July 10, 2002

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COLLEGE STATION – The placement of the mouth, the length of the tail. These and other traits in fish are showing researchers how the components of an ecosystem lead a species to evolve in their quest for survival.

"The generalities are astounding when you start looking across different continents, different species, different habitats," said Dr. Thom DeWitt, Texas Agricultural Experiment Station fisheries researcher and Texas A&M University Sustainable Coastal Margins Program member. "We are learning about how man's impact on the environment is causing changes in body shape in fishes, and ultimately that could be important in conservation and management planning."

DeWitt's lab is examining various species of fish from Texas, South America and Africa to determine how factors such as predators or water flow result in body shape differences among the same species. He said knowing how body shape relates to the environment helps biologists create ways to manage fish for sustainable use.

"Predators cause fishes to grow longer tails that allow them to swim faster when they are startled, and that makes perfect adaptive sense," DeWitt said. "And the patterns we are studying in our own backyard here in Texas apply worldwide."

In Texas, the Gambusia affinis, or mosquitofish, is one such fish found in the study to have adapted to being raised with predators by growing a longer tail. That's important, he said, because the state has several endangered species of Gambusia.

"Anything we learn about the ‘weed' species can inform us about conservation planning for the endangered species," DeWitt said.

His research group has found similar patterns for a Gambusia species from the Bahamas as well as similar patterns for guppies from Trinidad.

Other aspects of habitat also impose different body shapes, he added. Fish apparently adapt to flowing or non-flowing environments, being in lagoons versus channels, for necessities such as feeding.

"One species of fish (over time) may move its mouth down toward the bottom if the water is flowing and begin bottom feeding while another species of fish will move its mouth up and begin feeding off the surface in a flowing water," he explained.

"When two populations of organisms differ from each other, we used to assume that it was largely genetic. While that is sometimes true, there also is a large environmentally induced component that is non-genetic," he said. "So, ecologists are now gaining a greater appreciation that when you study biodiversity, one has to do both genetics and ecology side by side.

"That sort of integrative approach really allows you to truly understand, hence manage or sustainedly use a natural resource."

Understanding the basic science of fish is important, DeWitt said, because of their role in the ecology of a natural system.

"Because of fish research, we can look forward to having an ecology that is semi-natural because we've recognized what components are necessary for preservation," he said. "But realistically, when natural resources are being used by humans, the best we can hope to do is use them in a way that's sustainable.

"A large part of my research is figuring out what it is we can do in our interactions with the environment that can create sustainable use rather than destructive use," he added.