A Sixth Sense? Deep Sea Fish Uses Ear-Like System to Detect Movement in Water

The deep sea world has always been a mystery: the absence of light, it's impenetrable depth and the strange creatures lurking underneath. These creatures have evolved to thrive in this alien environment, and a University of Rhode Island (URI) graduate student was able to uncover part of the mystery as she observed new findings on their sensory system.

According to a report from URI Today, graduate student Ashley Marranzino was working with Professor Jacqueline Webb on the sensory system of a particular kind of deep-sea fish called dragonfish. Dragonfish are a wide-ranging group of fish with needle-like teeth and bioluminescent organs.

In particular, Marranzino was curious about how the fish were able to navigate the darkness of the deep sea.

"I was interested in seeing how fishes in the deep sea are adapted to the lower light conditions of their environment," Marranzino, a Denver native with an undergraduate degree in biology from Regis University, said.

"If there is so little light, you would expect that the fish aren't using much of their vision to guide their behaviors. Instead, maybe their lateral line system has evolved to become more sensitive."

The graduate student revealed that the fish actually use a sensory system called the mechanosensory lateral line system. It basically detects water flows and low frequency vibrations in the water, operating much like the human ear. Tiny organs called neuromasts on their skin, head and body sense movements in the sea and help them steer clear of predators as well as find prey.

This system makes them very effective in the water despite of the very low light.

"Having more of these lateral line sensory organs means you're more sensitive to these flows," she explained.

Marranzino used microCT imaging and scanned electron microscopy to examine specimens, concluding that dragonfish must have over 500 neuromasts on a single side of their head and body.

Despite the advancement of science and research, there's still a lot to discover from the ocean's deep end. Just recently, a new glow-in-the-dark species emerged, as published in the journal PLOS ONE.