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Larimichthys crocea (also known as the large yellow croaker) is one of the most economically important marine fishes in China, and research on the ecology and genetics of this species is of immense significance. In this study, we performed restriction site-associated DNA sequencing (RAD-seq) of 54 individuals collected from four sites in China to analyze the genetic structure and diversity of large yellow croaker at the genome level. It revealed that the large yellow croaker populations in the Ningde and Zhoushan coastal waters can be clearly distinguished. Different genetic diversity indices were used to analyze the genetic diversity of the large yellow croaker, which showed that there was a differentiation trend between the wild and farmed populations in Ningde. Moreover, we identified genetically differentiated genomic regions between the populations. GO gene enrichment analysis identified genes that are related to fatty acid metabolism and growth. These findings enhance our understanding of genetic differentiation and adaptation to different living environments, providing a theoretical basis for the preservation and restoration of the genetic resources of the large yellow croaker. [ABSTRACT FROM AUTHOR]

Chemical cues and pheromones mediate fish reproduction, aggregation, risk assessment, and kin recognition. To better understand the chemical communication of conspecific fish, the behavioral responses to bile acids (BAs), their source, and reception investigated in large yellow croaker (Larimichthys crocea). Behavioral experimental results indicated that juvenile fish were attracted to intestinal contents (ICs) emanating from conspecifics, regardless of whether the fish were feeding. IC BA-targeted metabolomics revealed that cholic acid (CA), taurocholic acid (TCA), taurochenodeoxycholic acid (TCDCA), chenodeoxycholic acid (CDCA), and taurodeoxycholic acid (TDCA) were the top five categories. Tests with and without fasting yielded similar categories and proportions of BAs, indicating that the intestinal BA profiles were generally stable. At the nanomolar level, CA led to significant preference behavior (p < 0.01). The electrophysiological results supported the hypothesis that the top five BAs were potent odorants in L. crocea. Moreover, inhibition of adenylate cyclase–cyclic adenosine monophosphate (AC–cAMP) signaling and phospholipase C (PLC) signaling reduced the electro-olfactogram (EOG) responses to CA and CDCA. Collectively, the findings of this study indicate that conspecific individuals could be attracted by ICs unrelated to feeding. As a key intestinal BA, CA led to fish preference behaviors and olfactory responses relying on cAMP and PLC transduction cascades. [ABSTRACT FROM AUTHOR]

Large yellow croaker is an economically important fish in China and East Asia. Despite its economic importance, genome-wide adaptions of domesticated large yellow croaker are largely unknown. Here, we performed whole-genome resequencing of 198 individuals of large yellow croaker obtained in the sea or from farmers in Zhoushan or Ningde. Population genomics analyses revealed the genetic population structure of our samples, reflecting the living environment. Each effective population size is estimated to be declining over generations. Moreover, we identified genetically differentiated genomic regions between the sea-captured population in the Zhoushan Sea area and that of the Ningde Sea area or between the sea-captured population and the farmed population in either area. Gene ontology analyses revealed the gene groups under selective sweep for the adaptation to the domesticated environment. All these results suggest that individuals of the large yellow croaker populations show genomic signatures of adaptation to different living environments. [ABSTRACT FROM AUTHOR]

Large yellow croaker iridovirus (LYCIV) poses a growing threat to large yellow croaker (Larimichthys crocea) aquaculture, requiring early diagnosis for effective prevention and control. However, current detection methods are time-consuming, labor-intensive, or require specialized equipment, hindering timely diagnosis. To address this concern, we developed a novel platform combining CRISPR/Cas12a and recombinase polymerase amplification (RPA) for rapid and sensitive LYCIV detection. Our strategy targeted the conserved ATPase gene, utilizing specific crRNA and RPA primers for selective detection. Additionally, we employed a lateral flow strip technique for intuitive visual assessment. The performance evaluation demonstrated outstanding specificity and sensitivity, with a limit of detection as low as 5 × 103 copies / reaction of iridovirus. Validation on spiked and clinical fish samples confirmed the accuracy through PCR analysis. Overall, our developed platform offers a convenient, on-site, and user-friendly tool for early diagnosis, prevention, and control of LYCIV-related diseases in large yellow croaker aquaculture. • A CRISPR/Cas12a-powered platform was developed to detect large yellow croaker iridovirus. • The specific crRNAs and RPA primers were designed to target the ATPase gene. • This platform was a convenient, on-site, and user-friendly iridovirus detection tool. [ABSTRACT FROM AUTHOR]

Pseudomonas plecoglossicida is a Gram-negative bacterium that causes chronic granulomatous diseases in fish. However, the molecular mechanisms underlying its pathogenicity are poorly understood. Here, we identified a novel two-component system (TCS) named PvgAS in P. plecoglossicida , which regulates the expression of genes including the type VI secretion system-1 (T6SS-1), a key virulence factor, as well as the type III secretion system (T3SS) gene cluster and several genes associated with metabolic pathways. We showed that PvgAS is essential for bacterial virulence in large yellow croaker (LYC), an important aquaculture species, by controlling T6SS-1 expression, which is crucial for tissue colonization and intracellular survival. In contrast, T3SS was dispensable for P. plecoglossicida virulence in this model. We also confirmed T6SS-1 gene regulation by PvgAS at the transcriptional and translational levels using RNA-seq, RT-qPCR, lacZ reporter, and western blot assays. Our study reveals a regulatory and functional role of PvgAS in P. plecoglossicida pathogenicity and suggests that PvgAS may be a potential target for new therapeutic interventions against this bacterium. • Identified a novel two-component system PvgAS in Pseudomonas plecoglossicida. • PvgAS regulates type III and type VI secretion systems and bacterial virulence. • T3SS is dispensable but T6SS-1 is essential for P. plecoglossicida pathogenicity. • PvgAS is a potential target for developing new therapeutic interventions. [ABSTRACT FROM AUTHOR]

Dietary fish oil (FO) replacement has led to an inflammatory response in fish species. This study aimed to identify immune-related proteins in the liver tissue of fish fed a FO-based or soybean oil (SO)-based diet. By conducting proteomics and phosphoproteomics analyses, a total of 1601 differentially expressed proteins (DEPs) and 460 differentially abundant phosphorylated proteins (DAPs) were identified, respectively. Enrichment analysis revealed immune-related proteins involved in bacterial infection, pathogen identification, cytokine production, and cell chemotaxis. The mitogen-activated protein kinase (MAPK) pathway exhibited significant alterations in both protein and phosphorylation levels, with several hub DEPs and DAPs associated with MAPK pathway and leukocyte transendothelial migration being notable. In vitro experiments indicated that linolenic acid (LNA), derived from SO, inhibited the expression of NF-E2-related factor 2 (Nrf2), but increased the expression of signaling proteins linked to nuclear factor κB (NF-κB) and MAPK pathways. Transwell assays indicated that treatment of liver cells with LNA promoted macrophage migration. Collectively, the results showed that the SO-based diet upregulated the expression of NF-κB signaling-related proteins and activated the MAPK pathway, promoting immune cell migration. These findings provide novel insights for developing effective solutions to alleviate health problems caused by dietary high levels of SO inclusion. [Display omitted] • The first multi-omics combined analysis of large yellow croakers fed a SO diet. • Dietary SO triggers activation of the NF-κB signaling pathway, leading to inflammation. • SO decreased the antioxidant capacity but increased cytokine gene expression. • SO activated the MAPK pathway, which subsequently facilitated the migration of leukocytes in the fish. • The SO-induced inflammatory response promoted autophagy in the fish. [ABSTRACT FROM AUTHOR]

Pseudomonas plecoglossicida is a facultative Gram-negative bacteria that causes 'visceral granulomas disease' (VGD) in large yellow croaker (LYC; Larimichthys crocea) and several other fish species leading to high economic losses. Currently, there are no commercial vaccines against VGD. Thus, we evaluated the efficacy of a live attenuated vaccine (LAV) made by our laboratory in LYC administered orally in alginate-coated LAV-loaded feeds. To evaluate the tolerance of the LAV in the acidic environment of the stomach, we treated the alginate-coated LAV with a simulated gastric juice without pepsin. There was a 10-fold decrease in the number of viable LAV cells after treatment with the simulated gastric juice (pH 2.0). Despite so, we found a significant increase in LAV cells in the liver and hindgut within 4 h post first feeding of oral vaccine (hpff), which increased to high levels by 24 hpff indicating that LAV cells that survived the stomach acidic environment reached the hindgut for adsorption. Although there was a transient change in the composition of the gut microbiota at 24 hpff, analysis using the Shannon and β-diversity indices showed a similarity in the bacterial composition found before and after vaccination indicating that the LAV had no long-term adverse effect on the gut microbiota. Systemic and mucosal humoral responses were characterized by high serum antibody levels and upregulation of the pig and sign while activation of cell-mediated immunity was characterized by upregulation of MHC-Iα, MHC-IIβ, Prf1 and IFNγ genes. The overall protection in vaccinated LYC was estimated at relative percent survival (RPS) of 60%. Altogether, this study has shown that LAVs can be used as oral vaccines to confer protective immunity without impacting adverse effects on the fish microbiota. • P. plecoglossicida causes 'visceral granulomas disease' (VGD) in large yellow croaker. • This is the first report of a promising live attenuated vaccine against VGD by oral administration. • Oral vaccination confers protective immunity without impacting adverse effects on the fish microbiota. [ABSTRACT FROM AUTHOR]

Apelin, a pleiotropic cytokine with various biological activities, plays important roles in both infectious and noninfectious inflammatory diseases in mammals by regulating immune responses. However, the effect of apelin on the host defenses against microbial infections in teleosts is still unknown. Therefore, this study aimed to characterize the molecular features of apelin in Larimichthys crocea (designated LCapelin) and to investigate the roles of LCapelin in bacterial infection in vivo. The complete open reading frame (ORF) of LCapelin , which encodes a 77-amino acid precursor, was cloned and identified. In healthy fish, LCapelin was constitutively expressed in all 10 tissues examined, and the highest expression level was observed in muscle tissue. Following a challenge with Vibrio parahemolyticus , the mRNA expression of LCapelin was significantly increased at 4 hpi in the spleen. However, in the liver, the expression of LCapelin decreased initially but gradually returned to normal. Furthermore, pretreatment with the synthetic peptide LCapelin-13 prior to Vibrio parahaemolyticus challenge significantly ameliorated clinical signs, inhibited the expression of inflammatory cytokines (TNF-α, IL-1β, and IL-6) in the spleen and liver, decreased the proliferation of splenocytes and melanomacrophage centers (MMCs) in the spleen, and promoted bacterial clearance. Taken together, our results show that LCapelin participates in host defense against V. parahaemolyticus infection in L. crocea and may have potential application in the development of new strategies to combat infectious diseases in teleosts. • LCapelin expression responded to Vibro parahaemolyticus challenge in spleen and liver. • LCapelin significantly ameliorated the clinical signs of experimental vibriosis. • LCapelin inhibited Vibrio parahaemolyticus induced-expression of inflammatory cytokines. • LCapelin promoted bacterial clearance in vivo. [ABSTRACT FROM AUTHOR]

Pseudomonas plecoglossicida is a Gram-negative fish pathogen that affects the large yellow croaker (LYC; Larimichthys crocea) and several other economically important fish species. The bacterium can cause systemic infections in LYC, resulting in visceral granulomas disease (VGD) with high mortality in cultured populations. Despite the severity of this disease, the LYC industry lacks an effective vaccine for VGD. We have constructed a highly attenuated P. plecoglossicida mutant by deleting a virulence gene (tssD-1) from the wild-type (WT) strain XSDHY-P. We then investigated the safety and efficacy of the mutant strain Δ tssD-1 in LYC juveniles as a live attenuated vaccine candidate. LYCs were vaccinated with Δ tssD-1 by two intraperitoneal injections per fish, and then challenged with P. plecoglossicida XSDHY-P by the immersion route. Vaccination of Δ tssD-1 induced a significantly higher level of P. plecoglossicida -specific serum IgM and increased expression of CD8α and MHCIα, and resulted in a relative percentage survival of 86.3%. The safety of Δ tssD-1 was demonstrated because no mortality or clinical signs were found in a LYC group injected with a high dose (1.8 × 106 CFU per fish) of Δ tssD-1. This is the first report of a defined live attenuated strain providing protective immunity in LYC against P. plecoglossicida. • Attenuated Pseudomonas plecoglossicida strain Δ tssD-1 is safe and immunogenic as a fish vaccine. • Δ tssD-1 induces both humoral and cellular immune responses. • Δ tssD-1 provides protective immunity against P. plecoglossicida infection. [ABSTRACT FROM AUTHOR]