Mezquital: El Toboso
Conservation: Back in 2006, the spring had an abundant and healthy population of Characodon lateralis, which were visible all along the creek, courting males could commonly be seen along the edges. When I visited in 2007 something was different, somebody had introduced Gambusia senilis, and by the next year, the population of Gambusia had bloomed and the Characodon numbers near the main spring had significantly decreased, a trend that continued over the years until no more Characodon were to be seen above the man-made ponds. There was however a heavily planted segment of the creek below the ponds that still for many years hosted a healthy population of Characodon, and this is the place we visited this year. It was shocking to find out that after a vigorous collecting effort that extended for a couple of hours, we were just able to collect a single male and a single female (pregnant) of C. lateralis. I dare to say that this population has no long-term viability unless exotics are quickly removed.
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