Abstract
The Mediterranean swordfish (Xiphias gladius) has been recently classified as overfished and in 2016, the International Commission for the Conservation of the Atlantic Tunas (ICCAT) established a multi-annual management plan to recover this stock. To successfully achieve this goal, knowledge about swordfish biology is needed. To date, few studies on swordfish have been performed and none of them has provided useful insights into the reproductive biology at molecular level. Here we set to characterise the molecular dynamics underlying ovarian maturation by employing a de novo transcriptome assembly approach. Differential gene expression analysis in mature and immature ovaries identified a number of differentially expressed genes associated with biological processes driving ovarian maturation. Focusing on ovarian steroidogenesis and vitellogenin uptake, we depict the molecular dynamics characterizing these processes while a phylogenetic analysis let us identify a candidate vitellogenin receptor. This is the first swordfish transcriptome assembly and these findings provide in-depth understanding of molecular processes describing ovarian maturation. Moreover, the establishment of a publicly available database containing information on the swordfish transcriptome aims to boost research on this species with the long-term of developing more comprehensive and successful stock management plans.
Highlights
The swordfish (Xiphias gladius Linnaeus, 1758) is a large, solitary, fast-swimming and highly migratory species with a worldwide distribution
Since the overarching goal of our study was to investigate the molecular dynamics underlying ovarian maturation, we focused our effort in the identification of differentially expressed genes between mature and immature ovaries and livers
We focused on data obtained from mature and immature ovaries in order to improve our understanding of specific molecular pathways driving sexual maturation in this species and to enhance both conservation and management of this resource for the Mediterranean fisheries
Summary
The swordfish (Xiphias gladius Linnaeus, 1758) is a large, solitary, fast-swimming and highly migratory species with a worldwide distribution. Since that time, robust management plans have been lacking due to the scarcity of information on reproduction, growth, sexual maturity and migratory behaviour Such a lack of knowledge is caused by clear logistic constraints associated with collecting samples in pelagic areas which often require collaboration with fishermen and ad-hoc sampling surveys. Gonadotropin releasing hormone (GnRH) from the hypothalamus stimulates the synthesis and release of the gonadotropins follicle stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary, which in turn act on the gonads inducing oogenesis and spermatogenesis mainly through the stimulation of gonadal steroidogenesis This cascade has been well characterized in many fish species[11,12], the mechanisms underlying the onset of puberty are not fully understood. This work represents the first swordfish de novo transcriptome assembly and such findings provide the additional knowledge needed to refine current ICCAT recovery plan towards a successful conservation of the Mediterranean swordfish
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