How they hear, what they hear and what they don’t hear — and why it matters
Water is an effective medium for sound transmission, and fish have a dual-receptor hearing system that equips them to detect and use sounds in water to their benefit. Research on production and effects of sounds in fish are ramping up, but information useful to anglers remains elusive.
How fish hear
Fish translate sound waves into information the same way humans do — by activating nerve cells lining the inner ear. In humans, the bones of the middle ear (the ossicles) mechanically transfer movement of the ear drum to the inner ear that stimulate nerves. Fish lack an outer and middle ear, but they don’t need them because living in an acoustic medium (water) and being largely made of water allows the sound waves to pass readily to the inner ear. Here, the sound waves cause the ear bones (otoliths) to vibrate and stimulate the inner ear nerves.
Some fish, like minnows and catfish, have bones that convey the vibrations of the swim bladder to the inner ear. The swim bladder functions as an ear drum, and the bones — called the Weberian apparatus — function like the human middle ear.
Fish also hear via the lateral line system, which detects low-frequency sounds, actually water movement. The lateral line is often conspicuous as a line of pored scales from head to tail on the fish’s flank. Although rarely visible, the lateral line is well developed on the head of the fish.
What fish hear
Sound detection is an effective sense for bass detecting their environment. Sound is directional, and sound waves travel almost five times faster and much further in water than in air. Although traveling slower in water than light, sound moves through clear and muddy water and transmits much further and faster than chemicals that can trigger feeding responses via smell and taste. Hearing provides real-time environmental information.
While fish with a Weberian apparatus hear sound with frequencies up to 13,000 cycles per second (also called Hertz, abbreviated Hz), peak hearing of largemouth bass, according to unpublished data cited in Dr. Keith Jones’ book Knowing Bass, is around 100 Hz, with little sound detection above 600 Hz. For comparison, humans hear sounds ranging from 20 to 20,000 Hz.
So that leads to the key question for using sound to catch a bass: can bass hear it? With a hearing range restricted to the lower 5% of the angler’s range, what you hear may not be what the bass hears.
With the exception of a dead worm or minnow on a hook under a bobber, all lures produce sounds that bass can hear with the inner ear or the lateral line. Topwaters splash, spit and gurgle; spinner blades move water, and any retrieved plug, even a solid, wooden one, moves water and generates clicks and rattles from attached hooks. These low frequency sounds can be detected by the lateral line and the inner ear.
The 1960s and 1970s ushered in “rattling baits” — molded plastic lures with internal sound chambers containing one or more metal rattles. Manufacturers claimed some version of “baitfish mimicking sound”, and bass anglers reported catch rates far surpassing catches on most “silent” baits. The market broadened, and virtually all lure companies now make noisy lures.
More recently, fishing technology hit a new plateau with lures with sound-emitting chips and Hydrowave™ underwater sound systems that replicate baitfish sounds.
The right sound
While sound production is a big deal for anglers and the sportfishing industry, the available — and very limited — science says bass can’t hear the high-frequency rattles and the synthesized baitfish sounds. The dominant frequency — the frequency of the sound spectrum that carries the higher energy level — of these lures and sound-production systems is beyond the bass’ detection frequency.
But according to information shared by Steve Quinn, a fisheries biologist, avid bass angler and writer, the dominant frequency of the sound made by a school of shad is also well beyond the supposed detection range of largemouth bass.
While much of the information I share in this column is an attempt to share known fish biology information so anglers can better understand the fish they try to catch, I think the biological knowledge of sound detection has a long way to go to provide information useful to anglers and lure and sound-production system manufacturers. For starters, the sound-frequency spectrum that largemouth bass and other sportfish can detect needs to be assessed or reassessed. A second question is whether the dominant frequency is predictive of behaviors such as feeding or striking a lure. Bass eat a lot of shad, even though the dominant frequency of sound produced by a school of shad is not detectable by bass.