Histological and immunohistochemical investigation on ovarian development and plasma estradiol levels in the Swordfish (Xiphias gladius L.)

The paper reports a histological and immunohistochemical
description of oocyte growth and ultrastructural aspects of
zona radiata (ZR) formation as well as the relationship
between plasma estradiol-17b‚ (E2) levels and ovarian
development in swordfish (Xiphias gladius L.) from the
Mediterranean Sea. Ovaries were inactive during March to
mid April; maturation occurred during late April to June and
spawning in June and July.
Zona radiata formation starts, as Pas positive material, in
oocytes at the lipid stage. In this stage a deposit of electrondense
material between oolemma and follicular cells
appears. In the cortical alveoli stage and through the early
vitellogenic stage, the deposition of a moderately electrondense
material occurred on the inner side of the ZR. Finally,
in late vitellogenic oocytes a third layer, made of microfibrillar
material, appeared. The immunohistochemical analyses
revealed that the initial internalisation of hepatic zona radiata
proteins (Zrp) in the swordfish oocyte starts before the
uptake of vitellogenin (Vtg) and that it is associated with the
low previtellogenic E2 plasma levels, while a significant E2
increase in plasma is associated with the beginning of Vtg
uptake. This would appear to confirm the hypothesis that the
differential and sequential induction of zonagenesis and
vitellogenesis may reflect a general feature of teleost oogenesis.