By Dr. Hal Schramm

Fish survive in water using the same five senses we use in air—sight, sound, touch, taste and smell. But fish have a modified sense of hearing that is essentially a sixth sense—the lateral line system. How does a fish use the lateral line system? And how can understanding this sensory system benefit astute anglers?

Fish Anatomy 101
Most anglers, whether they know it or not, are familiar with the lateral line. A canal in the skin runs down the fish’s flank. Sense organs in the canal called neuromasts detect water movement or pressure. Pores in the scales (or the skin of scaleless fish like catfish) connect the lateral line canal with the fish’s environment and allow the lateral line system to detect changes in water pressure outside the fish. This line of pored scales is especially visible on the sides of sunfish, black bass, and some minnows.   
scroggins

(LEFT - Bass use the same senses we do, but the lateral line plays a big part in picking up movement and pressure changes in the water.)

Although the lateral line system is named after the canals on the sides of fish, the system is especially well developed on the head. The head canals are located around the eyes, at the top and front of the head, and under the lower jaw.

Most of the head canals are difficult to see, but some are readily visible if you know where to look. Pores on the underside of the jaw—especially visible on bass—open into the head canals. Imagine how functional these canals would be for detecting a crayfish scurrying along the bottom. Pike have conspicuous lateral line pores on the top of their duckbill snout. Pike generally attack from below.   
 
Making waves
Every organism propelling itself on or in the water moves water and, in doing so, creates pressure waves. Fish create pressure waves when they swim by undulating the body or by moving fins. Other aquatic organisms create pressure waves when they paddle with appendages. The lateral line system can detect these pulses of water pressure.
sroggins
A swimming fish also creates pressure waves in the form of a bow wake. This is readily apparent when you see the wake of a fish swimming near the surface or, better yet, when a bass is charging your topwater plug just under the surface. Objects ahead of the fish distort and rebound these pressure waves. The well-developed lateral line system on the head detects these changes and senses what is ahead, even in total darkness.

(RIGHT - Do the multiple swimming tails of the soft-plastic minnows "feel" more real to a bass's lateral line?)

Adding it all up, the lateral line system can detect swimming and stationary objects in the water. Is the system involved in feeding? Apparently so. Sculpins have been shown to detect and attack prey solely on stimuli received by the lateral line system. Northern pike and muskie are typically considered sight feeders. They are attracted to prey visually, but the lateral line system is critical to the final lunge to capture the prey.

Exploiting bass’ sixth sense
The obvious connection between the lateral line system and getting bites is bass detecting your lure in low-light conditions—muddy water, deep water, or at night. Hard-thumping spinnerbaits, bulky jigs with big trailers and wide-wobbling square bill crankbaits are go-to muddy-water baits for top-tier bass anglers. All these presentations have one thing in common—they move a lot of water. Bass can detect that water movement, but there may be a little more to making them bite. Read on.

The hot trend among lure makers is making lures that look like real prey, both in the color patterns and how they move. The appearance of the lures is appealing to bass and to bass anglers who, like their quarry, are visual predators.

Bass haven’t survived for millions of years by making stupid decisions about what they eat. Yes, what a bass sees might signal food or not food. But the pressure waves created by a lure might also signal food/not food. Anglers go to great lengths to select a lure with the right appearance to trip the bass’ trigger—the right size, the right color, the right weight, and the list goes on.  

The function and importance of the lateral line system suggests that anglers should also consider the pressure waves—the vibes—that a lure produces. I learned years ago that the retrieve speed of crankbaits, especially vibrating lipless crankbaits, could make the difference between no bites and lots of bites. I was fishing relatively clear Florida lakes then, so it could have been the visual stimulus.  
bass

(LEFT - Anglers need to consider all senses, including those signals picked up by the lateral line, when selecting the right lure.)

But consider another ever-so-real example: how many times have you been “schooled” by your fishing partner with a crankbait, even though you’ve rotated through several baits that are the same color and run at the same depth. Different brands, different models, different retrieve speeds, different vibes.

The information received by the lateral line system is processed in the auditory lobes of the brain, so it is expected that bass can discriminate a wide range of stimuli. The sound of lures, particularly low frequency sounds that create pressure waves detectable by the lateral line, can turn fish on or turn them away. The different low-frequency sounds produced by a sliding lead, brass, or tungsten weight on a Carolina rig may make a difference to finicky bass. The thud of a One-Knocker XRK50 may draw the attention of bass repeatedly buzzed by regular lipless crankbaits that feature brass rattles instead of a single tungsten.

The lateral line system is a critical sensory component to feeding. The problem for anglers is that while they can easily assess the visual appearance of a bait, they have no way to measure the pressure waves a lure emits. All an angler can do is experiment—different retrieve speeds, different wobble patterns, different bulk, different sound frequencies and patterns—to get dialed in.