Abstract
During folliculogenesis, primary oocytes of teleosts grow by several orders of magnitude by-self synthesizing proteins and mRNA, or sequestering from blood specific macromolecular components, such as fatty acids and vitellogenin. All these materials are stored into cortical alveoli, yolk globules or oil droplets during oocyte development. The proper synthesis, storage and displacement of these macromolecular components inside the oocyte play a key role for a successful fertilization process and for the subsequently correct embryo development. In this study, for the first time, the FTIR Imaging (FTIRI) spectroscopy has been applied to characterize the chemical building blocks of several cellular components of swordfish oocytes at different developmental stages. In particular, the spectral features of previtellogenic (PV), vitellogenic (VTG), mature (M) and atretic (A) follicles as well as and of cortical alveoli (CA), yolk vesicles (YV), oil droplets (OD) and Zona Radiata (ZR) have been outlined, providing new insights in terms of composition and topographical distribution of macromolecules of biological interest such as lipids, proteins, carbohydrates and phosphates. The macromolecular characterization of swordfish oocytes at different developmental stages represents a starting point and a useful tool for the assessment of swordfish egg quality caught in different conditions, such as periods of the year or different fishing area.
Highlights
Mediterranean Swordfish (Xiphias gladius) is a large, highly migratory and valuable commercial species, which has been recently put through a stock recovery plan by the International Commission for the Conservation of Atlantic Tunas (ICCAT)
Its oogenesis is similar to those described for other oviparous species with asynchronous development
By analyzing the morphological features of ovaries, it is possible to detect at the same time the occurrence of follicles at different maturation stages
Summary
Mediterranean Swordfish (Xiphias gladius) is a large, highly migratory and valuable commercial species, which has been recently put through a stock recovery plan by the International Commission for the Conservation of Atlantic Tunas (ICCAT). Until now, information on its reproduction is scarce[4,5], even if a deep knowledge on its reproductive potential is mandatory for studies on stock assessment and management In this light, the objective of the present study was to characterize the biochemical composition and structure of swordfish oocytes at different developmental stages. Several reports exploited FTIRI to characterize the biochemical changes associated with oocyte growth and maturation, in various species including fish[9,10,11,12,13] Recently, this spectroscopic tool has been applied to evaluate the macromolecular alterations induced in zebrafish by feed additives and pollutants[14,15,16]. By understanding the molecular and morphological changes that occur in oocytes, it will be possible to identify critical checkpoints in the reproduction of this endangered species
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