Young Allis Shad Alosa alosa (Clupeidae) Would Not Be Euryphagous: An Assessment of Juvenile Diet and Prey Selectivity under Riverine-Type Conditions

Allis shad Alosa alosa hatches and develops in freshwater before migrating to the sea during its first months of life. Some field research works dedicated diet species put forward that young stages allis feed mainly on zooplankton, being opportunistic euryphagous; their would diversify through ontogeny relation growth. However, these assumptions have never been confronted availability prey, exact age fish was unknown. In this work, we reared under seminatural conditions, from 6 10 days posthatching until nearly 3 old, a trophic environment representative natural river. The rearing structures were designed as artificial rivers, supplied continuously by riverine water zooplankton prey. Additional produced separate basins added daily structures. One river used rear 2018, experiment conducted two batches 2019 (one batch per river). We described nekton communities potential prey available for sampling every week, compared data with stomach contents captured at one old describe selectivity. Our results suggest should not be considered feeding, since clear selectivity observed both ages. One-month-old highly selected cladocerans, probably because they are easy catch age, when swimming abilities limited. Feeding selection drifted towards other taxa (dipteran larvae, ostracods, and/or copepods), whereas cladocerans no longer preferred. density competition may entice two-month-old enlarge taxa, including benthic organisms, while one-month-old do seem able shift fast absence cladocerans. Thus, highlights feeding challenging month