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Piscivory does not cause pansteatitis (yellow fat disease) in O reochromis mossambicus from an A frican subtropical reservoir
Author(s) -
Dabrowski J.,
Hall G.,
Lübcker N.,
Oberholster P. J.,
Phillips D. L.,
Woodborne S.
Publication year - 2014
Publication title -
freshwater biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.297
H-Index - 156
eISSN - 1365-2427
pISSN - 0046-5070
DOI - 10.1111/fwb.12360
Subject(s) - biology , detritus , population , oreochromis mossambicus , omnivore , zooplankton , zoology , ecology , fishery , tilapia , fish <actinopterygii> , demography , sociology , predation
SummaryPansteatitis (yellow fat disease) is ubiquitous in the free‐ranging population of Oreochromis mossambicus from Loskop Reservoir ( LR ), South Africa. The disease is nutritionally mediated and associated with a diet high in polyunsaturated or rancid fats, frequently of fish origin. While piscivory has never been reported in dietary studies of O. mossambicus in their native range, their opportunistic and omnivorous feeding habits mean that piscivory cannot be ruled out as a cause of the disease. The diet of O. mossambicus from LR ( n = 91) was compared with a population from Flag Boshielo Reservoir ( FBR ; n = 81) located <100 km downstream, where no pansteatitis occurs. The stomach contents and stable isotope signatures (δ 15 N and δ 13 C) of fish and food sources were evaluated across four seasons. Isotope signatures were also compared over various time scales from historic samples and mortalities collected from LR . There was no evidence of piscivorous feeding behaviour in fish from either location or from historic LR samples. The results of the stable isotope analysis in R mixing model and stomach contents analysis showed that the dinoflagellate, Ceratium hirundinella , was the dominant food source followed by zooplankton, detritus and Microcystis aeruginosa in LR . The diet of fish from FBR was less diverse than fish from LR and was dominated by sediment and detritus. The distinguishing feature of the dietary comparison between reservoirs was the abundance of planktonic food items dominated by C. hirundinella in the diet of fish from LR . The lack of evidence for piscivory among O. mossambicus from LR suggests that the classic aetiology of pansteatitis does not apply. This highlights the need to further explore direct (environmental exposure to pollutants) and indirect (dietary exposure) links to pansteatitis. This study identified the major dietary constituents for O. mossambicus , which enables future research to focus on their nutritional and chemical composition.