Blind cave fish grope their way in the dark

(ORDO NEWS) — Throughout the world, fish of many species live in caves, completely or partially blind. Scientists have found that these amazing animals find their way in much the same way as blind people: they “feel” it in front of them.

Scientists know about 200 species of cave fish : they are found on all continents with the exception of Antarctica and, with rare exceptions, never see sunlight in their lives. As a result, their eyes are tiny or absent at all, and their skin loses pigmentation and looks white or slightly pinkish.

So how do these animals navigate in the absolute darkness of the caves without smashing their heads against the walls and colliding with relatives swimming by?

To find out, an international team of researchers from China, the US and the UK studied the structure and mode of movement of 26 species of cave fish from the genus Sinocyclocheilus ( Sinocyclocheilus ), related to carp and carp.

Different types of Sinocyclocheilus differ in different degrees of reduction of the eyes: in some fish they are simply small, in others they are normal, in others they are completely absent.

However, in the first place, researchers were not interested in the organs of vision, but in the organs of touch of fish – the lateral line.

This line in all fish stretches from the gills to the tail and is a series of sensitive receptors called neuromasts, which help the fish navigate, feel the direction and speed of currents, and detect prey or enemies.

It turned out that in the blind species of Sinocyclocheilus, the lateral line develops more strongly than their sighted relatives, with more neuromasts on one side of the body than on the other.

To find out why such a strange skew was required, scientists launched fish into aquariums and observed their movement.

It turned out that blind fish prefer to move along the walls of the aquarium, lightly touching them with their heads while moving, while the half of the body on which the lateral line was more developed was facing the wall.

Blind cave fish grope their way in the dark 2
Sinocyclocheilus specimen collection sites: yellow dots indicate species with normal eyes, blue dots indicate reduced eyes, red dots indicate eyeless

This means that a blind cave fish behaves in the same way as a person who has lost the ability to see, making his way along the walls to the exit.

Lateral asymmetry arose in different evolutionary lineages within Sinocyclocheilus, meaning that all eyeless species are not close relatives, and this adaptation developed independently in them.

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