摘要: Stocking density and feed protein sources are critical in aquaculture. This study investigated their effects on growth, stress response, and protein utilization in gibel carp. Fishmeal served as the control diet (diet 1), while it was replaced by a blend of Tenebrio molitor meal, Chlorella meal, Clostridium autoethanogenum protein, and cottonseed protein concentrate in various ratios: 1:1:8:2 (diet 2), 1:1:6:4 (diet 3), and 1:1:4:6 (diet 4). Fish were raised at either a low stocking density (100 fish/cage, 20 fish/m³) or a high density (400 fish/cage, 80 fish/m³), with 6000 fish in total. The interaction of stocking density and diet affected growth and protein utilization. At a stocking density of 20 fish/m³, diet 2 effectively replaced fishmeal without compromising growth performance. At 80 fish/m³, only diet 3 achieved full fishmeal replacement without negative impacts on growth. High stocking density induced chronic stress, as seen by lower plasma glucose and higher muscle heat shock protein 70 and lactate levels. It also impaired intestinal function and muscle growth at the transcript level, reducing villus height and resulting in poorer growth performance. Diet 4 decreased trypsin and chymotrypsin activities, lowered villus height and the villus height/crypt depth ratio, and reduced plasma and muscle amino acid levels. It also downregulated genes involved in muscle protein synthesis, leading to reduced protein utilization. In conclusion, the optimal protein blend ratio was 1:1:8:2 ​at lower stocking densities and 1:1:6:4 ​at higher stocking densities, both of which achieved growth performance comparable to fishmeal. This density-specific protein blending strategy offers a scalable approach to formulating fishmeal-free feeds for intensive aquaculture systems without compromising productivity.

摘要: The process of gonadal development necessitates the self-renewal and differentiation of germ cells, which is a complex and precisely regulated procedure that is inextricably linked with the gonadal microenvironment. However, our understanding of the microenvironment of the gonads remains incomplete in invertebrates. In the present study, we employed single-cell transcriptome sequencing to examine the early differentiated gonad of a simultaneous hermaphroditic scallop, Argopecten irradians. A total of six clusters were identified, comprising 5669 high-quality cells. The clusters were classified into one germ cell cluster and five somatic cell clusters (accessory cell, hemocyte, ciliated cell, fibroblast, and an uncharacterized cluster) based on functional enrichment analysis and the identification of classical marker genes. The cell types were validated through in situ hybridization. In addition, a weighted gene co-expression network analysis (WGCNA) was employed to elucidate the co-expression patterns of these clusters, which identified key transcription factors in these modules (e.g., Hr38, Mycbp, and Nkx2.5) and revealed that germ cells exhibited a high degree of connectivity with accessory cells. Further analysis demonstrated the existence of two subsets of germ cells with a continuous developmental trajectory and three subclusters of accessory cells, including an ovary-unique cell type. A substantial number of bidirectional ligand–receptor interactions were observed between germ cells and accessory cells, including those involving the TGF-β, Notch, PI3K-Akt, and Wnt signaling pathways. Our study elucidates the cellular composition and gonadal microenvironment of A. irradians at the single-cell level, thereby providing new insights into a comprehensive understanding of the development of germ cells in bivalve mollusks.

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摘要: Silver carp (Hypophthalmichthys molitrix) is one of the four major Chinese carps and is widely distributed throughout the country. Notably, silver carp feeds on plankton and plays an important role in controlling blue-green algal blooms and purifying water quality in fisheries. However, this species is less tolerant to low oxygen and tends to die under high-density aquaculture conditions and during long-distance transport, leading to huge economic losses. In this study, we employed metabolomic analyses to liver tissue of silver carp subjected to varying degrees of hypoxic stress, resulting in the identification of 593 metabolites in total and 268 differential abundance metabolites (DAMs). As hypoxia stress intensifies, 30 distinct DAMs were consistently identified in silver carp across hypoxia, semi-asphyxic, and asphyxic states. Receiver operating characteristic analysis of these metabolites suggests their potential utility as biomarkers for hypoxia stress. The KEGG pathway enrichment analysis of DAMs revealed significant enrichment in pathways related to amino acid metabolism and synthesis, as well as glucose metabolism. Comprehensive metabolic flow charts were developed to systematically illustrate the hypoxia-induced alterations in metabolites associated with pathways such as amino acid biosynthesis, arginine biosynthesis, glycolysis/gluconeogenesis, alanine, aspartate, and glutamate metabolism, in addition to galactose metabolism. In addition to these findings, the ferroptosis signaling pathway was enriched as a result of hypoxia. Ferroptosis is a novel form of cell death that is dependent on iron. To ascertain the occurrence of ferroptosis, sensitive indicators associated with ferroptosis were examined, and the results substantiated the presence of ferroptosis in the liver of silver carp under hypoxia conditions. Subsequently, CRISPR/Cas9 technology was performed on silver carp to knock out the acsl4 gene that promotes lipid peroxidation in the ferroptosis pathway, and P0 generation chimeric silver carp was obtained. Experiments on wild-type silver carp and P0 generation chimera revealed that acsl4-deficient chimera had greater hypoxia tolerance. Indicators linked to ferroptosis showed that disrupting acsl4 could reduce hypoxia-induced ferroptosis. Findings could provide valuable insights into the molecular mechanisms underlying hypoxia-induced adaptation and injury in the liver of fish, and could provide a valuable reference for the cultivation of fish species that exhibit tolerance to hypoxic conditions.

摘要: To understand the progression of metaflammation, elucidating the age-dependent role of SOCS8 deficiency in socs8^−/− zebrafish is crucial, as this may serve as a disease model for metabolic disorders because of the gradual dysregulation of immunity, metabolism, and the gut microbiota observed in this species. Thus, both juvenile (1-month-old) and adult (3-month-old) mutant socs8^−/− as well as wild-type zebrafish were tested for changes in growth, histopathology, transcriptomes, and microbiota composition. Histological analysis revealed a marked increase in oil droplets and a reduction in hepatocyte nuclear density for the comparison between socs8^−/− and wild type fish, indicative of metabolic dysfunction-associated fatty liver disease (MAFLD). The liver in 1-month-old (1 ​mo) socs8^−/− zebrafish had changes in “arginine and proline metabolism”, alongside an increased percentage of M0 and M2 macrophages. This suggests a protective response from macrophages, which is consistent with the GO term of “negative regulation of leukocyte differentiation”. The enhanced fatty acid metabolism in 1 ​mo may serve as an indicator of free fatty acid-induced hepatotoxicity associated with simple steatosis but not with liver dysfunction. These findings aligned with the higher growth of 1 ​mo socs8^−/− fish. In 3-month-old (3 ​mo) socs8^−/− fish, the GO terms “steroid hormone biosynthesis” and “steroid metabolic process” indicated the presence of endoplasmic reticulum stress, which contributes to the development of steatohepatitis. DNA repair pathways and associated terms indicated hepatocyte death. The presence of increased dendritic cells, along with expanded activated dendritic cells in nonalcoholic steatohepatitis (NASH), indicated that the 3 ​mo socs8^−/− model may represent the late stage of MAFLD. In the gut, imaging results from larvae and single-cell sequencing of intestinal mucosa cells from 3 ​mo socs8^−/− fish revealed a consistent accumulation of lymphocytes, with the number of innate immune cells higher in larvae but lower in adult fish, compared to wide type fish. In the 1 ​mo socs8^−/− fish, enhanced mucin secretion, suggested by a greater number of goblet cells and upregulated “SNARE interactions in vesicular transport”, was in line with “mannose type O-glycan biosynthesis”. The same group had upregulated IL-13 and its receptors, aligning with the GO term “wound healing” and the idea that innate lymphocytes producing IL-13 may function as regulators of immunity and tissue remodeling. The enriched pathways “arachidonic acid metabolism” and “intestinal immune network for IgA production” at 1 month, indicating enhanced proliferation of intestinal epithelial cells and improved host‒microbe interactions, respectively. Comparing 1 ​mo socs8^−/− with wide type fish, higher levels of Prevotella indicate enhanced glucose metabolism due to their role in polysaccharide breakdown. Meanwhile, lower levels of Veillonella indicate oxidative stress, potentially associated with a reduced lumen at one month. Intestinal bacterial overgrowth in 3 ​mo socs8^−/− fish (compared to 1 ​mo socs8^−/−) contributes to the exacerbation of liver dysfunction. Compared 3 ​mo socs8^−/− with wide type fish, despite an increase in T/NK cells, elevated fatty acid metabolism may impair the function of intestinal lymphocytes. Therefore, the symptoms observed in the gut‒liver axis suggest that socs8^−/− zebrafish may serve as a model for MAFLD.

摘要: The insulin-like androgenic gland hormone (IAG) plays a crucial role in male sexual differentiation. Although the putative IAG receptor has been identified in several crustacean species, IAG receptor in brachyuran crabs has yet to be determined. This study identified a new insulin-like receptor (Sp-IR2) in the mud crab Scylla paramamosain, and explored its possible role in spermatogenesis. RT-PCR results suggested that Sp-IR2 was highly expressed in the androgenic gland (AG) and testes. During testicular development, the levels of Sp-IR2 transcript in the AG and testes gradually increased. In addition, bovine insulin significantly up-regulated the expression of Sp-IR2, Sp-vasa and Sp-sox9 in the testes in vitro. Injection of bovine insulin induced Sp-vasa and Sp-dsx expression in the testes, and increased hemolymph testosterone titer. In vitro silencing of Sp-IR2 significantly increased the expression levels of Sp-IR1 and Sp-vasa transcripts in the testes. To further investigate the function of Sp-IR2 in testicular development, we performed short- and long-term RNA interference (RNAi) on male crabs. Short-term knockdown of Sp-IR2 led to the significant up-regulation of Sp-IR1 in the testes and AG, and Sp-vasa in AG. Prolonged silence of Sp-IR2 markedly reduced the expression of Sp-sox9 in testes, and arrested spermatogenesis at the secondary spermatocyte stage, suggesting Sp-IR2 plays an important role in transitioning secondary spermatocytes to spermatids. In combination with our previous study, our results indicated that insulin-like receptor signaling pathways are important for spermatogenesis in S. paramamosain, in which Sp-IR1 is involved in transitioning of primary spermatocytes to secondary spermatocytes while Sp-IR2 is essential for the transition of secondary spermatocytes to spermatids.

摘要: The diversity of marine habitats influences fish trophic niches and adaptation strategies. This study investigated fish trophic niches in cold seep and adjacent areas of the South China Sea in August 2023 using stable isotope techniques. It examined these niches across different depths and compared trophic strategies between cold seep and non-cold seep habitats. The δ¹⁵N values of fish in the cold seep area increased with depth, indicating shifts in trophic levels, while the δ¹³C values increased solely in the cold seep area. Bayesian analysis revealed that deeper fish in the cold seep area preferred shrimp, whereas those in the control area leaned towards cephalopods. At depths exceeding 500 ​m, the trophic niche of the fish community in the cold seep area was broader than that in the control area, although the individual niches of shared species were narrower. This finding suggests a balance between resource diversity and individual feeding specialization within the cold seep fish community at greater depths. In contrast, individual niches in the control area expanded to adapt to a resource-limited environment. Additionally, the overlap of trophic niches between deep-sea and shallow-water fish diminishes with increasing depth in both regions. We hypothesize that beyond a certain depth, mesopelagic fish either cease vertical migration or modify their patterns of vertical migration. These results underscore the essential role of cold seep ecosystems in sustaining deep-sea biodiversity and intricate trophic structures, thereby enhancing our understanding of adaptive strategies in deep-sea fish communities.

摘要: The Anthropocene era is characterized by the far-reaching impacts of human activities on the biosphere, making it a critical time for ecological conservation and management. One of the most direct and ongoing anthropogenic threats to marine mammals, particularly small cetaceans, stems from fisheries. This study provides the initial evidence of odontocetes interacting with the light falling-net fishery in the South China Sea based on onboard observations from 2020 to 2022. These observations were collected during four voyages from April to June, covering 107 fishing sites and documenting interactions with four odontocete species. The most frequently sighted species was the pantropical spotted dolphin (Stenella attenuata), followed by the spinner dolphin (S. longirostris), Risso’s dolphin (Grampus griseus), and rough-toothed dolphin (Steno bredanensis). We found a higher abundance of fisheries–dolphin interactions in the southern South China Sea compared to the northern region. Commercial fishing patterns showed a high rate of dolphin interactions, suggesting resource competition. Two species of sea turtles were observed interacting with fishing vessels: hawksbill turtles (Eretmochelys imbricataolive) in Nansha and olive ridley turtles (Lepidochelys olivacea) in Dongsha. The findings of this study shed light on the potential impact of commercial fishing activities on dolphin populations and behaviors, underscoring the urgent need for stakeholders to develop sustainable fishing practices that mitigate detrimental consequences on cetaceans and preserve the health of marine ecosystems.

摘要: Pyropia yezoensis, a vital intertidal seaweed, plays a crucial role in the preservation of marine biodiversity. In recent years, the rapid expansion of its cultivation has raised concerns regarding the sustainability of seaweed aquaculture practices. However, research on gene exchange among P. yezoensis populations remains limited. In this study, we conducted a comprehensive analysis of gene flow using 228 whole-genome resequencing samples from key wild and cultivated P. yezoensis populations in China, as well as populations from Japan. We identified seven potential gene flow events, with gene flow regions encompassing 0.3%–25.43% of the genome. Genetic analysis revealed that these genomic regions were characterized by high genetic diversity, low genetic differentiation, and increased coding DNA sequence (CDS) density and guanine-cytosine (GC) content. Moreover, 53% of these regions contain at least one signal of selection, with genes involved in RNA and protein processing, transport, cellular homeostasis, and stress response functions associated with thallus growth, development, and stress resistance suggesting a role in environmental adaptability and artificial selection. Notably, we found that the genetic load in cultivated populations was significantly higher than in wild populations; fortunately, gene flow was not the primary factor driving this phenomenon. On the contrary, we found that gene flow events in two trios significantly reduced the genetic load caused by loss-of-function mutations. These findings enhance our understanding of intraspecific gene flow in seaweeds and provide valuable insights for the sustainable cultivation of seaweed aquaculture.