Monday, January 01, 2007
There are more than 25,000 species of living fishes. That's more different kinds of fish than any other animal with a spine in the whole history of our planet. Today, we know of more than 1,000 species that make sounds. Scientists who study fish noises have discovered many things over the past 20 years about how and why they make sounds.
How do seahorses make noise? Not through their mouths and voiceboxes and breaths like people. Seahorses actually have bones in their heads that click!
Over 100 years ago, scientists noticed that seahorses make a clicking sound. At first they thought that when the seahorse lifted its head, it made small gas bubbles explode. But using new video techniques, scientists noticed that a sound came out as the top of the seahorses' heads moved in a funny way that rubbed two bones near the top of the seahorse's head and "mane." The bones would pop up and down to make the sound, much like snapping two tiddlywinks together. This way, the sea horse could click to mates, strangers, and also during feeding.
A lot of fish have an air pocket inside their bodies known as a "swim bladder." Minnows, eels, anchovies and goldfish all have swim bladders that they use to keep themselves from sinking in the water. Some kinds of fish use this bladder for more than just staying in place. Some fishes make muscles in their bladders move back and forth very quickly, twitching in the same way the muscles in your jaw twitch when your teeth chatter.
However, scientists have recently discovered one fish has a swim bladder to make sound, but it doesn’t have fast, jittery muscles controlling it. The pearlfish has a much slower muscle in its swim bladder, and it uses the bladder to make sound. The pearlfish doesn’t live like other fish, swimming around in the ocean or lake. It lives inside a live starfish or a tube-shaped animal called a sea cucumber. So, how do these fish talk to each other from inside their houses? That slow muscle inside the swim bladder pulls back, then it releases the front of the swim bladder like a snapped rubber band against a drum. This makes a very strong, low sound that the other pearlfish can hear, even if they are outside the starfish.
One particular fish scientist, Art Myrberg Jr. , spent his whole life thinking about questions like these. Fish sound scientists gathered together last month at a scientific meeting to hear about some things Myrberg discovered about fish noises. Here are some things Myrberg found out about noisy fish.
Fish make sounds for different reasons. They may try to find food, look for mates, or see who's a stranger and who's a friend, using sound. Myrberg studied several species of fish called damselfish. That sounds like it might be a sweet young fish who'd take you home for a cup of tea, but really the damselfish is aggressive, yelling at and chasing strangers.
A male damselfish can chirp and make lots of other sounds. He chirps when he is trying to attract a female to his nest, and he makes chirps and pops when warning strangers away from his area. The damselfish listens for the time between noises to find out if the noise comes from the same or another kind of damselfish. If that other fish is a damselfish, but not a friend, the damselfish gets aggressive and makes a "keep out!" sound. It's a code of communication between damselfish, like talking in humans.
Source: The American Institute of Physics' Inside Science News Service - see the following entry under Archive: 'Fish Stories' (2006) by Timothy Tricas*
2:40pm Sound production and hearing ability in the Hawaiian sergeant fish.
3:25pm Sound communication by the forceps fish, Forcipiger
3:40pm Acoustico-lateralis communication in coral reef butterflyfishes
Info from Timothy Tricas' homepage:
"Our research is focused on the evolution of sensory systems in relation to the natural behavior and ecology of coral reef fishes. The coral reefs of Hawaii and other Pacific regions afford excellent opportunities to study the sensory biology and behavior of marine fishes. One important group is the butterflyfishes (family Chaetodontidae), which occur on nearly all coral reef systems. Some of our current projects include the evolution of a specialized hearing mechanism in butterflyfishes (the laterophysic connection), sound production, neuropeptides as modulators of hearing and lateral line sensory systems, and the evolution of social behavior."
A recently published paper:
Acoustic communication in territorial butterflyfish: test of the sound production hypothesis
Timothy C. Tricas, Stephen M. Kajiura and Randall K. Kosaki
The Journal of Experimental Biology 209, 4994-5004
Published by The Company of Biologists 2006
Butterflyfishes are conspicuous members of coral reefs and well known for their visual displays during social interactions. Members of the genus Chaetodon have a unique peripheral arrangement of the anterior swim bladder that connects with the lateral line (the laterophysic connection) and in many species projects towards the inner ear. This morphology has lead to the proposal that the laterophysic connection and swim bladder system may be a specialized structure for the detection of sound. However, the relevant stimuli, receiver mechanisms and functions for these putative hearing structures were unknown because butterflyfishes were previously not recognized to produce sounds during natural behavior. We performed field experiments to test the hypothesis that Chaetodon produces sounds in natural social contexts. Acoustic and motor behaviors of the monogamous multiband butterflyfish, C. multicinctus, were evoked and recorded by placement of bottled fish into feeding territories of conspecific pairs. We demonstrate that territory defense includes the production of agonistic sounds and hydrodynamic stimuli that are associated with tail slap, jump, pelvic fin flick and dorsal-anal fin erection behaviors. In addition, grunt pulse trains were produced by bottled intruders and are tentatively interpreted to function as an alert call among pair mates. Acoustic behaviors include low frequency hydrodynamic pulses: less than 100 Hz, sounds with peak energy from 100 Hz to 500 Hz, and a broadband high frequency click (peak frequency=3.6 kHz), which is produced only during the tail slap behavior. These results provide a biological framework for future studies to interpret the proximate function of the acoustico-lateralis sensory system, the evolution of the laterophysic mechanism and their relevance to butterflyfish social behavior.
Technorati: fish, hear, mechanism, mates, seahorses, sound, coral, reef, species, swim, bladder, organs, hearing, lateral, line, motion, water, fin, tail, evolution, hawaii, sergeant, forceps, biology, pelvic, dorsal, anal, frequency, social, behavior