ASSESSMENT OF REPRODUCTIVE CYCLE IN COMMON SOLE BY CITOMETRY

The common sole Solea solea (L., 1758) is one of the most valuable resources and it is a target fishery species in Mediterranean water, but guidelines about the resource management are generally lacking. In order to increase the scarce knowledge on the annual maturative cycle of the ovary, in the Adriatic Sea, histological and cytological analyses of ovary obtained from monthly captures of sole were carried out. Cytometric analysis was carried out by a computerized image analysis system Leica Qween. The gonad-somatic index (GSI determined on the basis of the ovary to body weight ratio), supported by histological and cytological data, describe the spawning period from December to March. The GSI increased rapidly during the reproductive season, when the majority of oocyte growth (diameter > 200 mm) occurred. The range of germinal cells is comprised between 8 mm (oogonia) and 1.360 mm (hydrated oocytes immediately before spawning). The cytological study of oocyte size distribution showed only previtellogenic oocytes (diameter < 200 mm), during the period April-November, but also vitellogenic oocytes (diameter > 200 mm), during the period December-March. Before ten years ago, the oocyte size distribution in the mature ovaries was rarely studied in populations of common sole and the data obtained were often conflicting. In conclusion, the cytological approach applied throughout the ovary maturation cycle in common sole is a good “assessment environmental test” as gonad maturation is closely dependent on environmental conditions.