The greater amberjack (Seriola dumerili) is an emerging marine fish that is increasingly favored in aquaculture. Currently, there are few studies on the development and regulation of greater amberjack ovaries. In this study, the ovary transcriptome profiles of greater amberjack at three different stages (stage II, III, and IV) were performed, and identified the genes and pathways that may play significant roles in the processes of follicle growth and maturation. A total of 6597, and 1061 differentially expressed genes (DEGs) were detected in FII vs. FIII, FIII vs. FIV, and FII vs. FIV stages, respectively. GO and KEGG enrichment analyses revealed that these DEG_S are primarily involved in steroid hormone biosynthesis (e.g., cyp11a1, cyp17a1, cyp19a1a, hsd3b1, esr1), lipid metabolism (e.g., plpp3, lpl, pld1, and fabp10a), and meiotic arrest and resumption (e.g., pgr, arb, ccnd2, adcy2, adcy9, myl9, calm1). Additionally, several signaling pathways involved in ovarian development have been identified, including the PI3K-Akt, Wnt, TGF-beta, GnRH, and immune-related signaling pathways. qPCR results of nine representative genes related to steroid hormone synthesis and cell growth verified the reliability of the generated RNA-seq data. This research contributes to our comprehension of the molecular processes underlying ovarian growth and maturation in marine fishes and provides a theoretical basis for the investigation of functional genes associated with oogenesis in greater amberjack.

The greater amberjack (Seriola dumerili) is a gonochoristic fish with no sexual dimorphism in appearance, making sex identification difficult. Piwi-interacting RNAs (piRNAs) function in transposon silencing and gametogenesis and are involved in various physiological processes, including sex development and differentiation. Exosomal piRNAs can be indicators for the determination of sex and physiological status. In this study, four piRNAs were differentially expressed in both serum exosomes and gonads between male and female greater amberjack. Three piRNAs (piR-dre-32793, piR-dre-5797, and piR-dre-73318) were significantly up-regulated and piR-dre-332 was significantly down-regulated in serum exosomes and gonads of male fish, compared to female fish, consistent with the serum exosomal results. According to the relative expression of four marker piRNAs derived from the serum exosomes of greater amberjack, the highest relative expression of piR-dre-32793, piR-dre-5797, and piR-dre-73318 in seven female fish and that of piR-dre-332 in seven male fish can be used as the standard for sex determination. The method of sex identification can ascertain the sex of greater amberjack by blood collection from the living body, without sacrificing fish. The four piRNAs did not show sex-inclined expression in the hypothalamus, pituitary, heart, liver, intestine, and muscle tissue. A piRNA–target interaction network involving 32 piRNA-mRNA pairs was generated. Sex-related target genes were enriched in sex-related pathways, including oocyte meiosis, transforming growth factor-beta signaling pathway, progesterone-mediated oocyte maturation, and gonadotropin releasing hormone signaling pathway. These results provide a basis for sex determination in greater amberjack and improve our understanding of the mechanisms underlying sex development and differentiation in the species.

Marine heatwaves (MHWs) have recently become more frequent, intense, and prolonged, posing significant threats to marine life and fisheries. In this study, transcriptomic analysis was employed to investigate the genes and pathways in Seriola dumerili that respond to MHW-induced stress at 28 °C (T28) and 32 °C (T32), using 24 °C (T24) as the control. Transcriptome sequencing revealed that 17 differentially expressed genes (DEGs) belonging to the heat shock protein (HSP) families—HSP30, HSP40, HSP70, and HSP90—were significantly upregulated under short-lasting MHW stress in the T24-4d vs. T32-4d comparison. Additionally, genes related to oxidative stress (e.g., protein disulfide isomerase family A member 6 [pdia6]), immune responses (e.g., interferon regulatory factor 5 [irf5]), and energy metabolism (e.g., hexokinase-1 [hk1]) were also identified. Enrichment analysis of DEGs in the T24-4d vs. T32-4d group revealed that S. dumerili exhibited adaptive responses to MHWs through the upregulation of HSPs and the activation of antioxidant, energy metabolism, and immune response pathways. However, in the T24-13d vs. T32-13d group, DEGs associated with these pathways were either not significantly expressed or were downregulated. These findings indicate that S. dumerili is unable to sustain its adaptive responses under repeated, intense MHW exposure, resulting in the disorder of its antioxidant defense system, immune suppression, and metabolic dysfunction. This study provides valuable insights into the molecular responses of S. dumerili to MHWs and supports the selection for thermal resistance in this species.

The greater amberjack (Seriola dumerili) is a globally important aquaculture fish species belonging to the family Carangidae. However, current research on the ovarian development and regulation of the greater amberjack is limited, particularly with regard to early ovarian development in artificially bred individuals. Therefore, this study aims to analyze the ovarian transcriptomes at the primary growth stage in one-year-old fish at the chromatin nucleolar stage and two-year-old fish at the perinucleolar stage to suggest how early ovarian development takes place in artificially bred greater amberjacks. To do this, the study constructed ovarian mRNA expression profiles of different stages of artificially bred fish and identified differentially expressed genes (DEGs), Gene Ontology terms, and Kyoto Encyclopedia of Genes and Genomes pathways important for various physiological processes. A functional analysis revealed that the DEGs closely related to ovarian development were involved in cell growth and death (e.g., ccnd1, cdk1, cdc6, cdc25b, fbxo43, cdkn1a and cdkn1d), the TGF-beta signaling pathway (e.g., gdf6, bmpr1b, gsdf, amh, tgfb3, and smad6), steroid hormone biosynthesis (e.g., hsd3b1, hsd11b2, hsd17b12 and hsd20b2), and the endocrine system (e.g., mapk8a, mapk11, mapk12a, mapk13 and adcy9). These findings suggest that ovarian development is the result of the coordinated regulation of various genes responsible for various functions. This study provides a theoretical basis for exploring the underlying molecular mechanisms of early ovarian development in artificially bred greater amberjacks.

In order to explore the main regulatory genes and related pathways of growth traits, transcriptome sequencing was performed on the hypothalamus, pituitary, and liver tissues of 12-month-old greater amberjack (Seriola dumerili) with different growth rates. In total, 504 (118 up- and 386 down-regulated), 556 (283 up- and 273 down-regulated), and 699 (224 up- and 475 down-regulated) differentially expressed genes (DEGs) were identified in the hypothalamus, pituitary, and liver tissues, respectively. GO and KEGG pathway analyses revealed significant differences in the expression of several genes involved in growth, metabolism, and immune-related pathways. The mRNA expression levels of genes related to growth (ghrh, ghra, igf1), cell proliferation (fgf19, fgfr4, mapk8b, map2k4b, and map4k3), and lipid metabolism (acsl5, dgat2, lipeb, cyp7a1, and fabp10a) were up-regulated in the fast-growing (FG) group, while the cartl and sst1.1 were down-regulated. Conversely, genes associated with glycolysis (fbp1a, pklr, pgm2), citrate cycle (aclya, idh1), and immune-related pathways (irf1b, cxcl10, tnfb, lysg, ifi44, mapk11, and mapk12b) were up-regulated in the slow-growing (SG) group. These findings indicate that the FG exhibited greater lipid metabolism capacity and cell proliferation ability, while the SG expended additional energy to cope with environmental stress, with hindered growth during immune response. This study enhances our understanding of the genetic mechanisms underlying differences in growth rates and provides essential gene resources for future growth-related molecular breeding programs in greater amberjack.