HORMONAL INDUCTION OF OOCYTE FINAL MATURATION AND OVULATION IN THIN-LIPPED GREY MULLET, LIZA RAMADA (Risso)

HORMONAL INDUCTION OF OOCYTE FINAL

MATURATION AND OVULATION IN THIN-LIPPED GREY

MULLET, LIZA RAMADA (Risso)

By
MQSTAFA A. MODSA*
*National Institute ofOceanography and fisheries, Alexant{ria.
Key words: Oocyte, maturation, ovulation, immunocytochemistry,
pituitary gland, Liza ramada (Teleostei).
ABSTRACT
The application ofa high potency synthetic analogue ofluteinizing .
hormone-releasing hormone (LHRH-a) in combination with human
chorionic gonadotropin (BCG) for inducing the final stages of
maturation and ovulation in the grey mullet Liza rllllUUla was
investigated in prespawningfemales, with average egg diameters of
600 I.lm or more, by three hormonal injection strategies. The average
GSI and diameter of ovarian oocytes increased graduaDy during
induction of final oocyte maturation (pOM). Mature and transparent
oocytes (mean diameter was 900 -T- 50 I.lm) were observedin about
85% of the stimulated females; however, ovulation occurred only in
35% ofinjectedfemales.
. Final oocyte maturation (POM) of fish treated with lHRH-a in
combination with HCG showed two phases: early phase associated
with lipid-droplet coalescence andgerminal vesicle (GV) migration,
and late phase included germinal vesicle breakdown (GVBD) and
yolk-globule coalescence. Translucent ovulated eggs had completely
coalesced ,lipid and yolk masses. The changes in the activity of
gonadotropin (GTH), somatolactin (SL), adrenocorticotropin (ACIH)
and melanin-stimulating hormone (MSH)-secreting cells associated
with hormonal-induced FOM ‘were studied immunocytochemically.
Early FOM was associated with high synthetic activity ofthe GTH,