Yolk protein changes dying oocyte growth in European sea bass Dicentrarchus labrax L.

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Abstract
Oocyte growth within the follicle is due to the accumulation of the normal cytoplasmic components, and the endocytosis of hepatic derived rotein, the vitellogenins. Vitellogenesis started in 200μm oocytes; during oocyte growth the olk Lbules increased in number and size. Yolk globule morphology varies durin oocyte growth: irst Jey appear uniform and dense; then, in 500 μm oocytes they oten appear to be divided into 2 or 3 dense masses. Yolk proteins of pre-maturational oocytes at different stages were compared with those of ovulated eggs by SDS gel electrophoresis. The largest comonents stained by Coomassie blue and those stained by Stains-all, which had formed during viteligenesis, either disappeared or diminished, while smaller components appeared. The changes in yolk rotein banding patterns during oocyte maturation are suggestive of extensive secondary proteol sis of yolk proteins; such secondary proteolysis may generate, as in other marine teleosts, part of the osmotic gradient associated with the resumption of oocyte meiotic maturation, before ovulation.

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