Cooperative Fish and Wildlife Research Units Program: Tennessee
Education, Research and Technical Assistance for Managing Our Natural Resources

The Sharptooth walking catfish (Clarias gariepinus) is native to parts of the Middle East, Asia, and Africa but is one of the world's most invasive freshwater fish species. The species’ ability to invade is partly due to its ability to breathe atmospheric oxygen, thereby avoiding hypoxia or poor water quality in receiving waterbodies; further, it can crawl over moist land to disperse to new systems. In 2018, two individuals purported to be Sharptooth walking catfish were collected and identified within the Canal de Patillas, a canal in the Guayama municipality in southeastern Puerto Rico. Several other specimens were also collected the following year. Given that this invasion was in its infancy, environmental DNA (eDNA) surveillance was employed as a rapid and efficient surveillance tool to help delineate the extent of this invasion. Water samples were collected and analyzed for Clarias eDNA from 63 sites encompassing a wide range of habitats in canals, lakes, and a river surrounding the area where they were first reported. Using eDNA-metabarcoding, we detected Clarias eDNA at 40 of the 63 sites throughout the sampled waterbodies. Furthermore, our molecular analysis indicated that the Whitespotted Clarias (C. fuscus) is the likely invader, and the original specimens, classified as C. gariepinus, were misidentified based on the use of morphological rather than genetic features for species classification. Environmental DNA surveillance indicated that the distribution of Clarias catfish in this system is substantially more extensive than previously documented. These findings suggest that additional survey efforts could help determine the invasion's full spatial extent and leading edge to inform the scope and scale of any potential management responses.