Article

Trophic ecology and persistence of invasive silver carp Hypophthalmichthys molitrix in an oligotrophic South African impoundment

Published in: African Journal of Aquatic Science
Volume 41, issue 4, 2016, pages: 399–411
DOI: 10.2989/16085914.2016.1246356
Author(s): N LübckerDepartment of Zoology and Entomology, South Africa, J DabrowskiDepartment of Zoology and Entomology, South Africa, TA ZengeyaDepartment of Zoology and Entomology, South Africa, PJ OberholsterCouncil for Scientific and Industrial Research (CSIR), South Africa, G HallSouth Africa Stable Isotope Laboratory, South Africa, S WoodborneSouth Africa Stable Isotope Laboratory, South Africa, MP RobertsonCentre for Invasion Biology, Department of Zoology and Entomology, South Africa

Abstract

The alien invasive silver carp Hypophthalmichthys molitrix established a self-sustaining feral population in an oligotrophic impoundment, Flag Boshielo Dam, in South Africa. The ability of this population to persist in a dam with low algal biomass (median annual suspended chlorophyll a = 0.08 µg l−1), and limited access to rivers considered large enough for successful spawning, has implications for their invasive potential in other systems. Stomach content and stable isotope analysis were used to assess the trophic ecology of H. molitrix, which was then compared with indigenous Mozambique tilapia Oreochromis mossambicus, on a seasonal basis during 2011. Hypophthalmichthys molitrix are generalist filter feeders, with a diet consisting primarily of sediment, vegetative detritus, dinoflagellates and diatoms. The dominance of sediments in their stomachs suggests occasional benthic scavenging. However, H. molitrix occupied a higher trophic level (TL = 2.8) than expected, suggesting that this population subsidised their diet with an unidentified dietary constituent, characterised by enriched nitrogen values. Although the stomach contents indicated dietary overlap between H. molitrix and O. mossambicus, stable isotopes revealed fine-scale resource partitioning, despite both species occupying the same trophic level. Nonetheless, the persistence of this feral H. molitrix population in an oligotrophic impoundment highlights their phenotypic plasticity.

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