The effects of two different preservation methods on morphological characteristics of the alien channel catfish ictalurus punctatus (Rafinesque, 1818) in European freshwater

Different methods used to store specimens, even for short periods, can notably affect morphometric characteristics such as colour, length and shape. As a consequence, in the case of samples that have to be analysed morphometrically, the right preservation method is crucial. In this study, two comparably easy applicable methods, the effects of freezing and moderate cool storage on morphological traits, were studied on specimens of the scaleless North American channel catfish Ictalurus punctatus, an alien species to European freshwaters of increasing concern. Results revealed that freezing, like preservation with alcohol or formalin, affected the generally considered characteristics (colour, standard length, fork length, total length, shape), while cool storage was shown to preserve most traits without notable alteration, an important difference when studying potentially adapting alien species. Implications are discussed.