Oocyte Cohort Analysis: Criteria for an Evaluation of the Reproductive Cycle inSolen marginatus(Pennánt, 1777), (Bivalvia: Solenacea) in Southern Tunisia

Abstract

The purpose of this study was to develop an oocyte maturation scale and to retrace the development of the oocyte cohorts in razor clam populations of Solen marginatus (Bivalvia: Solenacca Mollusca) sampled in the tidal area of Maltine Wadi (El Mares, Gulf of Gabes, Southern Tunisia). The development of an oocyte maturation scale could help reproductive cycle monitoring and the assessment plan in the search for populations. The results included 7,535 oocyte measurements during a 1-y sampling period from May 2007 to May 2008. Based on the qualitative and quantitative analyses of the oocyte measuring activities, we assume a 4-stage maturation process: I, gametogenesis commencement from November through to March, the oocyte diameters are smaller than 15 µm; II, oocyte growth from April through to May, the oocyte diameters range between 15 µm; and 25 µm; III, oocyte maturation from May through to October, oocyte diameters range between 25 µm and 40 µm; and IV, resorption of the gonads from May through to October, the oocyte aspects are irregular, disrupted, or burst. The development of the indices of the dry condition and the oocyte cohorts shows major reproductive activity of the species from April through to October. Initial maturation commences in May followed by a major gamete emission in June. Maturation recovery occurs in July followed by oocyte growth, which continues, and appears to be more rapid during summer and early autumn. The first gamete emission occurs in May during the first oocyte cohort maturity accession and continues until late October, with an irregular time interval between the emissions.