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The editorial "Special Issue: Molecular Advance on Reproduction and Fertility of Aquatic Animals" explores the complexities of reproduction and fertility in commercial aquatic species, emphasizing the importance of sexual dimorphism and monosexual culture for aquaculture efficiency. The document delves into the molecular mechanisms of sex determination and gonadal development in aquatic animals, highlighting the role of genes, markers, and epigenetic modifications in sex differentiation. Additionally, it discusses the impact of environmental factors, such as food availability, on gonad maturation mechanisms, providing insights into adaptation strategies under starvation conditions. The research presented in this special issue contributes to a deeper understanding of reproduction and fertility in aquatic animals through advanced sequencing technologies and genetic analyses. [Extracted from the article]

Simple Summary: The oriental river prawn, Macrobrachium nipponense, is a widely distributed species in freshwater and low-salinity estuarine regions of China and other Asian countries. This species has become an important commercial commodity in China because of its high nutritional value and palatability. There are significant differences in growth between male and female M. nipponense. The aim of this study was to determine the hepatopancreas transcriptome differences between sex-related size differences in M. nipponense. We identified four genes associated with sex-related size differences, as well as six closely related metabolic pathways. The results indicated the molecular mechanism underlying the sex-related size differences and identified key genes and metabolic pathways. This data will be invaluable to support explanations of individual differences between male and female prawns. Macrobrachium nipponense, a commercially popular crustacean species within the Chinese context, is recognized for its exceptional nutritional composition and palatability. There are significant differences in growth between male and female M. nipponense. Herein, transcriptomics was used to determine the hepatopancreas transcriptome differences between sex-related size differences in M. nipponense. We identified 974 differentially expressed genes (DEGs) between the SHE (female) and BHE (male) groups, which were validated using RT-qPCR. The genes encoding matrix metalloproteinase-9 (MM9), Ribosome-binding protein 1 (RBP1), Aly/REF export factor 2, and hematological and neurological expressed 1 (HN1) may play a role in modulating the sex-related size differences observed in M. nipponense. Clusters of orthologous groups and gene ontology functional analysis demonstrated that the DEGs for sex-related size in M.nipponense were associated with various biological functions. The Kyoto Encyclopedia of Genes and Genomes pathways analysis demonstrated that upregulated DEGs were mainly enriched in lysine biosynthesis, tryptophan metabolism, and lysine degradation pathways, whereas the downregulated DEGs were mainly enriched in ascorbate and aldarate metabolism, retinol metabolism, and drug metabolism-cytochrome P450 pathways. The results indicated the molecular mechanism underlying the sex-related size differences and identified key genes. This data will be invaluable to support explanations of individual differences between male and female prawns. [ABSTRACT FROM AUTHOR]

Methyl farnesoate epoxidase (MFE) is a gene encoding an enzyme related to the last step of juvenile hormone biosynthesis. Mn-MFE cDNA has a total length of 1695 bp and an open reading frame (ORF) length of 1482 bp, encoding 493 amino acids. Sequence analysis showed that its amino acid sequence has a PPGP hinge, an FGCG structural domain, and other structural domains specific to the P450 family of enzymes. Mn-MFE was most highly expressed in the hepatopancreas, followed by the ovary and gill, weakly expressed in heart and muscle tissue, and barely expressed in the eyestalk and cranial ganglion. Mn-MFE expression remained stable during the larval period, during which it mainly played a critical role in gonadal differentiation. Expression in the ovary was positively correlated and expression in the hepatopancreas was negatively correlated with ovarian development. In situ hybridization (ISH) showed that the signal was expressed in the oocyte, nucleus, cell membrane and follicular cells, and the intensity of expression was strongest at stage O-IV. The knockdown of Mn-MFE resulted in a significantly lower gonadosomatic index and percentage of ovaries past stage O-III compared to the control group. However, no differences were found in the cumulative frequency of molting between the experimental and control groups. Moreover, the analysis of ovarian tissue sections at the end of the experiment showed differences between groups in development speed but not in subcellular structure. These results demonstrate that Mn-MFE promotes the ovarian development of Macrobrachium nipponense adults but has no effect on molting. [ABSTRACT FROM AUTHOR]

NPC intracellular cholesterol transporter 1 (NPC1) plays an important role in sterol metabolism and transport processes and has been studied in many vertebrates and some insects, but rarely in crustaceans. In this study, we characterized NPC1 from Macrobrachium nipponense (Mn-NPC1) and evaluated its functions. Its total cDNA length was 4283 bp, encoding for 1344 amino acids. It contained three conserved domains typical of the NPC family (NPC1_N, SSD, and PTC). In contrast to its role in insects, Mn-NPC1 was mainly expressed in the adult female hepatopancreas, with moderate expression in the ovary and heart. No expression was found in the embryo (stages CS–ZS) and only weak expression in the larval stages from hatching to the post-larval stage (L1–PL15). Mn-NPC1 expression was positively correlated with ovarian maturation. In situ hybridization showed that it was mainly located in the cytoplasmic membrane and nucleus of oocytes. A 25-day RNA interference experiment was employed to illustrate the Mn-NPC1 function in ovary maturation. Experimental knockdown of Mn-NPC1 using dsRNA resulted in a marked reduction in the gonadosomatic index and ecdysone content of M. nipponense females. The experimental group showed a significant delay in ovarian maturation and a reduction in the frequency of molting. These results expand our understanding of NPC1 in crustaceans and of the regulatory mechanism of ovarian maturation in M. nipponense. [ABSTRACT FROM AUTHOR]

This article presents a study of D-loop sequences to characterize the genetic diversity of wild Macrobrachium nipponense populations in Yixing natural waters including two reservoirs (Hengshan reservoir, HS; Youche reservoir, YC), 3 brooks (Linjin Dang, LJD; Magong Dushan Dang, MDD; Yangshan Dang, YSD) and 3 shallow lakes (Dongjiu lake, DJ; Xijiu lake, XJ; Tuanjiu lake, XJ), and compared the genetic differentiation and population structure with wild populations of Taihu Lake (TH), Yangtze River (YZ), and the main local artificially bred varieties “Taihu No. 2” (TH-2). A 747 bp D-loop sequence fragment was amplified in 321 individuals and the results exhibited a higher content of A+T (80.03%) than C+G (19.97%). A total of 110 haplotypes were identified. The h and π value proved the diversity of these populations was at the same level with high genetic diversity. TH-2 and YZ showed remarkable diversity, and XJ is even better. Fst estimates suggested that YZ and TH-2 were significant differentiation with other Yixing populations (P < 0.05). Three populations from shallow lake (DJ, XJ and TJ) displayed significant differentiated with the left Yixing ones (P < 0.05). The pairwise genetic distance, as well as haplotype network results, also suggested that all these 11 populations did not diverge at the species level ( 0.1) and the nucleotide mismatch distribution analysis showed multiple peaks, giving a conclusion that the populations did not exhibited expansion. All these results suggested that TH-2 and YZ have remarkable diversity, and the germplasm resources and genetic diversity of M. nipponense in Yixing are very good and are suitable for original materials of breeding.