The diet of the alien channel catfish ictalurus punctatus in the river arno (Central italy)

The North American channel catfish Ictalurus punctatus has been widely introduced to Europe, but no in-depth studies on its ecology and potential impacts in the introduced European range have been carried out. In 2016, 248 specimens of I. punctatus were collected from the Arno river, Florence (Central Italy), and analysed for their length, weight, size, sex, and stomach contents to assess their diet. Specimens < 30 cm total length (TL) represented the majority of the sampled population. Detritus and phytoplankton dominated the diet, while in larger fish (≥ 30 cm TL) two invasive alien species, the topmouth gudgeon Pseudorasbora parva and the red swamp crayfish Procambarus clarkii, were dominant prey items. Diet composition of I. punctatus significantly varied among size classes, but not between sexes. The results indicate an opportunistic but gape size limited feeding behaviour, suggesting an intra-specific competition avoidance mechanism.