University of Rhode Island marine biologist Jacqueline Webb gets an occasional strange look when she brings fish to the Orthopedics Research Lab at Rhode Island Hospital. While the facility's microCT scanner is typically used to study bone density and diseases like osteoporosis, it is also providing new insights into the skull structure and sensory systems of fish.
A professor of biological sciences and director of the marine biology program at URI, Webb studies the lateral line system, a sensory system in all fishes that enables them to detect water flows and vibrations in the water generated by predators and prey. The system is contained in a series of tubular canals in the skull and on the body. When flows and vibrations in the environment cause water to move in the canals, the cilia on the sensory organs inside the canals send a signal to the fish's brain.
"If some fish are able to use nonvisual sensory capabilities such as the lateral line to detect prey without seeing, perhaps that makes them more successful," said Webb. "Fish with specialized widened lateral line canals on the head are probably in a position to do well in more turbid waters and under lower light conditions where visually-oriented fishes might be at a disadvantage."
In order to study the evolution of the lateral line system, Webb must first study its structure in great detail. She has previously studied the system using dried skeletons and other methods, but microCT provides much more detailed images in three-dimensions, which can be rotated and digitally dissected to learn much more about skeletal structure.
"CT scanning technology is allowing us to learn about the internal structure of all sorts of animals in a way we could not before," Webb said. "It's as good as holding a perfect skeleton in your hand, but the resolution is so high that we can see minute features of bone structure that have not been appreciated before."
Webb said that one key insight into the lateral line system that she has gained through the microCT scans is the internal geometry of the canals, which are located over the fish's eyes and on the underside of their lower jaw. Some canals are narrow, others are wide, and still others are constricted at some point in the canal.
The Eurasian ruffe, for instance, is an invasive species in the Great Lakes that has particularly wide lateral line canals. "The sensitivity of their lateral line system appears to allow it to outcompete native species, especially in low light conditions," Webb said.
Another invasive species, the round goby, is missing some of its canals, which makes it less able to compete for food in less-than-optimal conditions. African ciclids typically have constrictions throughout their canals. The ciclids that Webb is studying also have widened canals and are able to feed at night, something that is very unusual among cichlid fishes.
"Fishes with widened canals appear to be using the sensory organs in the canals to find prey, so we expect to see indications of this in the anatomy of their brain," she explained. "In the future, we will also use MRI imaging to see if the fish with widened canals have features in the brain that would suggest an enhancement of their lateral line system."
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