Imagine if you could not only hear movements all around you but if you could actually feel them too.
And not just feel movements but also sense objects and obstacles around you too.
It wouldn’t be quite as good as having eyes in the back of your head. But pretty close.
No one could sneak up on you. You’d bump into things a lot less.
We might wish for such a special physical ability. But most fish already have it, in a unique sensory system that only they have.
You can see where this “sixth sense” occurs on a fish. It’s the line down the sides of their bodies called the lateral line.
In this lateral line are sense-receptor cells called neuromasts. The neuromasts have tiny hair cells, similar to what you have in your inner ear. These cells are connected to nerves that run to the fish’s brain. Even the slightest wave energy in the water bends the hair cells in the corresponding direction and that sends a message to the fish’s brain telling it where the wave energy came from.
Just by swimming, a fish creates wave-energy impulses in the water. Like a boat’s bow wave. Lateral lines let one fish detect these impulses of other fish – not just detect the movements but understand the speed and direction. Thus, lateral lines help fish avoid predators. And lateral lines help to enable schooling fish to swim in tight schools, moving as if synchronized in a one huge mass.
Another point about that wave-energy impulse – that bow wave – created by a swimming fish: when that wave impulse hits an object, something like an echo impulse bounces back at the fish. The fish’s lateral line can detect that as well. That can tell a fish at night where rocks, reefs and other obstructions are. It also can tell a fish in an aquarium where the glass is.
Lateral lines generally extend from a fish’s gills back to its tail. Some are more obvious than others. Some are ruler straight, others flow back in an arch. Variations in the lateral line’s shape can help to distinguish closely related species.
During your next Maritime Aquarium visit, make it a challenge to find the lateral lines on the fish in all the galleries. They’ll be easy to see on – say – the cod and pollock in the “Go Fish” exhibit. But you’ll have to look closely to see the lateral lines on – for example – the red drum (in the Ocean Beyond the Sound “shark tank”) and the sergeant majors, hogfish and other reef fish in the Tropical Travelers exhibit.
– Dave Sigworth, Maritime Aquarium publicist
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