Researcher says
dragonfish have highly evolved system for detecting water flows
URI graduate student Ashley
Marranzino studies the lateral line sensory system of a dragonfish specimen
under a microscope. Photo by Nora Lewis
Little is known about most of the fishes that live deep in the
oceans, where the pressures are extreme, light is nearly absent, and the water
temperatures are especially low. These fishes are difficult to observe in their
natural environment, and it is equally difficult to bring undamaged specimens
to the surface or conduct experiments on them.
Yet a University of Rhode Island graduate student working with
Professor Jacqueline Webb has made great strides in learning about the sensory
system of a prominent order of deep-sea fishes called dragonfishes, a
wide-ranging group of fishes with needle-like teeth and bioluminescent organs.
“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.”
According to Marranzino, fish use a sensory system called the
mechanosensory lateral line system that detects water flows and low frequency
vibrations in the water.
Working somewhat like the human ear, the system uses
tiny organs called neuromasts located on their skin and in canals on their head
and body to detect slight movements in the water, which helps them avoid
predators and find prey.
It also aids fishes in swimming upstream, helps detect
obstacles, and aids schooling fish in sensing their nearest neighbor.
“Having more of these lateral line sensory organs means you’re
more sensitive to these flows,” Marranzino said.
The only previous research on the lateral line system of dragonfishes
was published in German in 1901 and concluded that they have 24 neuromasts. But
by using microCT imaging and scanning electron microscopy to examine specimens
collected by former URI scientist Brad Seibel, as well as specimens from museum
collections, Marranzino conservatively estimates that dragonfishes have more
than 500 neuromasts on one side of their head and body.
 |
| Marranzino examines dragonfish specimens in jars as part of her research on their lateral line sensory system. Photo by Nora Lewis. |
“My findings highlight the fact that these fishes adapted to
their environment by evolving and relying upon this non-visual sensory system,”
she said.
Despite the century-old research on the subject, Marranzino
expected deep-sea fishes to have a large number of neuromasts. That’s because
shallow-water fish that are nocturnal or live in murky environments, and those
that live in caves – all environments where light is limited – have similarly
high numbers of neuromasts.
“But while I’ve shown that their lateral line system is really
important, we still don’t know much about the behaviors they exhibit using this
system,” she added.
Marranzino said that dragonfishes are among the most numerous
fishes on Earth, so it is important to understand how they live and behave and
how they contribute to deep-sea ecology.
“Some of them make a huge nightly migration to shallow waters,
where they are eaten by tunas and other predatory fishes that are important to
fisheries, so it’s important that we understand their biology and their
ecological role in the world’s oceans,” she said.
In addition, Marranzino said that research on the lateral line
system is playing a crucial role in the development of small sensing devices
that may soon be used on autonomous underwater vehicles to help them navigate
and detect objects in the water.
Marranzino presented her research at the International Congress
of Vertebrate Morphology in Washington, D.C., in June and at the Joint Meeting
of Ichthyologists and Herpetologists in New Orleans in July. At the latter
meeting, she earned the annual Frederick H. Stoye Award given by the American
Society of Ichtyologists and Herpetologists for the best student presentation
in genetics, development and morphology.