Finally a subject I know a fair bit about (as I’m a fish biologist). Here’s an explanation about how fish hear and I’ll end with sort of an answer to Mark’s question. I wasn’t going to bore you all with this the first time around, but now that this post has resurfaced I can’t help myself. So for those not biologically inclined, skip on down to the bottom or skip it altogether.
Although not that well understood, fish (true fish, not marine mammals like whales and dolphins) can hear, but not like you and I. The main “hearing” organs are the lateral line that runs down the side of their bodies and is porous and filled with water, the inner ear called the otolith (they have no middle or outer ear that is connected to the outer body like mammals) and in teleost (bony) fish a gas-filled swimbladder. The lateral line detects low-frequency (<100 Hz) particle motion in the water contacting the flanks of the fish and the otolith, located within the head of fish, is sensitive to frequencies of up to 1-3 kHz. The inner ear is thought to be the main sensory organ involved and is sensitive to vibration rather than sound pressure. The swimbladder of teleost fish (most aquarium fish are of this type) acts as transducer that converts sound pressure waves to vibrations that picked up by the otolith.
Sensitivity to noise and vibration differs among fish species and is largely related to the anatomy of the swimbladder and its proximity or connection to the inner ear. Those fish that don’t have swimbladders (e.g. elasmobranches like sharks and tune) or have poorly developed swim bladders (e.g. many benthic, or bottom dwelling, fish like flounder and sculpins) are least sensitive to sound. Amoung the more hearing sensitive teleost fish some have a gas duct connecting the swimbladder to the otolith (e.g. fish in the herring family) making them moderately sensitive to sound. Minnows and other fish in the cyprinid family (including goldfish) have a bony coupling called Weberian ossicles that connects the swimbladder to the inner ear. These fish are much more hearing-sensitive fish. There are therefore three broad groups of low-, medium- and high-sensitivity fish.
Auditory thresholds, or the minimal level of sounds that a fish can detect at a particular frequency 50% of the time have been measured for a variety of different species obtained in a number of laboratories. The graph below includes goldfish (Carassius), a high-sensitivity fish, Atlanitic salmon (Salmo salar) which hears very poorly and is considered a hearing 'generalist', cod (Gadus morhua) which is known to detect high frequency sounds to at least 38 kHz (although the data below doesn’t represent the ultrasonic detection capabilities of the species), a tuna (Euthynnus) is a tuna without a swimbladder and, like Salmo, is a hearing generalist and finally, a damselfish (Eupomacentrus) which is considered to be moderately sensitive to sound.
As you can see, goldfish, and possibly other aquarium species, has the lowest auditory threshold which for frequencies < 1 kHz is down around the 60 – 80 dB level. How much loud sounds from outside a fish tank maintain their dB level into the tank, I’m not sure. But I’d guess the dB’s don’t get dampened much by the time such sounds reach a fish. Sound travels 5 times faster in water and the glass tank walls and the water will reflect sound waves. One site I looked up said if “you tap the tank, stand or table holding a tank it will send very loud noises into the water, noises that could cause shock and stress to fish”. I guess Pixar got it right in that scene from Finding Nemo when Darla, the brace-mouthed girl, tapped on the fish tank. One site specializing in goldfish says “The tank should be kept where the fish will be spared from excessive noise or thumping(stereos, speakers, etc.).”.
So Mark, to make a long story short, if you are going to put an aquarium in your HT room it would seem fish such as sharks, tuna and salmon would be ok choices (depending on your preferred listening level) and choosing goldfish would be just plain cruel. Thought about the kitchen or bedroom?
Paul
