Understand Lateral Lines to Help You Catch More Fish

As 2020 careens toward its long-awaited end, lyrics from Bobby McFerrin’s 1980’s classic “Don’t Worry Be Happy” conjure a lightened mood and a mantra of hope. I mean, go ahead and try to read those lyrics without matching the whimsical, whistling beat of the original tune. I dare you.

Not bad, eh?

That is, unless you’ve previously fallen victim to the song’s rendition by Big Mouth Billy Bass. Yes, that infamous, obnoxious, motion-sensing rubber novelty fish, perhaps hanging in the restroom corridor of your local fishing bar or, Heaven forbid, taking up real estate in your man cave following a less-than-stellar Father’s Day gift. Ironically, while you can turn off the motion detector of Ol’ Billy Bass, for actual living fish, perceiving motion, or vibration and current through water, is critical to allow fish to move, eat, and ultimately, survive.

Many anglers are familiar with the lateral lines of fishes, which detect motion underwater. However, in certain angling situations, understanding the science behind this mechanoreceptor system could improve your lure selection and angling success. If nothing else, you might impress folks at the bar. Let’s set one (or both) of those scenarios in motion.

The Thin Sensory Line

The lateral line system is one of two mechanosensory systems fish possess. The other is their inner ears, which function somewhat analogously to ours, providing equilibrium, balance, and hearing. Intriguing in its own right, but let’s focus on the lateral line.

Due to water’s density, hydrodynamic waves and vibrations are enhanced when moving through it relative to air or other substrates. Interestingly, the origin of the lateral line traces back in evolutionary time to before fish even had jaws. But, not before fish developed hair cells.

Wait, what? Hair cells? A mullet wig might be fitting for Big Mouth Billy Bass in a dingy karaoke bar, but don’t expect a real-life living fish to grow one anytime soon.

To clarify, sensory hair cells are a key component of the lateral line and are not actually “hair.” Rather, these cells have hair-like filaments called cilia that extend upward from each hair cell. Individual hair cells are organized into bundles (neuromasts), with a gelatinous cap (cupula) that contains all cilia from the multiple hair cells within a neuromast. Picture a tiny, dome-shaped mold of Jell-O with hair-like filaments embedded vertically throughout the jiggly mass. Poke the Jell-O hard enough and the embedded filaments wiggle with the jiggle. That is, the body of hair cells associated with those filaments rests underneath the dome of Jell-O, which connect with other supporting cells attached to sensory nerves. Here’s a good diagram for your visual senses.

When hair cells are stimulated the nerves carry signals to the brain, which interprets the original vibration and responds to the movement accordingly. For example, a fish can move toward prey, away from predators, or in sync with other fish in a school, etc. The lateral line system detects motion from other moving objects, as well as waves reflected back to the fish where the motion originated.

Line ‘em up

On many fish species the horizontal lateral line is readily apparent with the naked eye and generally runs mid-body from the gills to the tail. Look close enough and you might be able to make out individual dots that form the line—these are actually pore openings to a canal. Rather inconspicuously, the lateral line system also extends forward to pores in the bones of the head.

Within each canal, the pore openings expose neuromasts to vibrations in the surrounding water while remaining sheltered below the scales and/or skin. This means that canal hair cells are not constantly stimulated by water moving across the skin, rather they are more effective when the fish, or water around the fish, is moving quickly or with greater force. Still, the lateral line system isn’t relegated to just the “line.” Inconspicuous groups of sensory cells are also located across the surface of the skin. These “superficial neuromasts” are not protected within canals, so they are more sensitive to small movements in calm water.

In juvenile fish, superficial neuromasts develop first, and then, based on environmental and genetic characteristics, some superficial neuromasts transition to canal neuromasts. For example, trout that live in swift moving rivers have more canal neuromasts, while goldfish raised in stagnant tanks have mostly superficial ones. Further, due to conditions where they are born and raised, wild steelhead have more neuromasts overall compared to hatchery-raised steelhead. This likely contributes to improved detection of predators and prey, and thereby, increased survival by wild fish compared to released hatchery fish.

The bottom line

Okay, so that’s cool (at least I think so), but how does any of this information help anglers?

While it’s a critical sensory system for most fish species, the lateral line does not act alone—vision, hearing, and smell are also important senses, especially regarding lure detection. However, under conditions that limit one or more of a fish’s other senses, detecting and locating perceived prey movement and vibrations can be the difference between strikes and no strikes, hook-ups and missed hook-ups.

For a lot of fish species, acoustic and chemical signals can be recognized at the greatest distance, followed by vision, and then vibration via the lateral line system. However, when vision is significantly limited by the dark of night or turbid water, detecting vibration becomes much more important. I doubt you’ll be fishing for blind cave fish anytime soon, which rely almost exclusively on the lateral line to survive, but let’s take muskellunge for example. Night fishing for these toothy critters is increasingly effective during summer when water temperatures are high, the sun is powerful, and daytime boat traffic is a pain in the ass. Experienced nighttime muskie hunters know to track lunar cycles—new and full moon periods generally produce better action. During a new moon, when fish night vision is usually most limited, loud and wobbly lures or big, double-blade bucktails can up your odds to hook the “fish of 10,000 casts.” In fact, research has shown that visually-limited muskies require the lateral line to pinpoint a target and strike. So, even at night, don’t forget your boatside figure-eight or similar motion, even if you or the fish might not be able to see the lure.

Similarly, foraging lake trout rely heavily on vision, but at night or in deep water be sure to use lures with plenty of motion. Lakers will pick up and follow hydrodynamic trails left by prey fish or your lure, so changes to retrieve or trolling speed can trigger a strike from a trailing fish.

Similar concepts apply to fishing in muddy, turbid water, or even around thick, submerged vegetation. Lures with strong vibrating qualities, such as spinners and spoons or lipless and square-bill crankbaits, are good choices when targeting fish in those scenarios. Further, if you’re targeting fish with crankbaits in murky water, you likely need to be more accurate when casting to cover—many lures that include rattling features produce frequencies outside the auditory range of gamefish. A retrieve close to the location of a fish is needed for them to detect and locate your lure via vibration, especially when their vision is also limited.

Every lure produces its own distinct vibration signature. Many of those catch fish. However, any angler who’s been at it for some time will likely recognize that certain lures throw off a thump that just hits differently than others and seems to attract fish almost in spite of themselves. The Vibrax Spinner, Whopper Plopper topwater plug, and Shad Rap diving crank are just a few examples of these wavelength hacks.

The End of the Line

Nobody is going to mistake the dated, motion sensing technology of Big Mouth Billy Bass for a feat of engineering. Far from it. However, nature’s technology exhibited by the motion sensing lateral line system of real, swimming fish not only stands the test of evolutionary time, it also helps anglers put fish in the boat and keeps tackle manufacturers in business. In fact, today’s engineers approach the lateral line as a feat of bioengineering. Researchers are mimicking properties of fish lateral lines to develop artificial lateral lines. This technology can permit unmanned submersibles and underwater robots to operate autonomously.

That’s cool. So is catching fish in conditions where understanding the lateral line gives you an upper hand. Big Mouth Billy Bass, not so cool. But, just remember, next time you’re startled and annoyed by a singing rubber fish:

“…It will soon pass, whatever it is
Don’t worry, be happy”

Or just flip the off switch. And in the meantime, go fish, and put out some positive vibes!

Feature image by Tosh Brown.