A Little Bit More
You may never have noticed a fish's lateral line before, but a quick look at the side of most fish reveals a thin horizontal line, a sort of division between upper and lower scales. That's it!
Lateral line.
The lateral-line system in fish consists of a series of sensory cells (neuromasts) usually running along both sides of a fish's body. Typically, lateral-line systems are mucus-filled tubes or canals just under the skin that have contact with the environment through pores in the skin or scales. A nerve along this line sends branches into the canal that feed the incoming stimuli to the fish's central nervous system. This system greatly expands the area of tactile (touch) perception by making it possible for the fish to interpret its environment without actually touching an object. The lateral-line helps fish navigate through murky water, find food, travel at night, stay together in a school, avoid enemies and even sense water temperature. In many fishes, the neuromasts extend along the fish's head as well as sides, although these are not always as obvious.
When the neuromasts are at rest, they send a continuous series of nerve impulses to the central nervous system. When pressure either increases or decreases due to a disturbance near a fish, the nerve impulse pattern changes; the fish registers the change, and takes appropriate action.
One way humans can begin to understand the lateral-line system, to a degree, is to note that the pressure on our bodies from a strong wind is similar to what a fish senses from various disturbances in its environment. Fishermen are well aware of a fish's ability to interpret its environment and act accordingly to avoid spooking the fish they're stalking. Some trout fishermen prefer to do their fishing at night when their quarry is less skittish and a trout's ability to find food in the dark, swift waters of a trout stream is clearly demonstrated by the fish they catch. Just think how effective their sensory system is—could you find and grab a tiny fly floating in a nighttime trout stream?
Activities
Sixth Sense
Objectives: Get a feeling for what a sixth sense might be like
Materials: blindfold
Humans have five senses; sight, hearing, feel, taste, and smell. Since mammals don't have a lateral line system, it's very difficult, maybe impossible, to convey just what it must be like to have this added ability. After all, could you really convey what sight is like to someone who has never been able to see? But maybe we can provide an approximation of what the lateral line system is like by trying one particular activity.
For this activity, you'll need to blindfold a person and have them move within a room. Make sure there is some open space along one wall and then blindfold a willing subject. The object of this activity will be for the blindfolded person to try and determine when he/she is really close to a wall without touching - they can use other senses other than eyesight.
Once blindfolded, move the subject around a bit so they lose track of exactly how far they are from the selected wall. Now face the person toward the wall and instruct them to walk very slowly toward the wall (you need to assure them that you won't allow them to bump into the wall). As the subject slowly walks toward the wall, they need to use all of their senses to determine just how close they are (everyone in the room needs to be extremely quiet). If the subject moves cautiously and carefully, just before arriving at the wall, they should be able to "feel" its presence just beyond their body. Not everyone is good at this but with a few trials many will be able to do this activity surprisingly well. Although people will be able to do this exercise, they'll have trouble explaining just how they're able to do it. Be sure to have them explain, as well as they can, what sensory cues they're using to accomplish this activity.
Granted, it's not like a fish's lateral line system, but maybe it will help you get a general sense of what that sixth sense might be like.
Key Concepts
Predator/Prey Relationships, Structures and Functions
Questions
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Posted by Chris Gavin on May 03, 2006 at 11:50 AM
Q: Are there any known distance limitations to the lateral line's perception? Any rules of thumb?
A: Interesting question. The lateral line picks up physical distortions of the water in its environment so it isn't a matter of how far away the distortions originated, but whether or not they are strong enough to arrive at the fish's body and stimulate its lateral line system. An insect falling on the water isn't going to create much distortion but a boulder that falls into the water will. Hope this helps.