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Abstract
Possible reasons why Oreochromis niloticus have supplanted Oreochromis macrochir as the main commercial fish species in Lake Chivero, Zimbabwe, were investigated in 2006. Diel feeding trends, daily food consumption and protein digestion efficiencies of the two species were compared. Both followed a similar diurnal feeding trend, with peaks at 12:00 and 16:00. The stomach content dry weight for large fish of 20–30 cm SL peaked in the morning, whereas for small 10–20 cm SL fish it peaked at dusk. Small O. niloticus and O. macrochir fed for 14 h and 12 h, respectively, whereas big fish fed on average for 8 h and 6 h, respectively. Oreochromis macrochir ingested more food than O. niloticus. Small Oreochromis macrochir ingested 2.7 g d−1, which was 53% more than that ingested by O. niloticus of comparable size. Big O. macrochir also ingested 2.7 g d−1, which was 4% more than that of O. niloticus of comparable size. The mean digestive coefficient of proteins ingested by O. niloticus, 62.5% (SD 8.6), was higher than that of O. macrochir, 39.4% (SD 9.1). The efficiency of O. niloticus in utilising food was identified as one of the possible reasons why it had successfully replaced O. macrochir in Lake Chivero.