Diet of the endangered spirlin (Alburnoides bipunctatus) at the centre of its distribution in Europe

Abstract

The feeding habits of spirlin Alburnoides bipunctatus were investigated in a tributary of the River Vistula (Poland). To evaluate size-related patterns of resource use, fish were assigned to three size classes, defined according to size at first maturation: small (29–70-mm total length, TL), medium (71–90mm TL) and large (91–104mm TL). There was a significant ontogenetic shift in the feeding pattern among size classes, marked by differences in the proportion of the main taxonomic groups of prey consumed: small spirlin primarily consumed chironomid larvae, whereas medium and large spirlin showed a preference for Coleoptera, Ephemeroptera and imagines of unidentified insects. The proportion of prey taken from the water column was significantly lower for small- than medium- and large-sized spirlin. This difference was attributed to the benthic habits of small spirlin compared with medium and large spirlin. The shift to open water feeding in spirlin corresponded with sexual maturation, with habitat segregation between the smallest size class (comprising juveniles) and larger size classes (mature individuals). Size-specific changes in the diet composition of this species have not previously been documented.