Dietary tracers and stomach contents reveal pronounced alimentary flexibility in the freshwater mullet (Myxus capensis, Mugilidae) concomitant with ontogenetic shifts in habitat use and seasonal food availability
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We investigated ontogenetic and seasonal variations in the diet of the freshwater mullet (Myxus capensis) across a river–estuary interface using dietary tracer (stable isotopes and fatty acids) and stomach content analyses. Two hypotheses were tested: (A) the freshwater mullet diet shifts as individuals grow and migrate from the estuary to the river, and (B) the dominant food resources utilized by freshwater mullet vary through time, mainly as a function of the seasonal changes in the availability of preferred food items in each habitat. Both hypotheses were supported, as our results indicated broad dietary flexibility by M. capensis, with utilized food items ranging from benthic microalgae to insects depending on habitat and seasonal patterns in availability of resources. Given the unexpected importance of invertebrate-derived prey, including some of terrestrial origin (i.e. aerial or semi-aquatic insects), during the freshwater phase of the M. capensis life cycle, we also emphasize a need for a re-assessment of the trophic designation of this species (previously designated as a strict detritivore).
KeywordsFish trophic ecology Insects Allochthony Detritivory Ontogeny Riparian zone
This study was funded by the Water Research Commission (WRC) of South Africa, the National Research Foundation (NRF) of South Africa, Rhodes University’s Sandisa Imbewu Initiative, and the South African Institute for Aquatic Biodiversity (SAIAB). This project received ethics clearance from Rhodes University (RU Ethics Clearance ZOOL-02-2012) and the South African Institute for Aquatic Biodiversity (SAIAB Ethics Clearance 2012/04). We thank Paul Cowley, Mandla Magoro, Tatenda Dalu, Leandro Bergamino and Bernadette Hubbart for their assistance with field and/or laboratory work.
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