The Biology and Culture of Tilapias

reproduction during part of the year, the length of time depending on the
latitude and altitude of the place: the duration of the breeding season then
conditions the number of spawnings a year, and consequently the overall
fecundity of the populations. The breeding seasons coincide with the hottest
times of year (T. zillii of Lake Qarun, Egypt, S. mossambicus of Lake
Sibaya) sometimes just before the rainy season (S. mortimeri in the Zarnbezi
River and S. macrochir and T. rendalli in Shaba).
Table 6. Data on the periodicity of reproduction of some tilapia species in natural waters
at different latitudes and altitudes.

Coastal Lake Sibaya (S. Africa) 27'25's

The breeding season of S. mossambicus starts in September (20-26OC) and is prolonged

until March (duration: 7 months) but the maximum activity is concentrated in September-

December; a complete cycle of reproduction lasts about 7 weeks (20 to 22 days for

incubation of embryos and guarding the young and about 14 days for the maturation of

ovules); the same female should therefore theoretically reproduce 3 to 4 times per year

(Bruton and Boltt 1975).

The man-made Lake McIlwaine (Zimbabwe) 18'5

The breeding season of S. macrochir (introduced) lasts principally from September to

December, that is to say during the hottest months of the year, just before the rainy

season; but a rise in lake level later in the year (January-March) is able to stimulate a

second phase of reproduction (Marshall 197913).

Middle Zambezi 15-18's

The short breeding season (one or more spawnings) of S. mortimeri coincides with the

rainy season (Fryer and nes 1972).

The man-made Lake Lufira (Shaba, ZaTre) lloS, 1,100 m

S. macrochir and T. rendalli reproduce throughout the year but there is a very slight

slowing down of reproduction during the cold dry season (MayJuly) and an intense

activity in the rainy season (Ruwet 1962); observations made in fish culture in the same

region (De Bont 1950), showed that the duration of the rainy season determines the

number of spawnings (3 to 4 per year at intervals of 7 weeks in T. rendalli).

Lake Malawi 9°30'-14040'~, 471 m

S. saka, S. squamipinnis and S. lidole produce only one spawning a year; S. saka breeds

during the hot season (August-November) before the rainy season, S, squamipinnis during

the rainy season (December-April) and S. lidole in October-November, just before the

rainy season (Lowe 1952; Fryer and nes 1972). Apart from the rains, the temperature

conditions and photoperiodicity vary relatively little through the year.

Lake Naivasha (Kenya) 0°46's, 1,890 m

The photoperiod is practically constant (12 h) and the temperature favorable throughout

the year. Reproduction of S. leucostictus (introduced) is continuous (nonseasonal) and

one cannot observe any correlation between its intensity and the seasonal precipitations

(Siddiqui 197713). Previously another author (Hyder 1970a) had concluded that a seasonal

reproduction was correlated with certain conditions of temperature and light intensity.

The observations of Siddiqui (1979a) indicated that T. zillii (introduced) reproduced

equally throughout the year, with little seasonal variation in the intensity of reproduction.