Rare Freshwater Fish Hold Clues to Conservation

As the saying goes, there are lots of fish in the sea. But that's only a half-truth. Scientifically speaking, there are also lots of fish in rivers, lakes, streams and ponds as well. Of the more than 32,500 species of fish, 43 percent inhabit freshwater habitats. Taking into account the fact that the water held in rivers, lakes, streams and ponds accounts for only a tiny fraction of the Earth's water—a mere 0.01 percent—freshwater fish are exceptionally diverse.

Scientists don't even have a firm grasp on exactly how many freshwater species of fish there are, the number keeps increasing. In the past 30 years, 5000 new species have been discovered.

Despite their diversity, freshwater fish are in peril. A 2008 study revealed that 40 percent of freshwater fish in habitats across continental North America are at risk of extinction or are already gone. The study noted that 761 fish taxa were in danger and of those, 230 were vulnerable, 190 threatened, 280 endangered and 61 either extinct or survive only in captivity.

Numerous causes underly the alarming decline in fish diversity. Trends such as habitat destruction, habitat fragmentation, collecting for aquarium fish trade, and introduced species all present significant threats to native fish. Additionally, many species are naturally quite rare and may be more susceptible to disturbance and decline than more numerous species. Yet despite these challenges, some naturally rare fish do persist. Scientists are now turning to these species for clues about how they manage to sustain their population in spite of their small numbers.

One rare fish that could benefit from such information is the Picote de Tequila (Zoogoneticus tequila). This small fish survives in a single 4-m-wide pond in the Ameca Basin of Central Mexico. Only 500 Picote de Tequila fish survive and of those, only 50 are adults. This native fish has been pushed to the brink of extinction by another species the Trinidadian guppy (Poecilia reticulata). The Trinidadian guppy was introduced in the Picote de Tequila's habitat in an effort to control mosquito larvae. Now the Trinidadian guppy outnumbers the native Picote de Tequila six to one.

Scientists think that by understanding how naturally rare species continue to sustain their numbers they can learn how threatened species might be managed. Rare species may hold the clues needed to save fish like the Picote de Tequila.

Refs:
Magurran, A. (2009). Threats to Freshwater Fish Science, 325 (5945), 1215-1216 DOI: 10.1126/science.1177215

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