In aquaculture, the overuse of antibiotic could lead to antimicrobial resistance and destabilize host–microbiota homeostasis. Latilactobacillus sakei, belonging to the genus Latilactobacillus, was included in the list of bacteria that could be used in food in China in 2014. Increasing evidence demonstrated that its antagonistic capacity against a broad spectrum of pathogenic bacteria, indicating its promising potential for application in aquaculture. In this study, the protective effect of three L. sakei (JO12, JO26, JO35), isolated from the intestine of fish and shrimp, on mucosal injury caused by Aeromonas hydrophila in crucian carp under an oral challenge model was investigated. The result showed that compared with LGG, all three L. sakei strains alleviated A. hydrophila induced intestinal barrier damage and inflammation (downregulated intestinal TNF- α /IL-1β, upregulated IL-10, and reduced MyD88) in crucian carp. L. sakei JO35 delivered the greatest improvement in growth and feed efficiency. Compared with the model group, L. sakei JO26 and JO35 significantly decreased the levels of serum acid phosphatase (ACP) and increased intestinal lysozyme, whereas L. sakei JO12 lowerd serum ACP but exacerbated the elevation of intestinal AKP. Microbiome and transcriptome analysis revealed that the protective effect of L. sakei may be associated with the strain’s intestinal colonization capacity and its regulation of phagolysosomal competence (lysosome/phagosome, LAMP) and IgA barrier via pIgR (prominent with JO35).

The interaction between polyethylene microplastics and ciprofloxacin on inducing hepatotoxicity in Carassius auratus via the gut-liver axis.

Insight into greenhouse gas emission in freshwater aquaculture ponds in Jiangsu Province: Variation due to species used and ponds management practice.

An improved autotetraploid fish derived from the hybridization of gynogenetic homologous diploid crucian carp (♀) × autotetraploid carassius auratus (♂)

Lauric Acid (LA) and Glycerol Monolaurate (GML) are naturally present in several plant-derived oils, particularly coconut and palm kernel oil. These compounds have been widely applied in swine production owing to their proven antiviral activity against Porcine Reproductive and Respiratory Syndrome Virus (PRRSV), Porcine Epidemic Diarrhoea Virus (PEDV), and African Swine Fever Virus (ASFV). In this study, we investigated the potential of LA and GML as antiviral agents against Cyprinid herpesvirus 2 (CyHV-2), the causative agent of Herpesviral haematopoietic necrosis (HVHN), which poses significant challenges to China's freshwater aquaculture industry, particularly in crucian carp farming. Notably, no commercially available drugs or vaccines are currently approved for CyHV-2 infection. Our findings demonstrated that LA and GML significantly inhibit CyHV-2 replication and reduce viral infectivity. Further investigation into the antiviral mechanisms revealed that treatment with LA or GML disrupts the viral envelope structure, alters its physicochemical properties, and compromises virions' stability. Based on these results, we propose that LA and GML are promising natural antiviral agents for the control of CyHV-2 infection.

Aeromonas veronii (A. veronii) causes hemorrhagic septicemia and enteritis in aquatic animals, posing a threat to global aquaculture. Conventional vaccines are inadequate due to short immune duration, narrow antigenic spectrum, and insufficient commercialization. Outer membrane vesicles (OMVs), naturally secreted by Gram-negative bacteria, hold significant potential in vaccine development due to their enrichment with immunologically active components. This study aimed to characterize the biological properties of OMVs derived from the A. veronii TH0426 strain and evaluate their potential as a vaccine. Characterization revealed a diameter distribution of 10 to 300 nm. Proteomic analysis identified 76 proteins, including conserved antigens such as outer membrane channel-forming protein II (OmpII; 80% coverage) and outer membrane protein A (OmpA; 44% coverage). Evaluation in a crucian carp (Carassius auratus) model demonstrated that OMVs alone or combined with inactivated whole vaccine (Av) cells significantly enhanced serum antibody titers, serum bactericidal activity, and related immune enzymes (P < 0.05). Furthermore, they upregulated the expression of immune factors (TGF-β, TNF-α, IL-10, IL-1β) in tissues such as the liver and spleen (P < 0.05). In the challenge test, the relative percent survival of the OMV + Av group reached 66%. These results indicate that A. veronii OMVs possess application potential as vaccines, can effectively enhance the immune protection efficacy of aquatic animals, and provide novel insights for the development of next-generation vaccines against A. veronii.IMPORTANCEThis study demonstrated the biological characteristics and application potential of OMVs derived from the A. veronii TH0426 strain as a vaccine. OMVs exhibited favorable safety profiles in crucian carp and significantly enhanced serum bactericidal activity. Furthermore, OMVs displayed potent immunogenicity, effectively elevating the levels of key serum immune enzymes, immune factors, and IgM, thereby significantly boosting both the innate and adaptive immune responses in crucian carp. Critically, OMVs effectively enhanced the immunoprotective efficacy conferred by inactivated A. veronii whole cells, significantly improving the resistance of crucian carp to A. veronii infection. Future studies will explore the broader application value of OMVs and further investigate the feasibility of utilizing OMVs from the A. veronii TH0426 strain as a potential vaccine.

Allotetraploid fish produced by distant hybridization are valuable germplasm for the mass production of sterile triploids. The allotetraploid crucian-carp hybrid (4nAT, 4n = 200) is derived from the intergeneric cross between a female red crucian carp (Carassius auratus red var., 2n = 100) and a male common carp (Cyprinus carpio L., 2n = 100). However, after 33 successive generations, this lineage faces a critical bottleneck in maintaining male fertility. The present study aimed to develop new biomarkers for testicular development and characterize the associated functional gene expression profile in 4nAT. Following whole-genome resequencing and selection signature analysis of 15 male 4nAT individuals from each of the high-development group (HDG) and low-development group (LDG), ZSWIM7 (Zinc Finger SWIM-Type Containing 7), a gene implicated in reproductive development, was selected as a candidate for further fertility association studies. Seven SNPs were screened in the coding region of ZSWIM7 of 70 4nAT males; among these, SNP3 (c.23T/C) exhibited a significant correlation between genotypes and testicular development: individuals with the CT genotype showed a higher gonadosomatic index (1.17 ± 0.68 vs. 0.65 ± 0.50) and greater counts of mature spermatozoa (2537.67 ± 283.95 vs. 341.56 ± 121.66) compared to those with the TT genotype. Further quantitative PCR and immunofluorescence assays demonstrated that ZSWIM7 was highly expressed in the testis and specifically localized to the nuclei of early meiotic primary spermatocytes. Collectively, these results establish ZSWIM7 as a promising biomarker for 4nAT testicular development, offering a potential molecular tool for maintaining male fertility in allotetraploid fish breeding.

This study investigated the toxicological effects of chronic cadmium (Cd) exposure (0, 100, 300, and 500 μg/L for 28 days) on juvenile crucian carp (Carassius auratus), assessing impacts on gill tissue and gut microbiota using a multi-faceted approach. Histological analysis revealed concentration-dependent gill damage, including severe lamellar fusion and desquamation, with a parallel increase in apoptotic cells confirmed by TUNEL staining. Biochemically, Cd induced significant oxidative stress, as shown by decreased superoxide dismutase (SOD) activity, lowered levels of reduced glutathione (GSH) and total antioxidant capacity (T-AOC), and elevated malondialdehyde (MDA), a marker of lipid peroxidation. Gene expression analysis confirmed the activation of endoplasmic reticulum (ER) stress and pro-apoptotic pathways, with upregulation of chop and bax and downregulation of bcl2. Furthermore, Cd exposure profoundly restructured the gut microbiota, leading to pronounced dysbiosis and loss of microbial homeostasis. Collectively, these findings demonstrate that chronic Cd exposure induces gill damage in juvenile C. auratus through interconnected oxidative stress, ER stress, and apoptosis, while concurrently causing significant disruption to the intestinal microbial ecosystem.

Screening of several evaluation indicators for alkali resistance in fish.

Toxic effects of microplastic (polyethylene) exposure: Stress, immune responses and neurotoxicity in crucian carp, Carassius carassius.

Background: The Republic of Armenia is poor in water resources; therefore, fish farming is based on growing freshwater fish in artificial reservoirs. A special feature of the republic’s aquaculture is its focus on the breeding and cultivation of carp, as well as some species of predatory fish. Since sanguinicolosis especially affects cyprinid fish, the study of this disease is of great importance in the aquaculture of Armenia. Objectives: The objective of our study was to assist fish farmers in implementing effective measures for the prevention and treatment of sanguinicolosis, thereby preventing its further spread within the country. Methods: To identify the causative agent, parasitological and histological examinations were conducted on 200 fish specimens. Results: The results indicated that 42.5% of the examined fish were infected with sanguinicolosis. The cercariae exhibited a clear localization within the fish tissues, with lengths ranging from 0.16 to 1.6 mm. Morphological changes of a destructive nature were observed in the gills of the studied silver crucian carp specimens. Disruptions in the histological structure of the intestinal wall were also documented. Similar changes in the swim bladder were attributed to the direct negative impact of the parasite. Conclusion: The decline in fish populations in the pond farm specializing in the cultivation of crucian carp in the Armavir region of the Republic of Armenia is caused by infection with Sanguinicola sp. To determine the prevalence of the disease within the republic and identify the specific type of causative agent, it is deemed necessary to expand the scope and nature of the research.

Identification of an allotetraploid hybrid (Pengze crucian carp (♀) × Xingguo red carp (♂)) and its transcriptomic responses to herpesvirus infection

To address the significant wear of the stator rubber–metal rotor friction pair under the harsh downhole operating conditions of screw pumps, this study aims to increase the lubrication performance of the pair. Inspired by the morphological structure of crucian carp scales, a sector-shaped surface texture is designed and applied to the stator rubber. The impacts of the texture area ratio, included angle, and depth on the film pressure distribution and flow field are studied under complex downhole conditions by developing a finite element model of hydrodynamic lubrication for the friction pair featuring this texture and incorporating the cavitation effects. Furthermore, tribological experiments are conducted for verification. The obtained results demonstrate that the cavitation effect can significantly enhance the oil film pressure and load-carrying capacity of sector-shaped textures. Sector-shaped textures have higher performance than triangular, circular, and square textures. The optimal parameter combination consists of an area ratio of 30%, an included angle of 50°, and a depth of 10 μm. In this condition, the average oil film pressure reaches its maximum value and the most effective fluid dynamic pressure lubrication is achieved, leading to an optimized friction-reduction effect. Tribological experiments are conducted, demonstrating that the specimens with a texture area ratio of 30% exhibit the lowest coefficient of friction. The results obtained in this study provide a theoretical foundation for the bionic texture design of the stator rubber in high-performance screw pumps. The proposed approach facilitates the extension of pump inspection intervals while simultaneously reducing the development costs associated with oil fields.

The effects of biofilm formation of Hafnia paralvei mediated by quorum sensing on the meat quality and spoilage of crucian carp (Carassius auratus)

Cyprinid fish ubiquitin-specific protease 18 (USP18) downregulates the basal and induced interferon expression.

Indicator packaging film based on carboxymethyl cellulose sodium incorporating curcumin-loaded γ-cyclodextrin metal-organic framework for real-time assessment of fish quality.

The citizen science approach enables the collection of extensive ecological data while reducing time and cost, offering a valuable tool to address complex conservation challenges. However, its precision in monitoring morphologically similar freshwater fish species remains insufficiently explored. This study evaluates the effectiveness of citizen science in distinguishing between the critically endangered crucian carp ( Carassius carassius ) and the invasive gibel carp ( Carassius gibelio ), two closely related species often confused due to their similar appearance. The native crucian carp has experienced a sharp population decline in Central Europe and is currently classified as critically endangered in the Czech Republic. In response, the citizen science initiative, save the crucian carp was launched to map the species’ distribution and support its conservation and restoration. We assessed the project’s effectiveness using data submitted by 953 participants, which included current and historical occurrence records for both crucian and gibel carp. The analysis focused on species identification accuracy, public engagement, and the influence of media outreach on participation. Field verification of reported sightings revealed a 35% accuracy rate for crucian carp identification. A positive correlation was observed between respondents’ species identification quiz scores and the number of valid occurrence tips submitted. Participants aged 31–50 showed the highest engagement in conservation efforts. Notably, media campaigns significantly boosted public involvement, highlighting the importance of awareness-building in fostering biodiversity stewardship. Data collected through citizen science exhibited broader coverage and greater reporting regularity compared to records from the Nature Conservation Agency of the Czech Republic, underscoring the value of citizen contributions in shaping conservation strategies. Overall, this study illustrates the promise of citizen science as a scalable and impactful approach for monitoring and conserving threatened freshwater fish species.

The practice of rice–fish production dates back to the 15th–12th centuries BC in ancient China (Halwart and Gupta 2004). This symbiotic farming method offers numerous benefits for both rice cultivation and fish rearing. Fish thrive in a protected environment without the need for additional feed, while simultaneously contributing to the control of aquatic insect pests, soil aeration, and plant fertilisation. In Hungary, rice was cultivated on a scale of approximately 50,000–60,000 hectares prior to the 1960s, and carp production in rice fields was developed but declined with the onset of agricultural intensification. The subsequent use of insecticides temporarily halted this organic approach. However, in recent decades, increasing interest in organic rice production has led to a renewed focus on rice–fish systems and related research (Simon-Kiss 2001). In 2010 and 2012, experiments were conducted in Szarvas, Hungary, in which weatherfish ( Misgurnus fossilis ) and crucian carp ( Carassius carassius ) fingerlings were stocked in rice paddies for a two-month rearing period from July to September. The objectives of the study were to assess the growth and survival of these species and to evaluate the technology for future research and development. Following an unsuccessful preliminary trial with weatherfish in 2010, the experiment was repeated in 2012. Two paddy fields were stocked with fingerlings as follows: field "Monoculture": 250 crucian carp (total length [TL]: 13 ± 1.6 mm) field "Biculture": 250 crucian carp (TL: 13 ± 1.6 mm) and 400 weatherfish (TL: 15 ± 2.6 mm). field "Monoculture": 250 crucian carp (total length [TL]: 13 ± 1.6 mm) field "Biculture": 250 crucian carp (TL: 13 ± 1.6 mm) and 400 weatherfish (TL: 15 ± 2.6 mm). The fish adapted well to the agricultural environment and exhibited good growth under extensive rice-fish rearing conditions. Final body weights of weatherfish juveniles ranged from 4.1 to 18.9 g, while crucian carp reached 1.9–18.5 g. Survival rates varied between species, with weatherfish showing a survival rate of 10.5% and crucian carp survival ranging from 36.0% to 40.8%. No statistically significant differences (p &amp;lt; 0.05) were observed in final body weight or survival rates of crucian carp between the monoculture and biculture in rice fields. However, Fulton's condition factor was significantly higher (p &amp;lt; 0.05) in the monoculture system, indicating a slight negative effect on crucian carp growth performance when reared in biculture with weatherfish (Table 1). These preliminary observations suggest that rice fields may serve as effective sites for the ex-situ conservation of weatherfish and crucian carp. During the 45-day experimental period, both species exhibited strong performance and high growth potential. Further research is required to optimise the technology and improve the survival and harvesting efficiency of weatherfish. Rice fields represent suitable habitats for the extensive rearing of juvenile fish, while the biological control provided by these species can also support organic rice production (Suppl. material 1).

The crucian carp (Carassius carassius) occurs in two highly divergent phylogenetic lineages in Europe: the northern lineage, which is widespread across northern and central-eastern Europe and occurs in the Labe (Elbe) and Odra (Oder) river basins and the Danubian lineage, which is restricted to the Danube basin. the northern lineage, which is widespread across northern and central-eastern Europe and occurs in the Labe (Elbe) and Odra (Oder) river basins and the Danubian lineage, which is restricted to the Danube basin. The crucian carp from both phylogenetic lineages are naturally present in Czechia. However, probably due to intensive aquaculture and transfers by recreational anglers, fish from different lineages have become mixed in some areas, or particular phylogenetic lineages have been translocated to other watersheds. Although we cannot rule out natural admixture, the conservation of crucian carp should treat these lineages as separate conservation units. In response, a Regional Action Plan (RAP) was developed to preserve the current distribution of phylogenetic lineages in the Vysočina Region and to prevent further unnatural admixture. A citizen science approach ("Save the crucian carp” project) was used to find the remaining populations. Individual populations identified through citizen tips were selected for systematic site monitoring, and samples were collected for further analyses. The lineage (northern or Danubian) of these populations was evaluated using genetic analyses, and suitable populations for conservation were selected. As part of the RAP, we initiated the repatriation of genetically verified crucian carp populations. We distinguished the two lineages genetically and repatriated the populations to their corresponding locations within their respective watersheds. In total, five and seven northern and Danube populations were identified, respectively and three and five northern and Danube populations were repatriated, respectively, using source fish coming from identified populations. This study provides a comprehensive conservation approach for a declining wetland fish species. Although regionally restricted to the Bohemian-Moravian Highlands, the approach can be applied to other declining wetland species with similar ecology and genetic diversity. The findings emphasize the need for a complex, multi-approach assessment of species threats and highlight the importance of managing conservation actions based on scientific evidence (Suppl. material 1).

Successful invasive non-native fish species can cause enormous damage to native biodiversity. In the continental Europe, the introduction of the gibel carp ( Carassius gibelio ) has led to a decline in populations of the formerly widespread native crucian carp ( Carassius carassius ). Due to the decline of crucian carp populations the status of the specices changed from least concern to critically endangered in Czechia. Its populations have also declined in other countries where the gibel carp has become established. This contribution summarises the findings on the competitive displacement of native species by invasive species from both experimental approaches and historical trends. The recent findings demonstrated that the gibel carp utilises food sources much more efficiently than its native counterpart. The gibel carp are not only more aggressive and utilise shared resources faster, but also use plant material that is not available to the crucian carp as an effective food source. Finally, this contribution provides circumstantial evidence that the gibel carp is behind the transition from the relative abundance of large deep-bodied form of crucian carp to its near extirpation in Czechia, while large and deep-bodied gibel carp have taken over the reports of record angling catches in the genus Carassius . Taken together, the current findings strongly suggest that the crucian carp is being locally extirpated by the gibel carp. Due to the uneven competition between Carassius species, programmes to repopulate selected waters with crucian carp are necessary (Suppl. material 1).