Pattern of oocyte development and batch fecundity in the Mediterranean sardine
In the present study, the pattern of oocyte development was investigated in the Mediterranean sardine (Sardina pilchardus sardina) in order to examine whether non-hydrated females could be included in batch fecundity measurements. Gonad histology and frequency distributions of oocyte diameters demonstrated that the Mediterranean sardine exhibits group-synchronous type of oocyte development. The spawning batch begins to separate in size from the adjacent population of smaller oocytes at the secondary yolk globule stage and a well-developed size-hiatus is established at the tertiary yolk globule stage. The spawning batch could be clearly identified prior to hydration and batch fecundity-on-fish weight relationships did not differ significantly between hydrated females and females at the tertiary and migratory nucleus stages. Thus, apart from hydrated females, batch fecundity in the Mediterranean sardine may also be measured by the use of females at the tertiary and migratory nucleus stages. Relative fecundity was shown to be independent of body weight and its estimates during the respective peak spawning months for the Aegean Sea and Ionian Sea stocks were 360 eggs/g (December 2000) and 339 eggs/g (February 2001). (C) 2003 Elsevier B.V. All rights reserved.