Abstract:Algae have important strategic significance in optimizing food supply systems, promoting carbon sink fishery development, and enhancing marine economic competitiveness owing to their efficient biosynthetic capability, rich nutritional value, and ecological regulatory role. This article analyzes the current development status and main challenges faced by China's algae industry from the perspective of the "All-Encompassing Approach to Food,” and propose pathways and countermeasures to promote high-quality development of industry. Currently, China's algal industry has demonstrated steady overall growth, developing into a large-scale, intensive production system. Significant progress have been made in developing superior germplasm, expanding cultivation scales, upgrading products, and growing markets. However, some challenges still persist, such as limited innovation in stress-resistant germplasm, inadequate disease prevention and control systems, low levels of mechanization and automation in cultivation, short industrial chains, limited scientific research investment, outdated deep processing technology, and underdeveloped quality and safety supervision systems. To develop and expand the algal industry, it is necessary to strengthen policy support, accelerate breakthroughs in core and key technologies, and promote coordinated industry chains, green and low-carbon transformation, brand building, and global market integration.

Abstract:Algae, a blue resource with high nutritional value and environmental regulation functions, have cell walls and extracellular matrices rich in various functional groups. These characteristics enable algae to accumulate harmful heavy metals, such as lead (Pb), cadmium (Cd), arsenic (As), and mercury (Hg) easily, posing potential food safety risks. In this review, we cover the sources, accumulation mechanisms, and speciation of heavy metals in algae, focusing on the principles, effects, and applicability of major removal techniques, including physical (heat treatment, ultrasound, and high pressure), chemical (acid washing, chelating agents, and natural deep eutectic solvents), biological (fermentation, enzymatic hydrolysis, and microbial conversion), and adsorption methods. In addition, the potential applications of combined multi-technique approaches are explored. Current studies face challenges such as an insufficient understanding of speciation, difficulty in balancing efficient removal and nutrient retention, and the underdevelopment of green processing routes and industrial support systems. Future research should focus on multiscale mechanistic analysis, the development of green and mild processes, and the strengthening of industrial application frameworks, aiming to enhance the food safety of algae products and promote high-quality industrial development.

Abstract:To investigate the growth dynamics and carbon sequestration effects of kelp under different cultivation densities, this study used the traditional cultivation density of 100 ropes per raft (K0) in Sanggou Bay as the control group. During the tender stage of kelp (January), the cultivation density was reduced to 67 ropes per raft (K1) and 50 ropes per raft (K2), respectively. Methods such as on-site instrument monitoring, in-situ perforation sampling, UV-Vis absorption spectroscopy, and organic carbon analysis were employed to measure the light attenuation rate, absorption spectra of colored dissolved organic matter (CDOM) in surface seawater, elongation rate, and thickening rate of kelp blades in different density areas of Sanggou Bay. Differences in kelp growth dynamics under varying densities were analyzed, and carbon sequestration under different cultivation densities were estimated. The results showed that: (1) The light attenuation rates in the 0–1 m depth layer differed significantly among the three cultivation density areas. (2) The highest blade elongation rate in all three density groups occurred during the E3 stage (January–March), while the highest thickening rate appeared during the E4 stage (March–April). By the end of the experiment (June), the wet weight per individual kelp in the K1 and K2 groups was significantly greater than that in K0, and the total wet weight of kelp cultivation in the K1 group was significantly higher than that in the other two groups. (3) The absorption coefficient a(355) of colored dissolved organic matter (CDOM) at 355 nm in the K0 and K1 cultivation areas was significantly higher than that in K2 from March to June, while the SUVA254 values at the K0 and K1 stations in March and June were significantly higher than those at K2. By the end of the experiment, the total carbon pool contribution of the K1 group increased by approximately 15.19% compared with K0. The findings indicate that reducing kelp cultivation density to a reasonable level can significantly enhance kelp growth, yield, and the carbon sequestration of the cultivation system. This provides data support and technical references for developing models to enhance carbon sinks through large macroalgae cultivation in shallow seas.

Abstract:Pyropia haitanensis accounts for approximately 75% of total dried laver production in China. In recent years, advances in cultivation technologies and increasing economic returns, the expansion of cultivation areas has created an urgent demand for high-quality cultivars. The life cycle of P. haitanensis consists of two distinct phases, a filamentous sporophytic stage (conchocelis) and a foliose gametophytic stage, corresponding to indoor seedling propagation and offshore farming, respectively. The primary objective of artificial indoor seedling production is to generate conchospores and propagules for marine cultivation. Therefore, achieving the synchronized development of mature conchosporangial branches and the efficient release of conchospores are critical for ensuring high yield and quality in the subsequent blade stage. Currently, all five nationally certified P. haitanensis cultivars are pure lines established through the transplantation of free-living conchocelis into shells. Free-living conchocelis cultivation enables substrate-independent propagation, reduces dependence on shell substrates and spatial requirements, and minimizes contamination by epiphytic algae. However, these improved cultivars still face challenges related to asynchronous conchocelis maturation and low conchospore release efficiency—commonly referred to as the "difficulty in breeding elite strains" when using free-living conchocelis. Therefore, the key to overcoming this challenge is to precisely regulate the developmental process of free-living conchocelis following transplantation onto shells (seeding), with a particular emphasis on the coordinated control of conchosporangial branch formation and conchospore release. A systematic understanding of the underlying developmental dynamics and molecular regulatory mechanisms is essential for establishing a robust theoretical foundation to enable the accurate manipulation of high-quality conchocelis development. Previous studies identified diacylglycerol kinase (PhDGK1) as a key regulatory gene involved in the maturation of free-living conchocelis. In this study, conchocelis of strain WO84-1 were treated with 1  μmol/L of the diacylglycerol kinase (DGK) inhibitor R59022. Phenotypic differences between the control and treatment groups first became apparent on day 16 of ripening induction, and were evident on day 26. Samples from both groups were collected on day 0, days 16 and 26 for integrated, widely targeted metabolomic profiling and transcriptome sequencing. Metabolomic analysis revealed a significant differential accumulation of key metabolite classes, including amino acids and their derivatives, lipids, flavonoids, alkaloids, terpenoids, and nucleotides and their derivatives. KEGG pathway enrichment analysis indicated that these metabolites were predominantly associated with the biosynthesis of various plant secondary metabolites, pantothenate and CoA biosynthesis, glucosinolate biosynthesis, tyrosine metabolism, efferocytosis, zeatin biosynthesis, and flavonoid biosynthesis. By day 26 of ripening induction, the inhibitor-treated conchocelis exhibited elevated levels of lysophosphatidylcholine (LPC), lysophosphatidylethanolamine (LPE), and free fatty acids. Except for terpenoids, most amino acid- and nucleotide-related metabolites, along with alkaloids and flavonoids, showed decreasing trends in the treatment group at both time points. Weighted gene co-expression network analysis (WGCNA) clustered transcriptomic data into 15 modules. The turquoise and blue modules contained the largest number of genes (2,111 and 1,981, respectively), whereas the remaining modules contained 71–1,860 genes. Notably, genes within the red module exhibited low expression prior to ripening induction and were highly upregulated in the control group on days 16 and 26 but remained downregulated in the treatment group. KEGG enrichment analysis of genes in the red module revealed significant associations between DNA repair and replication pathways, including homologous recombination, base excision repair, mismatch repair, non-homologous end joining, DNA replication, and nucleotide excision repair. Integrated transcriptome–metabolome correlation analysis identified 22 annotated genes and 72 metabolites. Across both ripening induction stages, the treatment group showed significantly reduced levels of amino acids (and derivatives) and nucleotides (and derivatives), whereas LPC, LPE, and free fatty acids accumulated to substantially higher levels than in the control. DGK activity regulates the balance between phosphatidic acid (PA) and diacylglycerol (DG), thereby influencing the synthesis of LPC and LPE and modulating lipid metabolism. This regulatory function plays a crucial role in maintaining nuclear membrane integrity and ensuring stable expression of genes and transcription factors associated with conchocelis maturation. Through the metabolic intermediate acetyl-CoA, lipid metabolism intersects with amino acid metabolism, alkaloid biosynthesis, flavonoid metabolism, and nucleotide metabolism to form an interconnected metabolic network that coordinately regulates conchocelis development and maturation. Moreover, DGK inhibition disrupts the integrity of the membrane system and exacerbates oxidative stress. Treated conchocelis exhibited activation of multiple stress-related genes, including HSP20 and CAT. HSP20 is involved in abiotic stress responses in Pyropia, upregulation of CAT enhances reactive oxygen species scavenging, and glutathione S-transferase genes contribute to glutathione-mediated redox regulation. Therefore, DGK plays a significant role in conchocelis development and maturation by stabilizing membrane systems, enhancing antioxidant defenses, and maintaining cellular homeostasis under stressful conditions.

Abstract:Saccharina japonica, the most extensively farmed seaweed globally, is of great ecological and economic importance. Its applications extend far beyond food consumption, as it is widely utilized in industrial production, biofeed, and medical products, while also playing an important role in marine ecosystems. Its life cycle is characterized by an alternation of generations between haploid gametophytes and diploid sporophytes, with sporophytes typically produced through sexual reproduction. However, S. japonica also exhibits two alternative apomixis reproductive strategies, namely parthenogenesis and apogamy, which bypass fertilization. These asexual modes have attracted increasing attention, as they broaden our understanding of kelp developmental biology and provide new possibilities for germplasm innovation. Epiphytic microorganisms play critical roles in algal growth, morphogenesis, and disease resistance. However, it remains unclear whether sporophytes from different reproductive pathways harbor distinct microbial communities. To address this knowledge gap, we compared bacterial and eukaryotic epiphytic communities of five types of S. japonica sporophytes, representing different reproductive origins and growth states, to reveal differences in community composition, structure, and key biomarker taxa, and explore potential implications for asexual sporophyte development and cultivation. Sporophytes were induced from six female and 15 male gametophyte clones under controlled conditions, including normally growing and malformed parthenogenetic and apogamous sporophytes, as well as normally growing sexually reproduced sporophytes. After 75 days of culture, 39 sporophyte samples were collected. DNA was extracted from surface swabs, and the v3−v4 region of the bacterial 16S rRNA gene and the V4 region of the eukaryotic 18S rRNA gene were sequenced using Illumina NovaSeq 6000 platform. Sequencing reads were quality-filtered, merged, and clustered into operational taxonomic units at 97% similarity based on the SILVA reference database. Alpha diversity was evaluated using Chao1 and Shannon indices, and differences were tested using Student’s t-test. Beta diversity was assessed using non-metric multidimensional scaling (NMDS) based on Bray-Curtis distances and analysis of similarities (ANOSIM). Biomarkers were identified through linear discriminant analysis effect size (LEfSe) using a threshold LDA score ＞4 and P＜0.05. Alpha diversity analysis confirmed that malformed parthenogenetic sporophytes exhibited significantly higher bacterial richness and diversity than all other groups (P＜0.01). Sexual sporophytes showed the lowest alpha diversity in terms of both bacteria and eukaryotes. Apogamous sporophytes, regardless of morphology, generally had a higher diversity than sexual sporophytes, although the differences were not statistically significant. Beta diversity analysis revealed a clear separation of the five groups in the NMDS plots, with ANOSIM confirming significant dissimilarities for both bacterial (R=0.499, P=0.001) and eukaryotic communities (R=0.179, P=0.002). NMDS analysis further indicated that the five sporophyte growth types exhibited significant differences in species composition. In eukaryotic communities, normally growing sexually reproduced sporophytes exhibit the lowest richness and diversity, whereas malformed parthenogenetic sporophytes harbor the most structurally diverse epiphytic assemblages, which may be associated with their distinctive morphological and physiological statuses. Differential taxa among groups were identified using LEfSe and genus-level species composition analyses. Asexual sporophytes generally harbor more enriched bacterial taxa than sexual sporophytes. Malformed parthenogenetic sporophytes contained the highest number of biomarkers, whereas malformed apogamous sporophytes contained the lowest. At the genus level, Litorimonas emerged as the dominant bacterium across multiple groups and was particularly enriched in sexually reproduced sporophytes and malformed apogamous sporophytes. In contrast, the malformed parthenogenetic sporophytes were dominated by unclassified Cyanobacteria, with Litorimonas accounting for a small fraction of the community (3%). The consistent enrichment of Cyanobacteria, which possess an autotrophic capacity and produce antimicrobial metabolites, may partly explain their ecological success. In addition, Maribacter antarcticus was significantly enriched in malformed parthenogenetic sporophytes. Although its precise function remains unclear, its association with abnormal morphology warrants further experimental validation. Eukaryotic communities also exhibited notable variations. Most groups were dominated by Agarum clathratum, a kelp relative species capable of attaching to macroalgae and occasionally acting as a parasite under nutrient-rich conditions. However, malformed parthenogenetic sporophytes were enriched in Halomonhystera, a bacterivorous nematode-like taxon. Its occurrence coincided with higher bacterial loads in these samples, suggesting that host deformities and abundant microbial substrates provided favorable conditions for parasitic colonization. In summary, this study used high-throughput sequencing to systematically analyze the epiphytic microbial diversity of kelp sporophytes derived from sexual reproduction and apomixis. The results revealed significant differences in the microbial community structure between asexual and sexual sporophytes in both the bacterial and eukaryotic communities. Malformed parthenogenetic sporophytes exhibited the most distinct community structure. LEfSe analysis identified significantly different taxa, which enriched the understanding of microbial composition and structure in asexual sporophytes, and offered a solid foundation for future investigations into the interactions between asexual sporophytes and their epiphytic microbiota.

Abstract:Pythium porphyrae and Pythium chondricola, collectively known as red rot pathogens, pose a severe threat to nori (Pyropia/Porphyra) cultivation, causing substantial global economic losses. A critical factor underpinning their success as pathogens is their remarkable resilience and adaptability to fluctuating environmental conditions, which enable their persistent survival and infection. In our preliminary work, we annotated the key ectoine biosynthetic gene EctC, which is responsible for the synthesis of ectoine—an important stress-protective metabolite—from the Pythium porphyrae genome; notably, compared with homologs in terrestrial oomycetes, this gene shows a marked expansion Ectoine is a potent stress-protectant molecule that is well characterized in prokaryotes for its role in the osmoprotection and stabilization of macromolecules under various abiotic stresses, including high salinity, drought and oxidative stress. Its presence and potentially functional role in eukaryotic oomycetes, particularly in plant pathogens, represent a paradigm shift, as it was historically considered a prokaryotic-specific metabolite. This study aimed to functionally characterize the role of EctC from P. porphyrae (PpEctC) in oomycete growth, environmental stress tolerance, and pathogenicity. We employed a heterologous functional genomics approach using the established Phytophthora sojae transformation system. We generated a comprehensive set of transgenic strains in strain P6497 to investigate the function of EctC. Using the CRISPR/Cas9-mediated gene replacement strategy coupled with homology-directed repair (HDR), we successfully created a PsEctC knockout mutant (PsΔEctC-RFP), in which the native PsEctC gene was replaced with a red fluorescent protein (RFP) marker. We generated a heterologous complementation strain (PsΔEctC-PpEctC) by replacing PsEctC with the PpEctC gene from P. porphyrae. Additionally, we constructed a strain overexpressing PsEctC (Ps-oeEctC) and strain expressing PpEctC (Ps-hePpEctC) in the wild-type (WT) P. sojae background using a plasmid-based expression system. Successful gene editing, deletion, and altered expression levels of all transgenic strains were validated using PCR, qRT-PCR, and phenotypic screening. Phenotypic characterization under standard conditions revealed that the deletion of PsEctC significantly impaired mycelial growth, as evidenced by significantly smaller colony diameter of the PsΔEctC-RFP mutant compared with that of the wild-type and empty vector control (CK). Intriguingly, heterologous complementation of the PsΔEctC-PpEctC strain with PpEctC fully restored mycelial growth to that of the WT, demonstrating functional equivalence and cross-species compatibility of the P. porphyrae EctC in supporting basic P. sojae vegetative growth. In contrast, neither the knockout nor complementation significantly affected sporangia formation or zoospore production, except for an unexplained reduction in zoospore yield in the PsΔEctC-PpEctC strain. This suggests that EctC is primarily involved in hyphal expansion but not in the specific developmental reproductive stages under non-stress conditions. We then investigated the role of EctC in stress tolerance. Under high salinity stress (35% NaCl), the PsΔEctC-RFP knockout mutant exhibited a dramatic reduction in relative growth, highlighting its increased sensitivity to osmotic stress. The heterologous complementation strain (PsΔEctC-PpEctC) displayed a growth tolerance phenotype, which was statistically indistinguishable from that of the WT and CK, confirming that PpEctC could effectively restore osmotolerance. Strikingly, both the PsEctC overexpression (Ps-oeEctC) and PpEctC heterologous expression (Ps-hePpEctC) demonstrated superior growth under high-salt conditions, significantly outperforming the WT. This indicates that elevated EctC expression, whether from a native or heterologous source, confers a distinct advantage under osmotic stress. A similar trend was observed under alkaline pH stress (pH 9), in which the EctC knockout mutant was severely compromised, whereas the complemented and overexpression mutants maintained robust growth, underscoring the role of ectoine in pH stress mitigation. Given the critical role of reactive oxygen species in plant defense, we assessed the total antioxidant capacity of the transformants. We found that the PsΔEctC-RFP mutant showed a significant decrease in antioxidant capability. Conversely, both the Ps-oeEctC and Ps-hePpEctC mutants exhibited substantial enhancement in their antioxidant capacities, with the latter exhibiting a more potent effect. The complementation strain (PsΔEctC-PpEctC) showed a partial but significant recovery in antioxidant capacity compared to the knockout, although it did not reach that of the WT. This result shows a clear link between the EctC-mediated ectoine synthesis and pathogen’s oxidative stress defense system, which is crucial for countering host-induced oxidative bursts during infection. Pathogenicity assays on etiolated soybean hypocotyls provided compelling evidence for the role of EctC in virulence. The PsΔEctC-RFP knockout strain caused minimal lesions and showed a significantly lower relative in planta biomass than the WT, indicating severely attenuated virulence. Complementation with PpEctC (PsΔEctC-PpEctC) partially restored pathogenicity, leading to a higher biomass than the knockout although not to the WT levels. Most notably, heterologous expression of PpEctC (Ps-hePpEctC) resulted in hypervirulence, with significantly greater pathogen biomass recovered from the infected tissues than from the WT. The overexpression mutant (Ps-oeEctC) also showed enhanced virulence than the WT. These findings strongly suggest that EctC is a critical virulence factor and that its enhanced expression can potentiate pathogen infectivity and colonization ability, likely by bolstering resistance to host-imposed environmental and oxidative stresses. In conclusion, our study provides comprehensive functional evidence that the ectoine synthase gene EctC, particularly the PpEctC variant from P. porphyrae, plays a multifaceted and pivotal role in oomycete biology. It is integral for optimal mycelial growth, essential for tolerance to high salinity and alkaline pH, crucial for enhancing antioxidant capacity, and is a major determinant of pathogenicity. Successful heterologous complementation and the hypervirulent phenotype induced by heterologous expression confirmed functional potency of PpEctC. This study not only elucidates a previously uncharacterized stress adaptation mechanism in a destructive eukaryotic pathogen but also pinpoints EctC and the ectoine biosynthesis pathway as promising and novel targets for developing precise disease control strategies against red rot disease in nori aquaculture. Future work will focus on directly validating these findings in P. porphyrae upon the establishment of a robust transformation system.

Abstract:Sporeling malformation disease, characterized by abnormal cell proliferation and tissue disintegration, causes catastrophic losses in the seedling production of kelp Saccharina japonica. Previous studies have linked disease occurrence to environmental stressors (e.g., inadequate light exposure), the maturity of parental kelp (e.g., immature or overmatured), and alginate-decomposing bacteria, among others. Traditional culture-dependent approaches have failed to explain the complex pathogenesis of this disease, and its precise microbial etiology remains elusive. Recent advances in holobiont theory and our previous work suggest that dysbiosis of epiphytic microbiota, rather than individual pathogens, may drive sporeling malformation by disrupting host-microbe interactions and exacerbating disease severity. In the present study, we analyzed the diversity, structure, and functional profiles of epiphytic bacteria on sporelings with different malformation rates to obtain more data related to the relationships between epiphytic bacterial communities and the incidence of sporeling malformations using in situ sporeling samples. Through microscopic observations, in 2018, two groups of biological samples (Low and High groups) were collected from a workshop in a typical kelp seedling hatchery in Weihai, China. Epiphytic bacterial communities from low (~2%–6%) and high (~10%–12%) malformation groups were analyzed using 16S rRNA sequencing. Bioinformatic analyses (QIIME, USEARCH, LEfSe, and PICRUSt2) were used to assess community diversity, identify differential taxa, and predict functional profiles. Alpha diversity was lower in the high-malformation group. This indicated reduced bacterial richness. Community structure differed significantly between groups, with distinct shifts in dominant taxa. The low group demonstrated a higher presence of mutualistic and morphogenesis-associated bacteria. Meanwhile, the high group displayed more taxa associated with pathogenicity. The low group was more closely linked to metabolic and defense-related pathways. In contrast, the high group was associated with xenobiotic degradation and virulence-related functions. These findings highlight the importance of maintaining a healthy microbial community for sporeling growth and development and suggest potential targets for disease prevention and control. Future research should focus on changes in whole community functions using different omics methods and explore the interactions between the host, environment, and certain isolated bacterial strains in the context of disease development. This study not only enriches our understanding of the microbial ecology of kelp diseases but also has important practical implications for the kelp farming industry. Identifying key microbial taxa and functional pathways associated with disease may guide the development of microbial-based strategies for disease management, thereby contributing to the sustainable development of kelp cultivation.

Abstract:In China, the annual output of dried kelp is as high as 1.86 million tons; however, the harvesting process still relies heavily on manual labor, leading to low per capita efficiency and high labor intensity. Although foreign mechanized harvesting equipment exists, it is designed for long-line culture modes and is incompatible with the raft-type parallel culture system prevalent in China. The development of domestic semi-mechanized harvesting equipment faces challenges, such as poor raft adaptability and insufficient harvesting continuity, highlighting the need for synergistic innovation in both culture modes and equipment. To address these issues, we optimized mechanization-adapted culture modes and innovated key equipment components to develop a smaller-scale continuous harvesting system based on long seedling ropes, thus overcoming the efficiency bottleneck of traditional manual harvesting. First, a circuitous series-connected raft system for long seedling ropes was constructed by integrating 300 m continuous seedling ropes with 16 mm-wide quick-release buckles. This series structure preserves traditional culture density while facilitating reliable connections and rapid separation between the seedling ropes and rafts. Following a modular design approach, the core components (e.g., rectangular guiding devices, inclined conveyors, and low-damage stripping-cutting tools) were integrated with a hydraulic centralized control system, enabling single-person operation of continuous mechanized harvesting equipment. The stripping-cutting tool structure was innovatively optimized, with an outer blade diameter of 120 mm and inner blade diameter of 45 mm, and the allowable heave angle of the seedling ropes was increased to 55°. Dynamic simulation analysis using Ansys LS-DYNA software for emergency scenarios (e.g., hanging rope entanglement) revealed that the maximum equivalent stress was 405.04 MPa, far below the yield strength of the material, confirming structural strength reliability. Coupled with an umbrella-spoke-shaped seedling rope storage device (300 m capacity), stable and continuous mechanized harvesting of the entire raft was achieved. Trials of the equipment at a kelp harvesting site demonstrated that at a harvesting line speed of 9.36–14.82 m/min, the system achieved 100% kelp-harvesting completeness with no seedling rope breakage. Single-raft harvesting time ranged from 27‒36 min, and the per capita harvesting rate reached 2 t/(h·person), twice that of traditional manual labor. Only four workers are required to complete the entire process without heavy physical labor, addressing the issues of frequent start–stops and high manual assistance intensity associated with traditional equipment. The system enables integrated operations such as seedling rope separation, continuous dragging, stripping-cutting harvesting, and seedling rope storage. The novel harvesting system proposed in this study addresses the technical bottlenecks of poor raft adaptability and low harvesting continuity by establishing a collaborative solution for mechanization-adapted culture modes and equipment. The modular design accommodates operational needs across different scenarios, and the doubled efficiency effectively alleviates labor shortage pressures, providing equipment support for the large-scale promotion of mechanized harvesting in China's major kelp-producing regions. Beyond the kelp industry, the modular design concept and low-damage harvesting technology offer references for the mechanized harvesting of other large algae, contributing to the intelligent upgrading of marine aquaculture equipment.

Abstract:Large-scale algal cultivation plays a vital role in the aquaculture industry in China. Saccharina japonica, the predominant species, accounted for 61.4% of the national total algal aquaculture output of 3.0294 million tons in 2024. The harvest window for S. japonica is notably brief, typically lasting only to 2‒3 months. Freshly harvested kelp has a very high moisture content (approximately 90% wet basis), necessitating immediate primary processing to prevent spoilage and facilitate storage and subsequent processing. The two primary traditional pretreatment methods are sun-drying and salting. Although salting is efficient and weather-independent, making it suitable for large-scale processing, sun-drying remains a crucial cost-effective method in regions with ample sunlight owing to its near-zero energy consumption. Sun-drying is mainly categorized into hang-drying and pavement drying. The practice of hang-drying is space efficient and yields cleaner products; however, it has several disadvantages, including longer drying cycles, severe product curling, and polysaccharide leaching. Pavement drying offers a higher drying efficiency, but traditional direct sand-beach spreading leads to significant sand contamination, relegating its use primarily to chemical feedstocks or abalone feed. Improved pavement-drying techniques, such as the use of pebble beds or polyethylene nets, have demonstrated the potential to produce high-quality dried kelp but remain labor intensive. The fundamental challenges in traditional sun-drying methods include high labor intensity and low operational efficiency, which severely constrain industrial-scale production. This issue is further exacerbated by the declining fishery labor force. Consequently, mechanization of the sun-drying process has become an urgent priority. Significant research efforts have been directed towards mechanizing hanging-drying, leading to the development of various systems, such as automatic lifting and hanging systems, multi-layer tray drying systems, and long-line continuous drying systems. These innovations have successfully mechanized the practice of hang-drying. In contrast, there are few studies of mechanized solutions geared towards pavement drying. Existing techniques involve fixed net frames that require laborers to traverse long distances for spreading and retrieval, thus failing to alleviate the core issue of labor intensity. Furthermore, a critical technological bottleneck for efficient and continuous mechanized pavement drying is the conveyor system. Although chain-and-net structures offer reliable performance, their prohibitively high manufacturing costs limit their large-scale application. In this study, we aimed to develop a novel continuous conveyor-type kelp pavement-drying equipment to overcome the limitations of existing methods. The primary objectives were to significantly reduce labor intensity, achieve automated operation for both spreading and retrieval, ensure high drying quality without sand contamination, and provide a cost-effective alternative to expensive chain-based conveyor systems, thereby facilitating widespread industrial adoption. A prototype "Continuous Conveyor Net for Pavement-Drying of Kelp" was designed and fabricated. The core design incorporates a steel wire rope net belt as the conveying medium and an automated cover net system. The key components include a synchronous anti-slip device with dual-groove pulleys and steel wire ropes, the rope-net structure, a tail drum assembly, dual-roller support frames, and a cover net mechanism. A structural analysis was conducted by focusing on the stress distribution within the steel wire ropes and the tensioning mechanics of the drum assembly. Extensive pilot-scale trials were performed to evaluate the system performance. A 50 m long prototype was tested under varying mass loads (20‒100 kg) to measure the resultant dragging tension on the steel wire ropes. The synchronization performance of the dual-groove pulley anti-slip device was quantified by measuring the relative displacement between two steel wire ropes during operation. The wind-resistance capability of the automatically deployed cover net was rigorously tested. Pilot-scale trials yielded critical operational data and validated the effectiveness of the design. The dragging tension on the steel wire ropes in the 50 m prototype correlated linearly with the applied load, ranging from 836.43‒1068.3 N for masses between 20‒100 kg. Regression analysis of these data produced a predictive trendline formula (y = 2.8984x + 778.46), which serves as a foundational basis for configuring the dragging force and motor power requirements for scaling the equipment to longer lengths, such as a projected 300 m system. The synchronous anti-slip device demonstrated exceptional performance, maintaining the relative displacement between the two steel wire ropes within a tight tolerance of ±4 mm throughout the operation, ensuring smooth, synchronized movement without slippage and guaranteeing operational reliability. The automated cover net system proved highly effective, withstanding wind speeds of up to 13.8 m/s, thereby effectively preventing wind from dislodging or disrupting the drying kelp and eliminating a major source of product loss and contamination. Operationally, the equipment enables a stationary work mode. The laborers remain at a fixed location to place fresh kelp onto the net belt, which then automatically conveys the material distally until the entire length of the belt is evenly covered. The cover net is deployed automatically. After drying, the process is reversed, and the dried kelp is conveyed back to the starting point for easy collection. This eliminates the need for workers to walk long distances across large drying fields, fundamentally reducing the labor intensity. Compared to hang-drying, pavement-drying achieved with this equipment resulted in superior product flatness, faster drying rates, and crucially, complete absence of sand or other particulate contaminants due to the elevated net belt, leading to a significant enhancement in the final product quality. A key economic advantage was confirmed: the manufacturing cost of the critical components of the steel wire rope net belt structure is substantially lower than that of an equivalent chain-and-net structure. For a 300 m system, this cost reduction was quantified at approximately 111,000 Yuan, underscoring the excellent cost effectiveness and potential for large-scale implementation. In summary, we successfully developed and validated a continuous conveyor net pavement-drying system that effectively addresses the major challenges associated with traditional kelp pavement drying. The system offers significant advantages by integrating a steel wire rope net belt with a synchronous anti-slip device and an automated wind-resistant cover net. It achieves a substantial reduction in labor intensity through automated conveying, enhances the drying quality and efficiency, prevents sand contamination, and offers a cost-effective solution superior to chain-based alternatives. These findings provide a reliable technical and theoretical foundation for the design and power configuration of large-scale systems. This technology represents a promising and practical solution for the mechanized, high-quality pavement-drying of kelp, with strong potential for widespread application and a positive impact on the industry.

Abstract:Laminaria japonica, a large perennial brown alga of medicinal and culinary value, thrives in cold marine environments. As a principal economic seaweed species in China, it is characterized by high productivity and exceptional nutritional density. However, the characteristic marine odor substantially compromises consumer sensory acceptance, posing a major constraint on the value-added processing and industrial exploitation of L. japonica-based products. Consequently, the investigation of efficient deodorization techniques and their underlying mechanisms is of considerable importance. The primary odorants of L. japonica are ketones, aldehydes, and alcohols. These volatile compounds can be effectively separated, identified, and quantified using analytical techniques, including gas chromatography-ion mobility spectrometry (GC-IMS), which integrates the superior separation capability of gas chromatography with the rapid detection characteristics of ion mobility spectrometry. This combined technique offers high sensitivity, operational simplicity, and cost-effectiveness and requires minimal sample preparation, making it extensively applicable for the analysis and identification of food flavor compounds. Current deodorization methods for L. japonica include physical, chemical, and biological approaches. Physical methods, such as masking, adsorption, and encapsulation, have limited deodorization efficiency. Chemical methods, including acid-base treatments or antioxidant immersion, although effective, often introduce chemical residues that are difficult to eliminate. Biological deodorization is an environmentally friendly, mild, and efficient approach that utilizes microbial metabolism to convert the odorous substances in L. japonica into non-odorous macromolecules. However, most existing biological deodorization processes use L. japonica pulp or fragments as raw materials, which impedes subsequent refining. This study used whole L. japonica blades for microbial fermentation-based deodorization to establish a superior raw material foundation for downstream processing and address this limitation. To investigate the sources of off-odors in salted L. japonica and the regulatory effects of yeast fermentation on its flavor profile, intact salted L. japonica (without comminution) was used as raw material. Three yeast strains, Pichia kluyveri CICC 32844, Saccharomyces cerevisiae CICC 32883, and Wickerhamomyces anomalus CICC 33313, were selected for fermentative deodorization of both raw and cooked salted L. japonica. The sensory evaluation results indicated minimal and non-significant differences in texture and color among the samples fermented with the three strains. However, significant variations in deodorization efficacy were observed. W. anomalus demonstrated the highest deodorization efficiency and overall performance for raw salted L. japonica, whereas Saccharomyces cerevisiae exhibited optimal deodorization and comprehensive effects on cooked salted L. japonica. W. anomalus and S. cerevisiae were the most suitable strains for raw and cooked salted L. japonica, respectively. The two selected strains were used for flavoring and fermenting salted L. japonica. The volatile flavor compounds in the samples subjected to different treatment conditions were qualitatively and quantitatively analyzed using GC-IMS, enabling characterization of alteration in the flavor profile and comparison with commercial L. japonica products. The relative odds activity value (ROAV) method was used to comprehensively evaluate the flavor characteristics and identify key compounds across different sample groups. The results revealed that the off-odors of salted Laminaria japonica were predominantly attributed to aldehydes and ketones. Among these, 1-octen-3-one was identified as the most potent odor marker, whose mushroom and earthy notes contributed more significantly to the characteristic marine odor than traditionally recognized aldehydes, such as (E)-2-nonenal and propanal. Although thermal processing can generate pyrazine flavor compounds, such as 2,3,5-trimethylpyrazine, via the Maillard reaction, their actual flavor contribution remains minimal (ROAV＜0.1), demonstrating limited masking effects. After fermentative flavoring, the sensory quality of salted L. japonica significantly improved. In raw salted L. japonica, the process generated compounds such as isovaleraldehyde and propyl acetate, which synergistically masked the off-odors. In cooked salted L. japonica, fermentative flavoring produced isovaleraldehyde and alcohols, including n-hexanol, which effectively concealed the marine odor while increasing the diversity of aroma compounds. Comparative flavor analysis of the experimental samples and the identified commercial products identified isovaleraldehyde, phenylacetaldehyde, p-methylbenzaldehyde, 1-octen-3-one, acetylpyrazine, and diallyl disulfide as the key flavor compounds common to all samples. Among these, isovaleraldehyde imparted a distinct chocolate and fatty aroma to L. japonica samples, contributing significantly to their overall flavor profile. Notably, significant differences in overall flavor composition were observed between the experimental and commercial samples. Following the fermentative flavoring treatment, 1-octen-3-one was no longer the dominant contributor to the flavor profile, demonstrating the feasibility and effectiveness of the fermentation-based flavor modulation process developed in this study.In this study, qualitative and quantitative analyses of the key flavor compounds in raw salted L. japonica and its seasoned or fermented derivatives were performed. By systematically investigating compositional differences and dynamic changes in volatile profiles before and after yeast-mediated fermentation, and by comparing them with commercial products, L. japonica products with distinctive flavor characteristics were successfully developed. This study reveals the dynamic transformation of flavor compounds during microbial fermentation, and offers novel strategic insights for the development of seaweed products and the optimization of microbial deodorization technologies.

Abstract:Cognitive abilities of animals are a focal topic in contemporary behavioral ecology and comparative psychology. Fish are the only vertebrate clade that is fully adapted to aquatic environments, and display distinctive adaptations in perception, information processing, and behavioral decision-making. The aquatic habitats on which they depend differ markedly from terrestrial systems regarding physical structure, light regimes, chemical cues, and ecological pressures. These differences have shaped the unique cognitive traits and behavioral strategies of fish. A systematic understanding of the cognitive performance of fish and the behavioral and ecological mechanisms underlying it explains the evolutionary trajectories and adaptive significance of animal cognition and provides theoretical and applied guidance for sustainable fisheries management, the optimization of aquaculture practices, improvements in the welfare of farmed fish, and informs discussions on ethical handling of animals. This review incorporates the research on fish cognition, emphasizing the advances in four domains: learning and memory, spatial cognition, perceptual discrimination, and social cognition. We further summarize commonly used experimental paradigms and methodological approaches in studies of fish cognition and, on this basis, critically assess the limitations and challenges of prior studies and priorities for future research. This study aims to deepen the theoretical understanding of fish cognition and broaden its practical applications in aquaculture and the management of fishery ecosystems.

Abstract:In recent years, with the popularization and advancement of animal welfare concepts, the research scope has expanded from terrestrial to aquatic organisms. Related issues have garnered increasing attention from government agencies, animal protection organizations, researchers, and aquaculture practitioners. Habitat conditions, aquaculture practices, fishing methods, sales processes, and artificial stocking can potentially affect fish welfare. Based on an overview of the concepts and current progress in fish welfare research, this study summarizes the main factors affecting fish welfare. These encompass intra- and interspecific interactions, environmental conditions such as water quality, stocking density, and nutritional supply, as well as key production management measures including genetic breeding, live transport, grading, and slaughter. This study further reviews relevant evaluation indicators for fish welfare, including (1) behavioral metrics such as swimming activity, exploration, aggression, schooling, respiratory rate, feeding, stereotyped behaviors, and escape attempts; (2) physiological and biochemical parameters such as neuroendocrine regulation, oxidative stress, and immune and hematological responses; and (3) emerging and integrated assessment approaches, including methods based on cognitive bias tests and lateralization analysis, as well as other comprehensive evaluation methods and welfare assessment tools. However, the limitations of the current fish welfare research were highlighted and future work, grounded in species conservation and ethical considerations to systematically address fish welfare issues across different scenarios, was emphasized. Fully respecting the ecological habits of fish was proposed, focusing on safeguarding their natural behavioral expressions and maintaining their healthy physiological states. In addition, establishing a fish welfare advancement mechanism underpinned by policy and regulations, supported by scientific research, and aimed at public participation, to achieve coordinated development of fisheries production practices and fish welfare protection was emphasized. This study provides a theoretical basis for establishing a standardized fish welfare assessment framework and promoting welfare-oriented, healthy aquaculture practices.

Abstract:Crustaceans are an economically important group in global aquaculture and fisheries. Whether these animals possess the capacity for pain perception has long been a subject of controversy and a focal issue in neuroscience and animal welfare research. The traditional view holds that crustaceans exhibit only nociceptive reflexes and cannot perceive pain. However, accumulating evidence indicates that their responses to harmful stimuli are far more complex than previously assumed. This review summarizes recent advances in crustacean pain perception research, beginning with the conceptual distinction between nociception and pain, and systematically analyzes evidence from behavioral, physiological, and neurobiological perspectives. Current research has shown that crustaceans display complex behavioral patterns, including protective motor responses, motivational trade-offs, and rapid avoidance learning. Harmful stimuli can trigger sustained stress responses and local anesthetics and sedatives have the potential to suppress pain-related behaviors. Neurobiological studies have confirmed the existence of various nociceptors and their capacity to integrate information into the central nervous system. However, existing studies still show limitations in the integration of evidence chains, consistency of experimental design, and methodological rigor. This review provides a theoretical reference for a deeper understanding of crustacean pain perception and offers a basis for improving animal welfare assessment and the sustainable development of fisheries.

Abstract:Anthropogenic noise generally refers to various types of noise generated by human activities and released into the environment, including mechanical operation sounds, ship navigation noises, engineering blasting sounds, and other similar acoustic emissions. As a secondary pollutant introduced into natural environments through human activities, underwater acoustic propagation characteristics and the ecological impacts of anthropogenic noise have emerged as critical interdisciplinary research focuses at the intersection of marine environmental science and aquatic biology. Unlike terrestrial environments, industrial noise in aquatic systems exhibits long-term, cumulative, and cross-habitat propagation characteristics, thereby imposing significant negative impacts on fish and other aquatic organisms in underwater ecosystems. With the acceleration of globalization, the intensity of marine development has increased exponentially. According to the Food and Agriculture Organization (FAO, 2024), the global merchant fleet tonnage has grown by 75% over the past two decades, offshore wind power capacity has expanded at an annual rate of 22%, and intensive aquaculture production now accounts for 52% of the total fishery output. The noise fields generated by these activities, ranging from ship-propeller cavitation to pile driving for offshore infrastructure and mechanical vibrations in aquaculture facilities, have significantly altered the marine soundscape. Background noise levels in some coastal waters have increased by 15–20 dB since the 1960s, driven by the cumulative effect of continuous low-frequency rumbling from shipping and intermittent high-energy pulses from construction activities. This drastic transformation of the underwater acoustic environment poses multidimensional stresses to fish, which rely heavily on sound for essential life processes. Physiologically, prolonged noise exposure disrupts sensory systems, causing microstructural damage to swim bladders, which are critical for sound resonance, and induces apoptosis of auditory hair cells in the inner ear, thereby impairing sound detection. Behaviorally, noise interferes with navigation, communication, and survival strategies; coral reef fish struggle with mate recognition and predator avoidance because ambient noise masks species-specific acoustic signals. At the population level, these effects cascade into a decline in local species abundance and alterations in community structure. The rapid expansion of human activities, including global shipping, offshore engineering, recreational boating, and industrial aquaculture, has brought the issue of anthropogenic noise affecting fish welfare to the forefront of attention for environmental organizations, government agencies, research institutions, aquaculture practitioners, and consumers. In recent years, the scientific community has responded to a growing body of research reflecting a heightened awareness of this ecological challenge. However, current research remains constrained by notable limitations. The majority of studies focus on single model species subjected to acute noise exposure in controlled laboratory settings, measuring short-term behavioral changes or physiological indicators, such as elevated serum cortisol. While such studies provide insights into species-specific threshold responses, there is a lack of systematic discussion from the perspective of fish habitat classification regarding the differences in responses among different ecological fish types to noise. Accordingly, this study systematically collates and analyzes a large body of relevant literature through bibliometric analysis and further employs the VOSviewer visualization tool to conduct a multidimensional quantitative analysis of 283 documents. This process constructed a keyword co-occurrence network, a national collaboration map, and an institutional distribution map, with the goal to provide visual support for interpreting research progress and outline advances in on the study of fish responses to anthropogenic noise. This study also discusses the current research status of how anthropogenic noise in natural and aquaculture environments affects fish welfare parameters such as growth, physiology, and behavior. In natural environments, fish exhibit altered swimming behaviors. For example, when ships approach, they change their swimming direction, make rapid turns, or display avoidance behaviors. Recent studies have also revealed that fish behavioral responses to anthropogenic noise extend to anti-predation and foraging activities. From a physiological perspective, intermittent high-level ship noise induces acute stress responses in coastal marine fish, manifesting as, for example, sudden increases in serum cortisol concentration. In terms of reproductive behavior, traffic noise masks the acoustic signals emitted by male fish during the breeding period in freshwater streams, disrupting the ability of females to extract information about males from these signals and negatively affecting successful mating. At the survival capacity level, ship traffic restricts the activity range of marine fish, potentially causing them to miss food resources and thus affecting their long-term survival. In aquaculture environments, fish in marine cages, lake enclosures, and land-based industrial farms are exposed to persistent anthropogenic noise. Considering recirculating aquaculture systems as an example, the low-frequency vibrations and mechanical noise generated by equipment operation have been proven to stress the growth performance and immune function of freshwater fish such as rainbow trout. The findings of this study will support public awareness, aiding in formulating guiding policies, promoting interdisciplinary development in related fields, and driving technological innovation. By unraveling the complex relationships between anthropogenic noise and fish responses, this study seeks to facilitate the coordination between human activities and the underwater soundscape environment on which fish depend for survival, improve fish welfare, and achieve a win-win situation between economic benefits and ecological sustainability.

Abstract:With the rapid development of aquaculture globally, the welfare of farmed aquatic animals has become a growing concern. As an emerging environmental stressor, underwater noise pollution has garnered major attention in ecotoxicological research because of its impact on the auditory system and behavioral patterns of fish. The large yellow croaker (Larimichthys crocea), a representative species of the family Sciaenidae, exhibits high auditory sensitivity. The impulsive low-frequency noise (800–1 200 Hz) generated by construction activities (e.g., engineering drilling) in coastal aquaculture zones substantially overlaps with the most sensitive auditory frequency range (400–600 Hz) of this species, potentially causing hearing impairment and behavioral stress. Although previous studies have demonstrated that low-frequency acoustic stimuli affect physiological indicators in L. crocea, the direct evidence of hearing damage and the regulatory effects of body size remain insufficiently explored. This study aims to address these gaps by providing data that can be used to optimize aquaculture environments, enhance fish welfare, and establish noise management standards. Juvenile large yellow croaker from the Rudong Institute in Jiangsu were subjected to short-term noise exposure experiments in a 6 × 1.5 × 1.5 m concrete tank. The noise source was an engineering drill (128T AVT HUMMER) operated 3–10 m from the tank. Construction activities were conducted daily from 07:00 to 11:00 for 10–20 min per session, at 30-min intervals, over three days. A Reson hydrophone (TC4032) and Brüel & Kjær data acquisition module were used to record the sound pressure level and particle motion of the construction noise. The underwater construction noise was broadband in nature, with a dominant spectral peak at 840 Hz and a corresponding sound pressure level of 143.59 dB. Spectral analysis revealed that the primary frequency range of the noise was 800–1,200 Hz, with intensities 40–60 dB higher than the baseline noise level in the aquaculture tank (60–80 dB). Auditory evoked potential (AEP) experiments were conducted in a 50 cm diameter cylindrical tank using a UW-30 underwater speaker to deliver pure-tone stimuli (100–1,200 Hz, 130–60 dB, 3 dB steps). The AEP signals were recorded using a TDT (Tucker-Davis technologies) auditory electrophysiology workstation. The experiment consisted of two phases: pre-exposure (control group) and post-exposure (treatment group). Each fish was tested at 10 frequencies (100–1200 Hz) to determine auditory thresholds. Generalized linear mixed models (GLMMs) were used to analyze the interaction effects of auditory thresholds on frequency, body weight, and noise exposure. Fixed effects included frequency, body weight, and group (control/treatment), whereas random effects accounted for individual variability. Post-exposure auditory thresholds in L. crocea increased significantly (P＜0.001), with the greatest threshold elevation observed in the most sensitive frequency range (400–600 Hz), where the average hearing loss reached 11.42 dB. At 500 Hz—the frequency of peak auditory sensitivity in juvenile large yellow croaker—the mean pre-exposure hearing threshold was (75.75±4.14) dB. Following noise exposure, a mean hearing loss of 11.14 dB was observed, indicating substantial damage to critical communication frequencies. At 300 Hz and 400 Hz, body weight exhibited a significant positive correlation with auditory thresholds (Spearman’s r = 0.673, P = 0.033; r = 0.753, P = 0.012), indicating that larger individuals had reduced auditory sensitivity. The GLMM model revealed a significant interaction between body weight and noise exposure (P = 0.004), with the positive effect of body weight on auditory thresholds being more pronounced in the noise-exposed treatment group (noise-exposed). In this study, we evaluated the effects of construction noise exposure on the auditory thresholds of L. crocea and explored the regulatory role of body size in auditory sensitivity. By integrating auditory evoked potential techniques and GLMMs, we elucidated the damage characteristics and potential mechanisms of construction noise in the auditory system of the fish, providing a scientific basis for noise management in aquaculture environments. The overlap between the dominant frequency of construction noise (840 Hz) and the most sensitive auditory range of the fish (400–600 Hz) resulted in the greatest hearing loss at critical communication frequencies, potentially disrupting acoustic communication and environmental perception. Larger individuals exhibited reduced auditory sensitivity in mid-frequency ranges (300–400 Hz), a pattern consistent with findings in other species (e.g., Scorpaenodes barbatus), which is likely linked to auditory system development and sound propagation efficiency. Noise-induced hearing impairment and stress behaviors may reduce foraging efficiency and reproductive success in L. crocea, ultimately affecting aquaculture yield. Furthermore, the observed cumulative effects of noise exposure highlighted the need to address the long-term risks of chronic noise pollution. This study focused on juvenile fish; future research should be extended to adults and reproductive-stage individuals to assess differences in developmental sensitivity. Additionally, experiments conducted in closed tanks differ from those conducted in open-sea net-cage environments, necessitating validation under natural conditions. Long-term studies should incorporate histological analyses (e.g., inner ear hair cell damage) and behavioral ecological metrics to comprehensively evaluate the population-level impacts of noise.

Abstract:Lipopolysaccharide (LPS), a major component of Gram-negative bacterial cell walls, is commonly used as an inducer of intestinal inflammation in animals, but research on its effects in aquatic animals remains limited. This study focused on blackrock fish, Sebastes schlegelii, an important mariculture species in Shandong Province, using intraperitoneal LPS injection to establish an enteritis model. Evaluation included histopathology, immunoenzymatic activity, tight junction proteins, and inflammatory factor gene expression. The control group received sterile phosphate-buffered saline (PBS), while experimental groups were given low-dose (5 mg/kg LPS), medium-dose (10 mg/kg LPS), and high-dose (15 mg/kg LPS). Each group consisted of three replicates, each with 30 fish (initial body weight 85.3±1.7 g). Samples were collected at 0 h, 6 h, 12 h, 24 h, 48 h, 72 h, and 96 h post-injection. The results showed that LPS at 5–15 mg/kg effectively induced intestinal structural lesions, inflammatory responses, and oxidative stress, with severity positively correlated to dose. Examination results indicated that the incidence of intestinal damage was 70% in the low-dose group and reached 100% in both the medium-dose and high-dose groups. Histopathological observations revealed intact intestinal structure in controls, whereas LPS groups showed dose-dependent lesions, primarily inflammatory cell infiltration, villi breakage, lysis, and detachment. In the low-dose group, some fish displayed severe villi structural damage, occasional epithelium damage, intact lamina propria, and infiltration of inflammatory cells into the lamina propria and submucosa. In the medium-dose and high-dose groups, fracturing and detachment were observed. The damage to the epithelium and lamina propria was intensified, and infiltration of inflammatory cells was more pronounced. Notably, the high-dose group showed evident villi detachment and a significant reduction in goblet cell lysis. Antioxidant enzyme assay showed that after LPS stress, SOD activity in the high-dose group was significantly reduced versus the control group at 6 h (P＜0.05). Additionally, SOD activity in the medium-dose group was significantly lower than the control group at 12 h (P＜0.05), and in the low-dose group at 24 h (P＜0.05). The overall trend of SOD activity in all experimental groups decreased then increased, remaining significantly lower than that of the control group's at 24 h post- stress (P＜0.05). MDA activity differed highly significant between the high-dose group and control group from 12 h post-injection (P＜0.001), and the low-dose group differed at 12 h and 24 h (P＜0.05), but no significant differences remained at 96 h. ACP activity in all experimental groups was significantly lower than the control group at 6 h (P＜0.05). It reached its lowest point at 12 h in the medium-dose and 24 h in the high-dose group, with no significant difference by72 h (P＞0.05). AKP activity in the high-dose group was significantly lower than the control group at 6 h (P＜0.05), and in all experimental groups at 12 h (P＜0.05). AKP activity in the low-dose and medium-dose groups recovered by 48 h, showing no significant difference from the control group. LPS injection altered the expression of inflammation-related genes and tight junction protein genes to varying degrees. The overall level of IL-1β gene expression increased then decreased; specifically, in the high-dose group it was significantly higher than the control group at 6 h (P＜0.05). Additionally, the intestinal expression level of IL-8 in all experimental groups was significantly elevated versus the control group at 6 h (P＜0.05), remaining significantly higher in the high-dose group at 96 h (P＜0.001). The IL-10 gene expression level in the high-dose group was significantly lower than the control group at 6 h (P＜0.001), and decreased in the low-dose and medium-dose group at 12 h (P＜0.05). After LPS stimulation, NF-κB expression showed an increasing-and-decreasing trend; it was significantly higher in the high-dose group versus the control at 6 h (P＜0.05), and in the low-dose and medium-dose groups at 12 h, 24 h, and 48 h (P＜0.05). In the high-dose group, the expression of occludin and ZO1 genes was significantly down regulated at 6 h (P＜0.05), although not at 96 h. In the medium-dose group, their expression was significantly lower at 12 h and 24 h (P＜0.001). The relative expression of the ZO1 gene in the low-dose group was significantly lower than that in the control group at 24 h (P＜0.05), with no statistically significant differences at other time points. These gene expression changes indicate that LPS can induce an inflammatory response in S. schlegelii. This study demonstrated that LPS induces intestinal tissue damage, compromises antioxidant capacity, and causes abnormal expression of inflammatory-related genes in S. schlegelii. Consequently, LPS functions as a reliable inducer for establishing intestinal inflammation models in S. schlegelii, thereby providing a robust foundation for further in-depth investigation into the pathogenesis of bacterial intestinal inflammation in marine fish and the efficient screening of preventive and therapeutic drugs.

Abstract:In order to comprehensively evaluate the application effects of in-situ and ex-situ biofloc technology for shrimp culture, growth performance, parameters of shrimp serum physiological, biochemical, and immunological of shrimp cultured in in-situ biofloc (IB) and ex-situ biofloc (EB) systems were investigated. A load of Vibrios in the water body and hepatopancreas of shrimp, concentrations of NH₄ ⁺ -N and NO₂ ^‒ -N in aquaculture water, as well as the bacterial community composition in flocs in IB and EB systems were monitored. The results indicated that the weight gain and specific growth rates of shrimp in group IB were significantly higher than those in group EB, feed conversion ratio in group IB was lower than that in group EB. Analysis of physiological and biochemical indicators showed that the activity of serum glutathione peroxidase (GSH-Px) in IB was significantly higher than that in EB (P＜0.05). Conversely, content of total cholesterol (T-CHO), total protein (TP), activities of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) showed no significant differences between group IB and EB(P＞0.05). Activity of phenoloxidase (PO) in shrimp of group IB was higher than that in EB (P＜0.05). However, the activities of peroxidase (POD), catalase (CAT), superoxide dismutase (SOD), and lysozyme (LZ) showed no significant differences between group IB and EB(P＞0.05). Vibrios load in water of group IB was significantly lower than that in group EB on days 30 and 50 (P＜0.05), However, the difference in Vibrios load in hepatopancreas of shrimp between group IB and EB was not statistically significant in all detection dates except on day 30 (P＞0.05). Concentration of NO₂ ^‒ -N and NH₄ ⁺ -N in group IB were significantly lower than those in group EB, respectively, at all sampling times (P＜0.05), except for no significant difference of NH₄ ⁺ -N between IB and EB on day 50. Moreover, the bacterial diversity of group IB was significantly higher than that of the EB. Taken together, in-situ bioflocs demonstrated superior performance over ex-situ bioflocs in promoting shrimp growth, improving water quality, and reducing Vibrio density. These findings could provide theoretical support for the wider application of biofloc technology in shrimp aquaculture systems.

Abstract:This study was conducted to explore the effects of different survival methods on the vital signs and quality indices of Crassostrea hongkongensis and to establish a prediction model. Three hundred oysters were divided into a control group (CK), purification group (PL), and ecological ice temperature dormancy group (PD). The experimental period was 9 days without water. The survival rate, microbial content, vital signs (heart rate, contraction rate, adductor muscle tension, mantle response time index) and nutritional quality (crude protein, glycogen, water, lactic acid, etc.) of each group were monitored every day. The results showed that the survival rate of the PD group was 96% after 9 days of survival, which was significantly higher than those of the CK group (61%) and PL group (70%). The mass loss rate of oysters in the PD group was 4.78%, which was significantly lower than those of the CK group (15.99%) and PL group (11.68%). The results showed that purification and ecological ice temperature dormancy treatment of C. hongkongensis significantly reduced mass loss during water-free survival, and ecological ice temperature dormancy and water-free survival treatment after temporary culture purification slowed microorganism growth. Among the vital signs evaluated, the decrease in heart rate (79.55%) and loss of adductor muscle tension were lower in the PD group than in the other groups, indicating alleviation of stress injury, an increase in the edge contraction rate, and slower mantle response time in the PD group. Among nutritional quality indicators, glycogen and fat consumption were significant. With the extension of the survival time of glycogen, the glycogen content in the CK group increased significantly more than that in the other two groups, and the change in the lactic acid content in each group increased with prolonged survival times. However, overall, the range of changes of quality indicators in the PD group was smaller than those in the other two groups. Additionally, quality reduction was lower in the PD groups than in the other groups, indicating that ecological ice temperature dormancy in the PD group slowed quality reductions by reducing the metabolic rate. Among the indicators of oxidative stress, the catalase activity in the CK group showed a fluctuating upward trend throughout the survival time and increased significantly at KA5d (survival time) (P＜0.05). The catalase activity of the PL and PD groups showed a gradually increasing trend, indicating that under dual stress, the body's oxidative stress was enhanced. Catalase, an antioxidant enzyme, responded to oxidative stress to clear the accumulated hydrogen peroxide in the body and protect cells from oxidative damage. Correlation analysis of the vital signs and quality indicators in the PD group showed that crude protein, glycogen, heart rate, edge contraction rate, adductor muscle tension, and mantle response time were strongly correlated. Based on the results, a multiple linear regression equation was established. The predictive regression equation was used to determine whether there was a collinearity problem between samples by the variance inflation factor value. Durbin-Watson statistics were used to evaluate the independence of samples, and R² was used to evaluate the fitting degree of the established model. Considering the above factors, a model with crude protein as the dependent variable was established: y = 8.298+0.003x₁–0.051x₂–0.046x₃–0.082x₄, where y is crude protein, x1 is the heart rate, x2 is the edge contraction rate, x₃ is muscle tension, and x₄ is the mantle response time, and R²=55.2%. The model with glycogen as the dependent variable was as follows: y=9.404–0.013x₁+0.829x₂+0.224x₃–1.945x₄, where y is glycogen, x₁ is the heart rate, x₂ is the shrinkage rate, x 3 is muscle tension, and X4 is the mantle response time, and R²=96.5%. These results showed that the independent variables of the two prediction models could explain the dependent variables. Using technology to keep oysters alive without water at ecological ice temperature may significantly prolong their survival time and maintain their quality. The model provides a theoretical basis for monitoring oyster activity in actual production.