adults do not feed in the shallows are discussed elsewhere (Bowen 197613;
Bruton 1979). With regard to the food quality problem, the important
findings of the Lake Sibaya study are: 1) food quality varies significantly
between and according to a predictable pattern and 2) juvenile S. mossam-
bicus risk the perils of the near-shore shallows (predators, heavy-wave action)
to utilize selectively food of the highest available quality.
Similar results were obtained in a study of S. mossambicus adults in
Lake Valencia, Venezuela (Bowen 1980a, 1980b, 1981). These fish fed on
periphytic detrital aggregate attached to Potamogeton spp. The protein
content of this food resource varied from site to site and was directly pro-
portional to the slope of the littoral zone bottom. Adult S. mossambicus fed
selectively in the steeply sloped littoral zone (Figure 4). Some difficulty
arose in interpretation of these results because assimilated protein:assimi-
lated energy ratios indicated that protein levels were too low to support
growth, but the fish were in excellent condition and reached a large maximum
size. Further study revealed that in addition to protein, the diet contained
detrital amino acids bound into the amorphous detritus. Detrital amino acids
were most abundant in the steeply sloped littoral zone where the fish feed
(Figure 5) and were assimilated with an efficiency of 64%. With this source
of amino acids taken into consideration, adult S. mossambicus in Lake
Valencia assimilated the equivalent of 14.4 mg of protein per kJ of assimilated
food energy: an amount expected to produce good growth. As with the Lake
Sibaya study, these results show S. mossambicus in Lake Valencia selected
high quality food that maximized growth.
Littoral zone slopeFigure 4. Habitat partitioning by male and female Sarotherodon mossambicus in Lake
Valencia, Venezuela. Males in breeding coloration build nests and defend territories in the
gently sloped littoral while females and non-breeding males feed in steeply sloped littoral
where food quality is highest. Lines fitted by least-squares. (Reproduced by permission of
the Ecological Society of America.)