirabile, within the wall of the swim bladder. The rete is made up of tightly packed capillaries, arranged so that those carrying incoming blood are adjacent to those carrying outgoing blood. This allows for efficient exchange of blood gases.
In some species such as the grunts (Family Pomadasyidae), the swim bladder is hypothesized to function as a resonator to amplify stridulatory sounds. Other fishes such as drums and croakers (Family Sciaenidae) have sonic muscles attached to or unattached but very near to their swim bladder for sound production. These muscles, the fastest contracting muscles known in vertebrates, cause the swim bladder to contract and expand at a rapid rate, thus creating the drumming sound. The majority of sounds produced by drumming are short pulses with fundamental frequencies ranging from about 45 - 60 Hz (i.e., goliath grouper and black drum) to about 250 - 300 Hz (i.e., toadfish spp. and silver perch). Higher frequency harmonics produced by drumming are sometimes present above 1000 Hz (e.g., silver perch).
The sonic muscles of the oyster toadfish, Opsanus beta, are located along the lateral surfaces of the heart shaped swim bladder (see Mann lab: http://www.marine.usf.edu/bio/fishlab/bioacoustics.htm). Contraction of the sonic muscles produces a sound similar to a foghorn (see Mann lab: http://www.marine.usf.edu/bio/fishlab/sounds/OBeta.wav). In other species the muscles may be configured differently (such as anchored to the base of the skull) or may be attached to another anatomical feature which is then triggered to vibrate the wall of the swim bladder. For example, marine catfishes possess a modified swim bladder mechanism, called the "Springfederapparat" or "elastic spring apparatus." Thin elastic bones function in sound production. Specialized sonic muscles on the upper surface of this elastic spring cause the vibration of the swim bladder.
Drumming sounds have been described as thumps, purrs, knocks, and pulses all of which occur in different variations depending on the fish producing the sound. In this way fishes are able to produce species-specific sounds which can be used to identify them in recordings.
The toadfish uses its swim bladder to produce a loud sound similar to a foghorn. Photo courtesy of Grays Reef Sanctuary, http://graysreef.nos.noaa.gov
Click either choice below to hear the Oyster Toadfish:
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(From CD Supplement to: Sounds of the Western North Atlantic Fishes by Fish & Mowbray, 1970. CD (c) University of Rhode Island, 2001)
Hydrodynamic Sound
Hydrodynamic sound production occurs when a fish quickly changes direction and/or velocity. These sounds are extremely low frequency and nonharmonic, ranging down to subsonic levels. These sounds are simply a by-product of swimming and probably do not contain information used for social communication. However, it is possible that hydrodynamic sounds may be important to predator and prey interactions. For example, it has been postulated that sharks can detect the low frequency hydrodynamic sounds emitted by fishes. Therefore, schooling fish may inadvertently signal a shark simply by the sounds produced during swimming.
References
Evans, H. D. 1998. The Physiology of Fishes, Second Edition. CRC Press, New York.
Fine, M.L., Friel, J.P., McElroy, D., King, C.B., Loesser, K.E. and Newton, S. 1997. Pectoral spine locking and sound production in the channel catfish Ictalurus punctatus. Copeia 1997(4): 777-790.
Fine, M.L., Malloy, K.L., King, C.B., Mitchell, S.L. and Cameron, T.M. 2001. Movement and sound generation by the toadfish swimbladder. Journal of Comparative Physiology A 187: 371-379.
Fish, M.P. and Mowbray, W.H. 1970. Sounds of Western North Atlantic Fishes. Johns Hopkins Press, Baltimore, MD.
Heyd, A. and Pfeiffer, W. 2000. Sound production in catfish (Siluroidei, Ostariophysi, Teleostei) and its relationship to phylogeny and fright reaction. Revue suisse de Zoologie 107(1): 165-211. Abstract on-line at http://www.ville-ge.ch/musinfo/mhng/page/rszabs001.htm#heyd.
Massachusetts Institute of Technology Sea Grant. 2002. Listening to fish: An international workshop on the applications of passive acoustics in marine fisheries. Massachusetts Institute of Technology Sea Grant College Program, 77 Massachusetts Avenue room E38-300 Cambridge, MA 02139. Proceedings on-line at http://web.mit.edu/seagrant/aqua/cfer/acoustics/proceedings.html.
Tavolga, W.N. 1980. Hearing and sound production in fishes in relation to fisheries management. Fish behavior and its use in the capture and culture of fishes. International Center for Living Aquatic Resources Management. Manila, Philippines.
Tavolga, W.N. 1977. Sound Production in Fishes. Benchmark Papers in Animal Behavior V.9. Dowden, Hutchinson & Ross, Inc. Pages 10-29.
Tavolga, W.N. 1962. Mechanisms of sound production in the ariid catfishes Galeichthys and Bagre. Bulletin of the American Museum of Natural History vol. 124, article 1. http://digitallibrary.amnh.org/dspace/handle/2246/1211.
Zelick, R., Mann, D. and Popper, A.N. 1999. Acoustic communication in fishes and frogs. In: Comparative Hearing: Fish and Amphibians (eds. R.R. Fay and A.N. Popper). Springer-Verlag, New York, pp. 363-411.
Additional Resources
Marine Animal Bioacoustics (Dr. David A. Mann, Marine Sensory Biology Laboratory, University of South Florida)
