Other cichlids in Lake Bosumtwi are Chromidotilapia guentheri, a benthos
feeder in which the juveniles take the same food sources as the adults,
and Hemichromis fasciatus, the juveniles of which share the allochthonous
fauna at the lake surface with juvenile tilapia, as do the juveniles of the
catfish Heterobranchus isopterus. Adult Hemichromis fasciatus and Hetero-
branchus isopterus are both piscivorous, eating juvenile tilapias. Once the
tilapias reach a certain size they are relativ 4 ly safe from predation.
The breeding places and habits of these three tilapias also segregate
them. Most S. g. multifasciatus spawn between November and April (though
Fome ripe fish may be found at any time of year). Nests are made at 1 to 3 m
in the littoral zone over a sandy substrate, among reed beds (Typha australis)
or in openwater; eggs are brooded by both parents and brooding fish may be
found 5 to 20 m from shore. Of the two Tilapia species, T. discolor has a
protracted breeding season from Deceniber to May, making nests with
axillary pits at 1 to 7 m in the littoral zone over muddy bottoms (240 to 700
eggs per nest). T. busumana peaks from Qctober to February (though some
are ripe at any time of year), making a bdwl nest in permanent streams and
the littoral zone over sandy or stony shores in 10 cm to 1 m water (60 to
280 eggs per nest). The nests are of very different form: the T. busumana
nest is a simple bowl; the T. discolor nest has axillary pits around the main
nest. These tilapias do not seem to grow vew large.
In west Cameroons the oligotrophic Lake Barombi Mbo has four endemic
species of Sarotherodon, of which two species, the galilaeus-like S. steinbachi
and S. loh bergeri share organic debris obtained in shallow water, from sandy
areas by S. steinbachi and aufwuchs sucked off rocks by S. lohbergeri. Both
species also probably take some food when skittering at the surface (Green
et al. 1973). The other two species (S. linelli and S. caroli probably related
to the S. melanotheron group) share phytoplankton-feeding a meter or so
below the lake surface; possibly differenc s in breeding seasons help to keep
these two species apart (Trewavas et al. 19 f 2). Another Cameroon crater lake,
Lake Kotto is eutrophic with a dense bloodn of blue-green algae, food of three
tilapias, S. galilaeus, T. mariae and the endemic T. kottae. The two Tilapia
species both take some bottom food (invertebrates in T. kottae) as well. This
lake lacks the aufwuchs-feeding niche fqund in the oligotrophic Barombi
Mbo. The phytoplankton eaten by adults is so abundant in Lake Kotto that
tilapia numbers are more likely to be limited by availability of food and
feeding habitats for the young stages whiqh live and feed inshore (Corbet et
al. 1973).
Lake Magadi in the Kenya rift, a very alkaline lake (pH 10.5), with hot
springs (43"C), and a high specific gravity (1.01 to 1.03) is inhabited by a
little Sarotherodon, S. alcalicusgrahami (fotmerly known ass. grahami) whose
ecology and behavior was studied by Cbe (1966). These fish browse on
blue-green algae on the stony bottom, with small crustaceans
(copepods), and dipteran larvae, in the w near the hot springs,
moving into deeper water at night when begins to