Fish Sensory Systems: Part 3

The lateral-line system detects water movement. This ability may help this bluegill find prey but also alert it to an approaching predator.

Hearing and the Lateralis system

Fish rely on their senses to survive, and in particular, to find food in their underwater homes. Part I of this series explored vision, a very fast and accurate sense for detecting objects in the environment, but also a sense quickly impaired by changes in water clarity. Part II explored how taste and smell are involved in feeding and concluded that chemical cues may be important for accepting or rejecting objects as food but probably have a relatively minor role in detecting prey or attracting fish. This final segment explores fishes’ ability to detect sound and water movement. These senses may have much more to do with feeding than formerly known or even thought.

Fish ears: Detecting sound

Sound travels farther and about five times faster through water than air. Water is a very good medium for sound transmission, and fish are well equipped to detect it. Most sportfish hear a slightly narrower range of frequencies and have a slightly higher-intensity threshold than humans.

Fish lack an outer ear, eardrum and the middle ear bones but, like humans and other vertebrates, have an inner ear. The fish’s inner ears, one on each side of the head, consists of three semi-circular canals. Each canal connects to a chamber containing a small bone — the otolith — that floats on a lining of nerve cells. Sound vibrates the otolith and is transformed into neural information. Even though the paired inner ears are close together, fish are thought to have directional hearing.

The lateral line system: detecting water movement

Most anglers are familiar with the lateral line running down the side of the fish. The lateral line is a canal in the skin connected to the environment by pores in the scales or the fish’s skin. Inside the canal are sense organs that detect the force and direction of water movement. This system very effectively detects water movement and low-frequency sound.

The canals are also well-developed on the head of the fish, and the system of lateral line canals and head canals is called the lateralis system. Although the head canals are inconspicuous in most fish, openings to the head canals can be seen as pits on the underside of the lower jaw of largemouth, smallmouth and spotted bass.

The canals on the head expand the functionality of the lateralis system by detecting objects in front of the fish as well as to the side or behind. Everything that moves in the water produces pressure waves. As a fish swims forward, it creates a bow wake. Objects in the path of the fish reflect this bow wake, and the head canals detect a change in water flow. Other organisms moving in the water — like a school of shad, a sunfish, or a crayfish on the bottom — also create pressure waves that are detected by the lateralis system.

The lateralis system is effective for detecting prey, but it also may be important for capturing prey. Recent research indicates that muskies rely on vision to detect and approach prey, but the lateralis system is critical to the final lunge to close the deal. Blinded muskies strike at prey swimming in close range, and prey capture-efficiency is the same as for fish with vision.

Undervalued and underexploited 

Ten years ago, fishes’ ability to use hearing and the lateralis system to detect and capture prey was largely overlooked by anglers and even biologists who study fish behavior. Like vision, hearing and the lateralis system provide both real-time information and allow predators to accurately locate prey. But unlike vision, hearing and the lateralis system are not impaired by changes in water clarity.

That was then. Anglers now select lures based on “moving water,” electronic devices play feeding sounds into the water, and chips in crankbaits call in fish. And there are the silenced lures that only emit the low-frequency “sounds” of water displacement.

Putting it all together

Fish live in a dynamic environment. Regardless of the water clarity, the flow or the location and behavior of their prey, fish must eat. It makes sense that fish would use different senses under different conditions. It also makes sense that a fish may use multiple senses to feed or strike. I learned a long time ago that retrieve speed can be critical, particularly with lipless crankbaits. Often a certain retrieve speed drew numerous strikes, while a slightly faster or slower retrieve hauled water. I don’t know if sound, vibration (water movement) or the visual stimulus triggered the bites. Maybe all three. But reflecting on those trips reminds me to consider appealing to multiple senses when I’m looking for that next bite.

About Hal Schramm 182 Articles
Hal Schramm is an avid angler and veteran fisheries biologist.

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