What Do Fish Hear

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In this, the first in a series of articles about the different senses fish have evolved, we’ll explore what I believe to be the sense fish such as Bass rely on the most, hearing.  More specifically, how fish use their sense of hearing to listen for and find pray, or to detect changes to their aquatic world that signify danger. We’ve all heard about the lateral line on fish and how it serves as a device for them to feel vibration, but did you know fish also have ears?  In fact, certain fish such as shark have a third system for sensing unseen pray that involves the detection of electro-magnetic fields.  These non-visual senses are crucial as often the sense of sight is inadequate due to Low light, water turbidity, dense aquatic weed growth or clever camouflage employed by pray.  One might assume that water, being denser than air, is less efficient at transmitting sound.  In fact, while it is denser, it actually transmits sound better.  Sounds travel through water at a speed of one mile per second; much faster than what we terrestrials experience as made evident when we watch and then hear lightening.  It’s no wonder then that fish get spooked by sudden intense sounds.  Water conducts sound at a rate 4,818 feet per second, almost five times the rate sound travels through air. However, since water is 800 times denser than air, it only allows one ten-thousandth of sound travelling by air to penetrate.  For fishers this means fish most likely won’t hear our conversations, but will hear any sound generated in direct contact with water such as lures landing on the surface, the hum of trolling motors, and anything that causes a boat to resonate such as a foot step or dropped tackle on a deck.  The ears of a fish are enclosed in a bony structure in the skull just behind the eyes. Because fish are made up mostly of water and almost the same density, sounds also pass easily through a fish’s body to their inner ear.  Sounds are also magnified by a fish’s swim bladder, which is an elastic membrane filled with gas that resonates sound like a drum.  Even the most distant sounds can be magnified by the fish’s swim bladder and then heard indirectly through their inner ear. When we listen underwater sounds seem to originate from between our ears.  Because we are used to processing sound that travels at one fifth the speed, our brains are unprepared to make sense of what our ears are sensing.  Fish, on the other hand, have little difficulty discerning a familiar sound such as the clicking of a crayfish’s claws from over 40 feet away.  Since fish have evolved in a world where sound caries quickly, their processing and reaction speeds have  also developed accordingly, which explains why surface baits such as frogs are tracked down and engulfed by Bass in an instant even if hidden from sight by aquatic vegetation.

Fish are attracted to things they hear that resemble potential food.  They will often move closer to satisfy their curiosity even if they aren’t hungry.  Like a baby, their mouths are their primary tool for directly exploring their world through senses such as smell, feel and taste.  To fish, everything is real.  They have no concept of artificial.  Fish can be conditioned to avoid lures that sound or taste a certain way through repeated negative experiences involving being hooked and released, but they don’t have the capacity to understand that there’s an entire industry busily developing and selling lures that mimic their pray.  That’s why even a simple change in lure colour can reawaken a school of fish into striking the same basic lure that was just used to catch a number of their clan.  Use sound to your advantage by working baits in ways that mimic sounds given off by pray.  Avoid creating totally unnatural sounds that cause predatory fish to drop their habitual offensive posture.  Apex predators fear little in their underwater world, and are always curious to learn.  However, they also remember what it was like to be pursued as a fry by something much larger, and it’s these sonic reminders that you want to avoid transmitting.  Next month I’ll explore the role of the lateral line, and how it too serves fish in their pursuit of food and avoidance of danger.

 

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