Feeding and Grazing in Lake George, Uganda

• Published in: Proceedings of the Royal Society of London. Series B, Biological sciences Biological sciences, 1973-12, Vol.184 (1076), p.299-319
• Main Authors: Moriarty, D. J. W., Johanna P. E. C. Darlington, Dunn, I. G., Moriarty, Christine M., Tevlin, M. P.
• Format: Article
• Language: English
• Subjects: Algae; Carbon; Fish; Freshwater fishes; Herbivorous fishes; Ingestion; Insect larvae; Phytoplankton; Stomach; Tilapia
• ISSN: 0962-8452; 0080-4649; 1471-2954; 2053-9193
• DOI: 10.1098/rspb.1973.0050

The fauna of Lake George is dominated by herbivores, in particular the fish Tilapia nilotica and Haplochromis nigripinnis, and the cyclopoid copepod Thermocyclops hyalinus. Digestion, and the assimilation of carbon from algae, by these herbivores were studied in detail. It was found that, contrary to previous observations reported in the literature, both fish and zooplankton were able to digest and assimilate blue-green algae. The diurnal feeding patterns of the herbivores were examined, and methods devised for assessing, in terms of carbon, the daily ingestion of algae. Hence, using biomass data, the total amount grazed by the herbivores was calculated. Estimates of carbon requirements at other trophic levels were made, as was an assessment of the required level of net production by the algae for comparison with figures for standing crop and net algal production measured by other means. Food selection by secondary and tertiary producers is discussed, and in several species age correlated changes in selectivity were examined. Both the major herbivorous species of fish adopt phytoplankton feeding after a period of carnivorous or omnivorous feeding as fry. Thermocyclops hyalinus is herbivorous all its life, but the size of particle taken changes with age. There are more species of carnivorous than herbivorous fish and these exploit a wider variety of food sources; the few species studied also show changes in food preference with age.