Ovarian dynamics in picarel (Spicara smaris, L., Sparidae) and implications for batch fecundity and spawning interval estimation

Abstract

This study assessed ovarian dynamics in picarel and examined how it can be implemented in routine calculations of batch fecundity and spawning interval. Samples of picarel were collected in Saronikos Gulf, Greece, and ovaries were examined through both histological and whole mount procedures. Three different and independent approaches were applied to assess ovarian modality: (a) the multimodal analysis in oocyte size frequency distributions (OSFD), (b) the histological grouping of oocytes to different cohorts and (c) the ratio of the total number of secondary growth oocytes to the oocytes of the advanced mode. The output from all three methods was in good agreement to each other, suggesting that picarel contains in average 3 to 5 oocyte cohorts throughout the spawning period. Further study of OSFD revealed that the advanced oocyte mode (AM) was clearly distinct since the onset of the spawning season in February and it either partially overlapped with or was separated from smaller oocytes. The gravimetric estimate of relative fecundity of the advanced mode (RFAM) in hydrated females equaled to 336 oocytes g−1 (± standard error16.23) and was comparable to the RFAM from other stages, with and without hiatus in the OSFD. These results show that batch fecundity in picarel can be estimated even in non-hydrated females. Considering the temperature dependent duration of posyovulatory follicle (POF) degeneration, the prevalence of recent spawning markers and their co-occurrence with imminent spawning markers, we conclude that spawning interval in picarel at peak spawning should be between 2 and 4 days.