NATURAL
REPRODUCTION
C. gariepinus shows
a seasonal gonadal maturation which is usually associated with the rainy
season. Research carried out by Graaf and his team in 1995 shows that
maturation processes of C. gariepinus are
influenced by annual changes in water temperature and photoperiodicity and the
final triggering of spawning is caused by a rise in water level due to
rainfall. An instance of maturation and spawning of C. gariepinus in Lake Victoria (Kenyua) is presented in Figure 5.1;
reproduction starting in March just after the start of the first heavy rains as
is indicated by the decrease in the Gonad. Somatic Index1 (G.S.I.) Natural
reproduction is completed in July and the G.S.I. remains low till November,
thereafter the oocytes start maturing gradually and become ripe again in March.
GSI = {weight of ovary / total
weight} x 100
Spawning
usually takes place at night in the shallow inundate areas of the rives lakes
and streams. Courtship and mating takes place in shallow waters between
isolated pairs of males and females. The mating posture, a form of amplexus
(the male lies in a U shape curved around the head of the female) is held for
several seconds. A batch of milt and eggs over a wide area. The pair usually
rest after mating (from seconds up to several minutes) and then resume mating.
There is no parental care for ensuring the survival of the catfish offspring
except by the careful choice of a suitable site. Development of eggs and larvae
is rapid and the larvae are capable of swimming within 48-72 hours after
fertilization at 23-280c.
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