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Abstract
The life histories of five populations of moggel, Labeo umbratus, inhabiting small Eastern Cape reservoirs were compared and the differences related to environmental parameters. A significant positive correlation between fish growth and chlorophyll a was noted in four cases. In the eutrophic Dimbaza Reservoir, slow growth rate was attributed to intraspecific competition. Mortality was lower in populations living amongst fewer predatory species, and also where food was abundant. Length- and age-at-maturity were not affected by environmental factors, but were dependent on growth and mortality. There was a weak relationship between the fishery potential of L. umbratus populations and algal biomass, and thus it was concluded that populations in small, shallow, slightly enriched reservoirs would be those more suitable for exploitation.