Niba: How can we track down missing rivers? Ask fish!

Sometimes when rivers dry out, it can be difficult to know where that water used to flow. But in one case, researchers turned to living fish to solve this problem.

In New Zealand, fish from the genus Galaxias has been found in two separate populations: in the provinces of Otago and Southland. The're all the same species, but the populations are miles apart and not connected by water. So the only way for these fish to have ended up in these two locations is if an ancient river once connected them.

When mountains rose up between the populations, they cut the river in half, dividing it into two separate segments. Those fish will probably become different species eventually through a process called "allopatric speciation," but at the moment, researchers can connect their populations to trace the old river's most likely path - under farmland southwest of the Mataura River.

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