The Biology and Culture of Tilapias

oxygen supersaturation (up to 400% in Lake Chilwa, Morgan 1972). Super-
saturation of dissolved gases (oxygen and also nitrogen) often poses problems
in the intensive rearing of tilapias in industrial heated effluents (MQlard and
Philippart 1980).

OTHER FACTORS

Tilapias tolerate high turbidities and are rather resistant to pollutian by

toxic substances, whether organic or inorganic, natural or artificial (e.g.,

pesticides, see Balarin and Hatton 1979).

Feeding Behavior

Tilapias of the genus Tilapia, especially T. rendalli, T. zillii, T. sparrmanii

and T. tholloni are macrophyte-feeders in which the adults feed preferentially

on filamentous algae, aquatic macrophytes and vegetable matter of terrestrial

origin (leaves, plants, etc.); but this specialization does not exclude certain

stages of development (alevins) at certain times of year (winter), and in

certain waters poor in aquatic vegetation, taking animal food (here including

the alevins) as shown by Spataru (1978) for T. zillii in Lake Kinneret (Israel).

In this lake, T. zillii also eats blue-green algae.

In the genus Sarotherodon, certain species (often endemic lacustrine

species) seem very specialized feeders, notably S. variabilis of Lake Victoria

(fine benthic sediments, Fryer and Iles 1972), S. alcalicus grahami of Lake

Magadi (epilithic blue-green algae), S. esculentus (phytoplankton) and S.

macrochir (phytoplankton and epilithic algae). But many species have a

much more diversified feeding regime with a dominant vegetable component

(epilithic, epiphytic and filamentous algae, phytoplankton, vegetable debris

and fine sediments rich in diatoms and bacteria) and an animal component

(zooplankton and benthic organisms such as insect larvae, crustaceans,

molluscs). S. aureus (Spataru and Zorn 1978), S. galilaeus (Lauzanne and

Iltis 1975) and S. niloticus (Moriarty 1973) eat blue-green algae. Moriarty

and Moriarty (1973a) have demonstrated that S. niloticus can assimilate 70 to

80% of the carbon ingested in this form (Microcystis, Anabaena and Nitzchia).

S. aureus (Spataru and Zorn 1978), S. shiranus chilwae (Bourn 1974) and S.

mossambicus (Bruton and Boltt 1975; Man and Hodgkiss 197713) are equally

able to eat vegetable debris and macrophytes. In certain waters S. mossam-

bias even catches terrestrial insects floating on the water surface and fish

(Lake Sibaya, Bruton and Boltt 1975).

S. andersonii, S. aureus, S. mossambicus and S. niloticus appear to be

omnivorous compared to S. galilaeus and S. macrochir which have a much

more limited food spectrum. Studies made in Lake Kinneret, Israel (Spataru

1976; Spataru and Zorn 1978) show that feeding is much more selective in

S. galilaeus (Pyrrophytes, Peridinium sp.) than in S. aureus (zooplankton,

while this is abundant; phytoplankton and vegetable debris, when the

zooplankton is less abundant).