MFSc

Sex pheromones are reported to be present in many crustaceans which
mostly have releaser effect on sexual behaviour. The discovery of a male (primer)
pheromone with stimulatory effect on ovarian maturation and ovulation has added
an important external factor to the basic mechanisms regulating reproduction in
fresh water prawns. But studies in these lines are very few in the economically
important species of Macrobrachium. Knowledge about this male pheromone
will be useful to help or potentiate reproduction and/or extend the breeding period
of freshwater prawns, which are of great aquacuItural importance.
The present study was carried out in the slender nver prawn,
Macrobrachium idella. Seven ovarian maturity stages have been distinguished
here. Histological studies of the maturing oocytes helped to understand the
changes taking place during oocyte growth and maturation through the
progressive maturity stages. Yolk vesicles start appearing in the cytoplasm of
oocyte in maturity stage II which is the beginning of vitellogeneis (vitellogenesis
I). In stage IV, yolk platelet synthesis starts and 'a peripheral layer of yolk
platelets appear in this stage. Later these yolk platelets completely fill the ooplasm
through stages V and VI when the ova increase in size enormously. Gonado-
somatic index (ovarian index) of different maturity stages was determined and
was found useful to differentiate especially the late maturity stages. Ova diameter
studies along with the other observations showed a clear picture of protracted
multiple spawning in this species with batches of ova undergoing maturation and
ovulation in successive maturation cycles.

When the females were reared in isolated condition, their ovarian growth
was found to be arrested at early stage IV. This restriction of ovarian maturation
was found mostly in the second maturation (gonadal) cycle after isolation. But
those isolated females which had a common water circulation with males showed
normal ovarian maturation and ovulation. Therefore, it can be concluded that a
male pheromone exists in this species which is essential for normal ovarian
growth and maturation. Another experiment was conducted to find out the tissue
source of this putative male pheromone. When these isolated females were
exposed to extracts of testis, vas deferens or muscle, both testis and vas deferens
extracts were found to stimulate the ovarian maturation and ovulation in isolated
females, while the muscle extract (control) was ineffective. This shows that in M
idella, the male pheromone is produced by testis and vas deferens or it is
produced by testis and transported to vas deferens.
Further experiment showed that charcoal extraction destroys the
pheromonal activity in testis and vas deferens extract while boiling has no such
effect which indicates that the ovary stimulating pehromone in M idella may be a
steroidal molecule as reported in some fishes.