The Biology and Culture of Tilapias

Table 6 (cont'd)
Lake Victoria 03~00'S-0~20'N, 1,136 m

Fryer (1961a) indicated that the reproduction of S. variabilis is continuous but there are

seasonal variations in intensity which are not clearly correlated with climatic conditions

(rains and temperature); there are at least three spawnings in a period of eight months. In

S. esculentus, there exists a correlation between the rainy season and the periodicity of

reproduction (Garrod 1959, cited by Fryer and Iles 1972); Welcomme (1967b) reported

two reproductions or more a year.

Lake Bosumtwi (Ghana) 06~30'N, 1,070 m

The endemic tilapias of this lake breed throughout the year but the reproductive activity

is maximal at a determined period of year: October-February (T. busumana), November-

April (S. mu2tifasciatus), December-May (T. discolor) (Whyte 1975).

Lake Moyua (Nicaragua) 12'35'N, 420 m

S. mossambicus (introduced) reproduces during 5-6 months correspond,ing to the rainy

season (Reidel 1965).

Plover Cove Reservoir (Hong Kong)

S. mossambicus (introduced) is here at the extreme northern limit of its range for reason

of temperature conditions (less than 20°C and practically without growth during 3 to 4

winter months); the breeding season extends from May to October and the same female

lays at least twice per year (Hodgkiis and Man 1978).

Lake Qarun (Egypt) 2g029'N, 45 m

The breeding season of T. zillii coincides with the hottest months, May-November (El-

Zarka 1956, cited by Siddiqui 1979a).

CHOICE OF SPAWNING GROUNDS, TERRITORIALITY,

SPAWNING AND GUARDING THE YOUNG

In the substrate-spawners the mature males first billet themselves for

nesting along the shores where each delimits and defends a territory on the

bottom; the females join them and after a fairly long courtship of several

hours to some days, the couples are formed. The two partners participate

in preparing a nest by digging holes of varying depth some of which may

shelter an adult (De Bont 1950; Daget 1952; Ruwet 1962). In the Lufira

reservoir (Ruwet 1962) T. rendalli established its territories at a depth of

20 to 80 cm (especially 50 cm) preferentially on ground with a marked

slope and near to the marginal fringe of vegetation; the territories, which

attain one meter diameter, may be adjoining, giving the impression of true

colonies. In Lake Kinneret, Israel, T. zillii prefers bottoms with pebbles or

sand with abundant vegetation (Phmgrnites); the territories are smaller

(2.0 to 2.5 m2) in habitats with dense vegetation than in open water (5 to

6 m2) (obstructing vision curbs aggression by restricting the sight of neigh-

bors) (Fishelson 1966a, 196613).

Oviposition and fertilization are long operations: males and females

alternately apply the genital papilla to the bottom, at the side of a hole,