| dc.description.abstract | Histological and seasonal changes in the gonadal
development and the biology of the cat-fish Clarias
mossambicus (Peters), in the Nyanza Gulf of Lake
Victoria were studied during a period of twelve months.
In the females, germ cells proliferatte through
mitotic divisions and become transformed into oocytes.
Growth of oocytes as a result of synthesis of
protoplasmic, and then trophic substances, eventually
result in maturation. In the males,maturation is
brought about as a result of a series of divisions of
the germ cells giving rise, through intermediate stages,
to ripe spermatozoa.
Anaysis of the seasonal trends in the gonadosomatic
index (GSI), changes in histological conditions and
variations in the percentage occurrence of different
maturity stages of the gonads reveal that the peak
breeding ativity of the fish is confined to be time
of maximum,rainfall in the months of March, April
and May, and extend up to June
The flood-plains, swamps and temporary streams
and rivers draining into the gulf were identified
as the spawning grounds of the species, and, during
the breeding time, the species undertook spawning migration
to these areas.
Six maturity stages were identified in the females and
five in the males.
The minimum size at sexual maturity was in the size
range of 40-45 cm in both the males and females.
The females dominated over the males in the
population just before the breeding season (in February)
and immediately after the peak breeding time (in May). During
the peak breeding period, however, the sex ratio was 1:1.
The males then dominated over the females during the rest of
the period
Fecundity estimates for 27 females ranged from
7,966 eggs to 229,648 eggs in fishes measuring 46.0 cm
and 87.0 cm respectively, with a mean of 78,152 eggs.
There was a positive linear relationship between fecundity
and (i) total length (r,~ 0.92; P < 0.001) (ii) body
weight (r =,0~~4;'P < 0.001) and (iii) ovary weight
(r = 0.~9·; p < 0.001) .. The regression equations for
these relationships are described.
From logarithmic equations describing the
length-weight relationships, it seems that growth in
the species is isometric.
The relative condition was generally high and
both males and females reached maximum condition
just Prior to spawning. | en |
