debris and phytoplankton, which seems on the whole to be ingested passively
rather than sought actively. S. galilaeus feeds much more selectively (phyto-
plankton: Pyrrophytes, Peridinium sp.) and its feeding regime has a less great
seasonal variation, in accordance with the availability of its food. T. zillii
feeds mainly on Coleoptera and chironomid pupae plus green, brown and
above all red algae (Peridinium sp.) in winter and spring and on zooplankton
(Cladocera) in summer and autumn (Spataru 1978). While breeding, T. zillii
modifies its feeding habits and captures benthic prey normally not eaten at
other times of year.
In Plover Cove Reservoir, Hong Kong, S. mossambicus feeds almost
exclusively on mud and vegetable debris (more than 80% by volume) through-
out the year, without appearing to have any seasonal cycle.
According to Man and Hodgkiss (1977b), in Plover Cove Reservoir, Hong
Kong, S. mossam bicus feeds during the day. The feeding intensity (measured
by an index of stomach fullness) is maximal between 12:00 P.M. and 3:00 P.M.
and then slows progressively so that stomachs are completely empty between
12:OO A.M. and 3:00 A.M. Diurnal feeding has also been observed in S. shi- j
ranus chilwae (Bourn 1974), S. alcalicus grahami (Coe 1966, 1967), S.
niloticus in Lake George (Moriarty 1973) and T. busumana in Lake Bosum-
twi (Whyte 1975), but several other species are nocturnal feeders, notably
T. discolor and S. multifasciatus of Lake Bosumtwi (Whyte 1975).
Tilapia feeding activity varies seasonally according to various factors:
temperature, reproduction, interspecific competition. In Plover Cove Re-
servoir, Hong Kong, the seasonal cycle of feeding activity follows the tem-
perature cycle: minimum activity in January-February (16 to 17°C) and
maximum in July-September (27 to 30°C). In Lake Kinneret, Israel (Spataru
and Zorn 1978), the feeding activity of S. aureus (measured by index of
stomach fullness) is maximal in summer and autumn (temperature maximal,
30°C) whereas that of T. zillii is maximal in spring and relatively constant at
other seasons (Spataru 1978).
Feeding activity is not interrupted while guarding the young in substrate-
spawners (for example T. zillii, Spataru 1978) but normally stops in mouth-
brooding females, though not always, because food has been found in the
stomach of a mouthbrooding female of S. alcalicus grahami (Coe 1966, in
Fryer and Iles 1972, p. 124).Reproductive BehaviorNumerous authors have studied tilapia breeding behavior in the laboratory,
in culture systems and in the field. The following notable references are not
an exhaustive list:
S. esculentus (Cridland 1961)