Journal
JOURNAL OF FISH BIOLOGY
Volume 73, Issue 3, Pages 477-497Publisher
WILEY
DOI: 10.1111/j.1095-8649.2008.01920.x
Keywords
biomagnification; diet shifts; mercury; piscivory; stable isotopes
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The diet, habitat use and mercury concentration of the small fish species, the straight fin barb Barbus paludinosus, were studied in Lake Awassa, Ethiopia, for a period of 1 year from February 2003 to January 2004. Stable isotope signatures of nitrogen and carbon in different total length (L-T) classes were used to determine trophic positions and organic carbon sources, respectively. Barbus paludinosus mainly occupied the protected benthic habitats (littoral and profundal) of the lake. The delta C-13 values were in the range from -24 to -19 parts per thousand, indicating that the carbon source for B. paludinosus was benthic, as well. Small individuals (<= 60 mm L-T) mainly preyed upon ostracods, intermediate sizes (60-100 mm) on aquatic insects and gastropods, while a tiny cyprinodont fish Aplocheilichthys antinorii dominated the diet of large individuals (100-160 mm). The progressively increase in delta N-15 with increasing L-T also indicated a diet shift towards piscivory in larger individuals. The mercury concentration ranging from 0.02 to 0.74 mg kg(-1) wet mass (wm), was unexpectedly high in this small species, and was significantly positively related to L-T, as well as to delta N-15. Some large individuals had mercury concentrations < 0.1 mg kg(-1) wm, and low delta N-15, indicating substantial variations in diet between individuals of same size. The study suggests that other piscivorous species which include B. paludinosus in their diet may have a high mercury intake risk. (C) 2008 The Authors Journal compilation (C) 2008 The Fisheries Society of the British Isles.
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