Gut content and stable isotope analyses provide complementary understanding of ontogenetic dietary shifts and trophic relationships among fishes in a tropical river

Aaron M. Davis, Melanie L. Blanchette, Bradley J. Pusey, Tim D. Jardine, Richard G. Pearson

Research output: Contribution to journalArticle

Abstract

1. Despite widespread recognition of the role of body size in fish trophic ecology, little attention has been focused on this issue in isotopic studies, particularly in tropical systems. 

2. We used analyses of stomach contents and stable isotopes to examine size-related shifts in diet in a terapontid fish assemblage in the Australian wet-dry tropics. Stomach content analysis identified substantial ontogenetic dietary shifts in all species, corresponding to changes in body size-isotope trajectories for two species. Shifts away from relatively specialised diets of heavily 13C-depleted insect larvae to consumption of a range of items across multiple basal carbon sources appeared to be the proximate cause of observed isotopic changes. 

3. Allochthonous organic matter in the form of C3 riparian vegetation was particularly important to smaller terapontids before larger fish shifted to a broad range of dietary items and similarly broad range of basal carbon sources. 

4. While there was general agreement between δ 13C and stomach content analysis, there was minimal concurrence between the latter and δ 15N isotopic derivation of estimates of trophic position. Due to factors such as omnivory, isotopically overlapping basal sources and uncertainties about rates of isotopic fractionation in both predator and prey species, stomach content analysis provides an essential complement to isotopic methodologies in tropical systems. 

5. Given that basal sources supporting any individual species can change markedly with ontogeny, consideration of intraspecific, size-related variation is necessary in isotopic studies of food web structure.

Original languageEnglish
Pages (from-to)2156-2172
Number of pages17
JournalFreshwater Biology
Volume57
Issue number10
DOIs
Publication statusPublished - Oct 2012
Externally publishedYes

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