Niche overlap between larvae of introduced and native fish in an Australian lowland river
Arthur Rylah Institute for Environmental Research, Department of Sustainability and Environment, 123 Brown St, Heidelberg, Victoria, Australia, 3089.
Email: Alison.King@nre.vic.gov.au
Competition for resources is a commonly stated, but poorly understood, potential impact of introduced fish on native species. Interspecific competition among coexisting larvae may also be high due to their similar morphology, size, swimming ability and dietary requirements at first feeding. This study examined the potential for ontogenetic niche overlaps between two introduced fish, common carp and Gambusia, and two small native species, Australian smelt and crimson-spotted rainbowfish. Stratified habitat specific sampling of larvae and juveniles was conducted in the Broken River, Victoria. All fish were preserved, identified and examined for dietary composition. Australian smelt and carp were found to simultaneously occupy the same nursery habitats during late spring. Rainbowfish and Gambusia shared the same habitats during all developmental stages, and were also observed in mixed species and sized shoals. Major ontogenetic dietary changes did occur for all species. However, there was no evidence of any significant dietary overlaps between these species through ontogeny. Additionally, there was no evidence of introduced species directly preying on larvae of any native species. However, the natural habitat and dietary preferences of native species may have been altered due to the presence of introduced species, and further research is therefore required into the diets of these now coexisting species in allopatric and sympatric conditions.
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