SEASONAL DEVELOPMENTAL CAHNGES IN THE OVARIES OF SIGANUS RIVULATUS FROM THE RED SEA

SEASONAL DEVELOPMENTAL CAHNGES IN THE OVARIES

OF SIGANUS RIVULATUS FROM THE RED SEA

EKRAM MOHAMED AMIN

Institute of Oceanography and Fisheries, Alexandria, Egypt.

ABSTRACT
The annual sexual cycle of the ovary of female S.
rivulatus throughout its I ife in the Red Sea can be divided
into two promi nent oocyte growth peri ods. The growth peri od
is less active and it includes the mitotic division of
reserved oogon i a, syanpsisand protop Iasmi c growth of
oocytes. The comprehens i ve changes occur in the seconda ry
growth period. This highly active period is characterized
by a dense deposition of yolk giving rise to a large size
of oocyte. The different 1ayers formi ng the egg membrane
are well developed. The nucleus with its contents
(Karyop Iasm) are subjected to many consecuti ve changes
so as to receive the spermatozoa through the micropyle
which is well developed in the transition stage of gonad
maturation (IV-V) in the animal pole. The active period
of gonad development takes about three months (JanuaryMarch). Female begins to spawn in March (average diameter
eggs are 0.48 .!. 0.015 nrn) once a season, hence S. rivulatus
is a monocyclic fish. Spawning season in the Red Sea extends
to about seven months (March-September) during which fishes
with ripe ovaries appear in the catch. Other fishes with
spent ovaries show the process of atresia where the residual
eggs and groups of empty follicle layers are detected.