BWB – The lateral line organ

Have you ever wondered what that long line is that stretches along the flank of a fishes body? It seems to be just another morphological feature of a fish that changes in shape and curation according to the species. It is, however, so much more than that.

The line is the so-called “lateral line organ”, a long line containing sensory units that detect water movement, vibrations and pressure changes. These units, known as neuromasts, contain tiny hair cells with a gelatinous structure covering them, that deflects through water movement and stimulates the hair movements, which in turn register the changes in environment. It’s a simple system shared by fish and aquatic amphibians but, despite its simple structure, the organ is important for an abundance of reasons.

First of all it allows basic mechanoreception in the water column, giving fish the ability to distinguish weather conditions and depth gradients. Secondly, it facilitates the detection of other organisms in the water which is particularly important when it comes to anticipating the approach of dangerous predators or potential prey.  It also represents an important navigation tool, allowing the fish to navigate using currents, a process called rheotaxis, and maintain coordinated movements for schooling behaviour. In fact, one reason why dolphins are such fantastic hunters of schooling fish is because they can separate the school of fish to seclude and hunt a smaller group – and they do this by blasting the lateral line organ with their sonar. Surprisingly, the organ also serves social communication, allowing fish to interact in their own unique ways.

So the next time you look at a fish, maybe this time you will take a second look at the sensory structure that makes a big difference in how they perceive their exciting underwater world!

By Paula Thake