Ontogenetic dietary shifts of fishes in an Australian floodplain river

La Trobe University Faculty of Science, Technology and Engineering Murray Darling Freshwater Research Centre

MDFRC item.

The early life of fishes is marked by rapid development when individuals are thought to optimise their success through ontogeny by altering ecological niches and resources. Since most fish larvae are thought to require small prey items at first feeding, competition for potentially limiting food resources may occur between species creating a juvenile bottleneck, which may, in turn, influence future recruitment strength. The diets of the early life stages of most Australian freshwater fish are poorly known. The present study investigated the ontogenetic dietary patterns of six species of fish in an Australian floodplain river. A large proportion of first-feeding larvae of three species (Murray cod, Australian smelt and carp) were able to feed externally while still retaining their yolk sac. All species demonstrated major dietary shifts from newly hatched larvae through development into juvenile stages and adulthood. Only a few minor overlaps in diet were found, with greater overlaps commonly occurring between sequential stages of the same species, reflecting subtle ontogenetic changes. Despite two co-occurrences of an introduced and a native species using the same rearing habitat as larvae, dietary preferences did not significantly overlap, suggesting that a recruitment bottleneck caused by competition for food resources is unlikely for these species.