Assistant Professor of Biological Sciences Karen Maruska and her PhD student Julie Butler have found something fishy about how cichlid fish fight without their lateral line system, a sensory system normally used to detect water movements. This past October, Maruska and Butler published a paper about their work in the Journal of Experimental Biology. Their paper was highlighted “Inside JEB” and chosen as an “Editor’s Choice” article.
Maruska, a faculty member at LSU for nearly four years, has wanted to conduct an in-depth study of the lateral line system as a form of communication used during social interactions for some time, so when Butler showed an interest in the research, the two decided to team up.
“I’ve wanted to do this project for years but just haven’t had the time. It takes a good student like [Butler] to get all of the work done,” said Maruska.
Studies of the fish’s lateral system date back to the 1930’s, but there has never been a study that dealt with understanding how the fish use the lateral line system in aggressive social situations. For male cichlids, having a territory ensures that they’ll be able to reproduce. Male cichlids that do not have a territory do not mate as much as those that do. To defend these spawning territories from other males, dominant fish perform a variety of behaviors using fin and body motions that produce water movements, which can be detected by the lateral line system of other near-by fish.
To understand how fish use their lateral line system during territorial fights, Butler and Maruska needed to compare fights between two fish with intact functioning lateral lines to fights between two lateral line-ablated fish. So Butler started looking for ways to ablate the fish’s lateral line system. However, this task was not easy.
“There are a variety of ways to ablate the lateral line system, but they don't work the same in every fish species. We needed to find a method that was effective and safe for the fish” said Butler.
Their study showed that fish do, in fact, use their lateral line system to detect their opponent’s movements while fighting. The next step was to see how well fish without the use of their lateral line system would fight, if at all, when paired against a fish with an intact functioning lateral line. Rather than fight, about a third of the lateral line-ablated fish backed down against their lateral line-intact opponents.
“This was the first evidence that the lateral line system is used during aggressive social interactions,” said Butler. “I think this provides more evidence for the role of sensory information mediating fish behaviors. The lateral line system is yet another sensory system that they can use and exploit during social interactions.”
As the study progresses, the team will also produce a paper that documents where in the brain this socially-relevant sensory information is processed. Male cichlids also produce water movement signals during courtship and reproduction. The next step is to understand if females use information gained through the lateral line system for mate preference.
Despite this research being a side project from her normal doctoral studies, Butler said that she’s definitely found some parallels between this project and her dissertation. For her dissertation she’s studying how human-made noises impact fish behavior, physiology, and communication. The first step in her study was to understand how the lateral line system functions during typical social interactions so that she can then test how human-made noise might influence these lateral-line mediated behaviors. Her work with Maruska has enabled Butler to move forward in her dissertation work with a more knowledgeable background about how fish use their lateral line system in day-to-day activities.