The North American fathead minnow Pimephales promelas in Europe: potential invader or a benign non-native fish?

Abstract Fish introductions can result in their establishment in the wild, with invasion risk assessments identifying those non-native species with a high probability of developing invasive populations. The North American fathead minnow Pimephales promelas was imported to Europe for decades for both ornamental and scientific (toxicology research) purposes. In North America, the fathead minnow has been introduced widely into areas outside of its natural range, where it has expressed considerable plasticity in life-history traits when establishing new populations. In Europe, established populations are present in the wild but remain limited in number, with the paucity of life-history data on these European populations leading to their risk assessments being based on minimal data resulting in low confidence. The aim here was to overcome these data deficiencies by analysing the life-history traits and morphologies of four European P. promelas non-native populations (two in England and one each in the Netherlands and Belgium), with risk screenings completed based on these data. All populations consisted of small-bodied individuals (