Background. Ornamental freshwater fish releases constitute a remarkable proportion of the 100 worst invasive species worldwide. Early detection and knowledge of likely introduction vectors and pathways of potentially invasive fishes into sensitive habitats are key for their proper management, hence rapid and correct identification of their occurrence is crucial. Therefore, we tested the hypothesis that a newly-discovered catfish population was that of Clarias batrachus (Linnaeus, 1758), and that this introduction might be of single origin released by aquarium pet fish owners. Materials and methods. In total, 45 specimens of C. batrachus were captured during two electrofishing surveys on 9 and 15 March 2016 by three operators for morphometric and molecular examination. Additionally, 28 specimens were collected for assessing gonadal maturity and sex. They were also measured for standard length and total length and weighed before being dissected. Results. Morphological and molecular analyses indicated that the examined specimens belong to C. batrachus, and that they were likely introduced by aquarium hobbyists. Successful reproduction and establishment of the species are demonstrated by the occurrence of ripe females and their young of the year and juvenile individuals in the catch. Conclusion. Our findings confirmed the presence of C. batrachus in a region with extraordinarily high biodiversity, including the first evidence to indicate the successful establishment of this species in Turkey. An initial first policy and management step would be to ban the importation and keeping of this species in Turkey, thus reducing the risk of further releases. Increased public awareness for the detrimental impacts of non-native fishes would serve to support the policy and field-based management practices to control, and hopefully eradicate this highly invasive species.

ornamental fish, aquatic invasion, walking catfish, Sakarya River, management