the one depositing a batch of eggs, the other covering them with milt, and
the application forms a plaque of spawn composed of several thousand eggs
stuck to the bottom.
Males and females then guard the eggs, and ventilate them with the aid
of their fins. After hatching, they move the alevins frequently from one
hole to another. As soon as they know how to swim, the alevins organize
themselves into a cloud which stays in the immediate neighborhood of the
nest and retreats into a hole in time of danger. They are constantly regrouped
by the jolting movements, accentuated by contrasting colors, of one parent
while the other mounts guard at the boundary of the territory (Voss and
Ruwet 1966). After 2 to 3 weeks, the alevins leave the territory and the
parents are able to recommence spawning.
In mouthbrooders, the males remain in the nesting zones. Each carrying
a marked, often brilliant, color, delimits and defends a territory and makes
a nest where he tries to attract and retain a female (Lowe-McConnell1959).
The organization of the breeding arenas varies. In Lake Victoria and the
Malagarasi swamps the arenas of S. variabilis and S. karomo observed by
Lowe-McConnell (1956a, 1959) were situated in open water, on a sandy
bottom, at a depth of 0.15 to 1.0 m (S. variabilis) and 0.5 to 1.5 m (S.
karomo). In the Lufira reservoir (Ruwet 1962) S. macrochir nest at a depth
of 0.8 m to 1.5 m (mode, 1.2 to 1.3 m) on a flat bottom, devoid of vegetable
debris from the beaches, and on high alluvial banks situated towards the
open water. In Lake McIlwaine, the areas of S. macrochir are established in
shallow water but certain nests are made exceptionally up to 5 m deep
(Marshall 1979b). Bruton and Boltt (1975) have studied in detail (mainly
by diving) the distribution and the characteristics of S. mossambicus nests
in Lake Sibaya, according to type of habitat, depth and vegetation. Most of
the nests are established at the edge of the littoral terrace, just before the
steep slope. The nests are situated at a depth of 0.4 to 8.5 m but with a
maximum concentration between 0.5 and 5.0 m; the size of the nest in-
creases with depth; they are associated with scattered vegetation of medium
density, composed mainly of Scirpus sp. and Potamogeton sp.
The females make only brief visits onto the arenas. Passing from one
territory to another, they are courted by several successive males, until the
moment when, stopping in front of a nest basin, a female deposits a batch
of eggs, the male fertilizes them immediately and the female takes them
in her mouth to brood them. The operation is very brief (50 to 60 seconds)
and may be repeated with the same male, or with another in a neighboring
territory (successive polygyny and polyandry, Ruwet 196313). Finally, the
female leaves the arena, where the males stay billeted, and she carries several
hundred eggs in her mouth (see Balarin and Hatton 1979) which she broods,
staying in a zone sheltered with vegetation (brooding area) described by
Bruton and Boltt (1975) for S. mossambicus. As soon as the yolk sac is
resorbed (see Table 7) the female lets the alevins escape from her mouth.
They form a cloud which orientates itself constantly in contact with the
mother, following her slow movements and taking refuge in her mouth at the
least sign of danger, warned by her movements (see Voss and Ruwet 1966).
When the alevins reach a certain size (9 to 10 mm in S. mossambicus, Bruton
and Boltt, 1975) the females leave the brooding areas and sometimes gather
sean pound
(Sean Pound)
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