Low parasite prevalence in the invasive fish Gambusia holbrooki in riverine and stagnant waters in north-eastern Spain.
Many factors can explain the spread of invasive non-native species, including reduced parasite burdens in recipient ecosystems. From multiple parasite surveys of the eastern mosquitofish (Gambusia holbrooki) in north-eastern Spain (2002-2015), we detected only two parasite taxa from a total of 2320 fish from 58 sites. From mucus scrapings, dissections and histopathology, a single individual of Lernaea sp. and two cysts of unidentified digenean helminths were recovered from three different fish without major pathological signs of disease. In conclusion, this study supports the notion of low vulnerability of wild riverine and lacustrine populations of G. holbrooki to parasites and highlights the importance of reporting negative results in parasitology and invasion science.