Oogenesis and spermatogenesis in round sardinella (Sardinella aurita Valenciennes, 1847) from the eastern part of the Adriatic Sea

Background and purpose: Small pelagic fish species round sardinella (Sardinella aurita) has expanded its habitat during the last few decades towards colder parts of the Mediterranean Sea. In the Adriatic Sea, this investigation is the first attempt to study its gonad development histologically.Materials and methods: S. aurita specimens were sampled monthly from commercial landings of purse seine catches from the eastern part of the Adriatic Sea from November 2007 to January 2009. After biometric parameters were determined, gonads were removed from the fish and weighed. Sex and gonad development were determined macroscopically by the shape and the structure of gonads and afterwards gonads were analysed histologically.Results: The phases of gonadal development of both sexes of S. aurita were: immature, developing, spawning capable, regressing, and regenerating. An annual reproduction cycle based on gamete development revealed five stages of oocyte development: chromatin nucleolar stage, perinucleolar stage, yolk vesicle (cortical alveoli) formation, vitellogenic (yolk) stage, and ripe (mature) stage. Spermatogenesis was described through three stages: spermatocytogenesis (formation of primary spermatocytes from spermatogonia), meiosis (formation of secondary spermatocytes and spermatids) and spermiogenesis.Conclusions: Gonadal histology analyses of both sex of S. aurita indicated summer spawning manner of this species, with a peak in June-August period.