TULANE (US)—Scientists have found a species of river fish that is able to change into a new shape as its river environment gets dammed up and goes from a fast-flowing river current to the still waters of a reservoir.

“The public hears that dams do things like prevent salmon from migrating upstream to spawn, or that some species are wiped out entirely within a stream when a dam goes in,” says Travis Haas, doctoral student of ecology and evolutionary biology at Tulane University.

“But this is an example of a species that remains in a stream that becomes a lake, and changes in response to it.”

The reservoir-dwelling C. venusta, commonly known as the blacktail shiner has a smaller head, lower-set eyes, a shorter dorsal fin positioned closer to the head, and a deeper body.

Haas studied the aquatic life in eight pairs of river and reservoir sites in the Mobile River Basin and found the characteristics of shiners from reservoirs diverged consistently from those in rivers, indicating that water impoundment ¬ e.g., constructing dams—may be an evolutionary driver acting on aquatic biodiversity.

The study will be published in an upcoming issue of Biology Letters.

Just how long it took for the species to alter its shape is still unknown, but most of the dams in the study have been in place for 60 years of less, Haas says.
“We don¹t know if this is something that would take a couple of years or decades.”

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