Search Results (68)

Emaciation disease, primarily caused by the myxosporean parasite Enteromyxum leei, poses a significant economic threat to the olive flounder (Paralichthys olivaceus) aquaculture industry. Research on E. leei has been severely restricted by its status as an unculturable obligate parasite and its extreme sensitivity to cryopreservation. In this study, we developed a standardized in vitro culture system that achieved stable maintenance of E. leei for over 12 months for the first time. To overcome the challenges of primary isolation, a physical aggregation technique was implemented, which effectively concentrated the parasites while reducing bacterial contamination by 99.1%, as validated by qPCR. The established culture, maintained in minimum essential medium supplemented with 30% FBS at 25 °C, exhibited a consistent 20-day asexual proliferative cycle consisting of six distinct developmental stages. Morphological stability and genetic identity were rigorously monitored, showing no phenotypic drift or genetic divergence throughout the 12-month period. Our results demonstrate that the entire proliferative phase of E. leei can be recapitulated in vitro without host intervention. Given that cryopreservation remains non-viable, this continuous culture system provides a critical, unique platform for high-throughput drug screening and myxozoan developmental biology, offering a robust tool to mitigate emaciation syndrome in marine fish farms. Full article

While the impact of the environment on the fish microbiome remains under discussion, studies on the intestinal bacterial diversity of olive flounder are still limited. This study investigated the effects of three temperature conditions, 15 °C (Group L), 20 °C (Group M), and 25 °C (Group H), on the structure and diversity of the bacterial community in the gut of olive flounder. During the 35-day experiment, changes were observed in the composition and diversity of the gut microbiota, with alpha diversity estimates gradually decreasing as the temperature increased. At the species level, there were significant differences in the relative abundance of Sphingomonas echinoides and Photobacterium damselae between Groups L and H. According to LEfSe and correlation analyses, the relative abundances of Gammaproteobacteria, Alphaproteobacteria, Sphingomonas, and Photobacterium varied significantly depending on temperature levels. Through functional prediction, the predicted functional pathways based on bacterial abundances showed that those involved in aromatic compound degradation and amino acid metabolism were abundant in Group L, whereas pathogenic factors were abundant in Group H, suggesting a potential impact on host digestive and immune functions. These results suggest that temperature can significantly affect both the diversity and potential functional profiles of the intestinal microbiota in olive flounder. Full article

Oxytetracycline (OTC) is widely used in aquaculture to treat bacterial diseases, but its effects on drug metabolism and immune responses remain poorly understood in olive flounder (Paralichthys olivaceus). This study investigated the effects of OTC immersion for 1 h at different concentrations on the expression profile of drug metabolism- and immune-related genes and the histopathological changes in the gills and liver of olive flounder. The expression of Paralichthys olivaceus cytochrome P450 (PoCYP), Paralichthys olivaceus diphosphate (UDP)-glucuronosyltransferases (PoUGTs), and immune-related genes significantly increased at 12 and 24 h and then decreased at 72 h in the 100 and 200 ppm groups. By contrast, the 400 ppm group exhibited variable expression patterns depending on the gene and tissue. The highest expression levels were observed for PoIL-1β in the gills (22.7-fold) and PoCYP27B1 in the liver (58.0-fold) in the 400 ppm group. Histopathological analysis revealed macrophage activation in the liver at 72 h in the 200 ppm group, whereas epithelial edema and mild aneurysmal changes in the gills and macrophage activation in the liver were observed in the 400 ppm group. These findings provide insights into the effects of OTC exposure on drug metabolism and immune responses in olive flounder. Full article

Spermatogonial stem cells (SSCs) are pivotal in surrogate broodstock technology. However, species-specific protocols for the efficient enrichment and long-term preservation of SSCs in olive flounder (Paralichthys olivaceus) are not yet fully established. In this study, we evaluated and optimized methods for the isolation and cryopreservation of P. olivaceus SSCs. First, we compared two enrichment methods, including Percoll density gradient centrifugation (PDGC) and differential plating (DP). Although SSCs enriched by both methods showed increased expression of SSC-specific marker genes, PDGC resulted in significantly greater enrichment than DP. A combination of PDGC and DP did not further improve enrichment efficiency, suggesting that PDGC alone is sufficient in P. olivaceus. Second, we optimized cryopreservation conditions according to various cryoprotectants. Among the conditions, SSCs cryopreservation using 1.3 M propylene glycol (PG) as a permeating agent and 0.2 M raffinose (Raf) as a non-permeating cryoprotectant provided the highest cell viability (56.1%), demonstrating a synergistic protective effect. Finally, preliminary in vivo migration and localization ability of the cryopreserved SSCs was confirmed through xenotransplantation into zebrafish (Danio rerio) larvae. PKH26-labeled donor cells exhibited successful initial localization and short-term persistence within the presumptive gonadal ridge of the recipients at 5 days post-transplantation. These findings provide an optimized protocol for the handling and preservation of P. olivaceus germline resources, contributing to the technical advancement of surrogate reproduction strategies in this species. Full article

This study evaluated the effects of dietary host-derived Bacillus strains combined with fructo-oligosaccharide (FOS) on growth performance, basal physiological status, intestinal morphology, and thermal stress responses in juvenile olive flounder (Paralichthys olivaceus). A total of 486 fish with an initial body weight of 7.26 ± 0.04 g were randomly distributed into 27 tanks and fed nine experimental diets for nine weeks. The diets consisted of a basal control, an FOS-only diet, three single-strain synbiotic diets containing FOS and one host-derived Bacillus strain (B. sonorensis, B. subtilis, or B. velezensis), and four multi-strain synbiotic diets containing FOS and combinations of two or three strains. Probiotics were included at 1 × 10⁷ CFU g⁻¹ diet, and FOS was supplemented at 5 g kg⁻¹ diet. After the feeding trial, no significant dietary effects were observed on growth performance, somatic indices, whole-body proximate composition, plasma biochemical parameters, antioxidant enzyme activities, immune-related indicators, stress-related biomarkers, or intestinal morphology. Fish were subsequently subjected to lethal and acute high-temperature challenges to evaluate thermal stress tolerance and associated physiological responses. In the lethal temperature challenge, fish fed the multi-strain diets FOS + B. sonorensis + B. velezensis and FOS + B. sonorensis + B. subtilis + B. velezensis showed numerically higher survival than the other groups; however, these differences were not statistically significant. Following acute heat exposure, dietary treatments did not significantly affect plasma metabolites, and most heat-shock- and energy-metabolism-related genes were not differentially expressed among treatments. Hepatic AMPKβ expression showed a significant dietary treatment effect, with higher expression in the BCF and ACF groups than in the ABF group. Overall, host-derived synbiotic supplementation did not significantly enhance growth performance or basal physiological responses under the present experimental conditions. However, some multi-strain combinations showed a non-significant tendency toward higher survival under lethal thermal stress. Further studies incorporating gut microbiome profiling, metabolomic analysis, and alternative dietary conditions are required to clarify whether host-derived Bacillus–FOS synbiotic formulations can influence thermal stress resilience in olive flounder. Full article

The impacts of dietary xylooligosaccharide (XOS) were explored on growth, blood biochemistry, immune response, and resilience of olive flounder (Paralichthys olivaceus) against Edwardsiella tarda. Three replicate groups of fish (47.2 ± 0.41 g) were fed four diets incorporating various doses of XOS [0% (control), 1%, 2%, and 3%] to apparent satiety for eight weeks. Dietary inclusion of XOS improved growth performance and increased hepatosomatic and viscerosomatic indices. Serum alanine aminotransferase activity decreased with XOS supplementation, indicating improved liver status. Key innate immune parameters, including serum lysozyme, antiprotease, and alternative complement (ACH50) activities, were enhanced in XOS-fed fish. Skin mucus protein content also increased, whereas serum myeloperoxidase and glutathione peroxidase activities, as well as skin mucus antiprotease and protease activities, remained unchanged. XOS supplementation modulated serum bacteriostatic activity against non-pathogenic Escherichia coli and altered skin mucus lectin-binding patterns. Validation of the enhanced immune competence was confirmed by the enhancement of fish survival rate after exposure to E. tarda. Overall, the results demonstrate that dietary XOS, particularly at 3% inclusion, is effective in enhancing innate immunity and disease tolerance in olive flounder. Full article

In olive flounder (Paralichthys olivaceus) suffering from emaciation disease, the intestinal myxozoan Enteromyxum leei is considered a major causative agent. This disease causes severe economic losses in East Asian aquaculture, and even though the pathological outcomes have been well described, the molecular mechanisms underlying host immune imbalance are unclear. We performed RNA sequencing of posterior intestinal tissue from infected and control fish, yielding high-quality datasets and 2666 differentially expressed genes (1589 downregulated, 1077 upregulated). Enrichment analyses revealed a significant modulation of immune processes, particularly cytokine activity, chemokine signaling, apoptosis regulation, and lymphocyte trafficking. Kyoto Encyclopedia of Genes and Genomes analysis identified six immune-related pathways that were the most affected: Toll-like receptor, NOD-like receptor, intestinal immune network for IgA production, C-type lectin receptor, RIG-I-like receptor, and cytosolic DNA sensing. Network mapping highlighted nine hub genes, including cxcl8a, pik3r1, mapk10, and itpr1b, which were shared across multiple pathways and validated by qRT-PCR. Our results demonstrate that E. leei disrupts intestinal immune homeostasis by suppressing chemokine-driven inflammation and adaptive responses while simultaneously enhancing nucleic acid-sensing and stress pathways. This dual modulation provides new insights into the intestinal immune dysregulation underlying enteromyxosis and establishes a molecular basis for future diagnostic and preventive strategies in olive flounder aquaculture. Full article

This study aims to examine the factors influencing the acceptance of extruded pellet (EP) usage among Korea’s olive flounder farming households by analyzing their acceptance factors to provide recommendations for its wider adoption. A survey was conducted among olive flounder farming households, and 188 valid questionnaires were collected. To examine the factors influencing EP acceptance intention, the UTAUT2 (extended unified theory of acceptance and use of technology) model was used. The independent variables were categorized into performance expectancy, effort expectancy, facilitating conditions, social influence, price value, and reliability as independent variables, while acceptance intention was considered as the dependent variable, to derive measurement items. In addition, the differences between the two groups were analyzed by using the aquaculture region and the manager’s experience as moderating variables. The hypothesis testing showed that performance expectancy, effort expectancy, social influence, price value, and reliability factors had a positive effect on acceptance intention, while facilitating conditions did not show a significant effect. The analysis of the moderating effect of the aquaculture region indicated a significant difference between the Jeju-do and Jeollanam-do groups. Conversely, the moderating effect of experience showed no significant difference between those with more experience (≥10 years) and those with less (<10 years). Full article

Flumequine is an antibiotic that is used to treat bacterial diseases in aquaculture. Fish express drug-metabolizing genes in response to antibiotic exposure. However, studies on the effects of high flumequine concentrations on drug metabolism genes and histopathology of the olive flounder are limited. To investigate the response of olive flounder to flumequine, we administered it at different concentrations. We analyzed the expression of drug metabolism genes (CYP) in the liver and histopathological lesions in the liver, spleen, and kidneys. The gene expression levels of CYP were higher at the highest flumequine concentration tested (4×) than at the lowest flumequine concentration (1×). The highest CYP gene expression level was observed for CYP2B4 (46.6-fold) at 4× flumequine compared to that in the control group. Hepatic atrophy, lymphocytic infiltration, and hematopoiesis were observed in the liver, spleen, and kidney at 4× flumequine between 3 and 24 h compared to 1× flumequine, respectively. These results contribute to a better understanding of drug metabolism and the general toxicity of pharmaceutical exposure in olive flounder. Full article

The olive flounder (Paralichthys olivaceus) is a significant aquaculture species in Korea, yet production has stagnated due to rising costs, environmental pressures, and shifting consumer preferences. Enhancing farm efficiency is critical not only for economic viability but also for environmental sustainability, as efficient production reduces resource waste, lowers feed inputs, and minimizes the carbon output of aquaculture operations. This study estimated the production function and efficiency of olive flounder farms in Korea using stochastic frontier analysis, drawing on survey data collected directly from producers. Results indicate that the Cobb–Douglas model is more suitable than the translog model for empirical analysis. The average farm efficiency was 0.38, with the lowest recorded efficiency at 0.13. Key determinants of production efficiency included fry quality, workforce size, and feed management. Regional differences were also observed in the technical inefficiency factor. By identifying inefficiencies and management gaps, this study highlights opportunities to enhance resource use efficiency, reduce environmental and economic waste, and promote more sustainable practices. The findings provide insights for policymakers and farm managers seeking to strengthen both the profitability and sustainability of the Korean olive flounder aquaculture industry. Full article

A limited supply and price shortages of fishmeal with the expansion of aquaculture make it necessary to seek alternative protein sources. Soybean meal (SM) has been the widely preferred replacer for fishmeal in fish diets. Nevertheless, this substitution, especially when given at high doses, potentially shows adverse impact on fish intestinal health. This study aimed to investigate the effect of replacing fishmeal with SM on intestinal health in olive flounder (Paralichthys olivaceus). A 56-day feeding trial was conducted with 450 juvenile fish (initial weight: 6.32 ± 0.01 g) randomly allocated to five diets with graded SM replacement: 0% (FM), 12% (SM12), 24% (SM24), 36% (SM36), and 48% (SM48). The results demonstrated that concentrations of glucose, total triglyceride, and low-density lipoprotein cholesterol increased, whereas total protein and high-density lipoprotein cholesterol contents, and lysozyme activity decreased in serum with increasing dietary SM levels. Meanwhile, total antioxidant capacity and superoxide dismutase activity significantly decreased at replacement levels exceeding 24%, accompanied by elevated malondialdehyde concentration (p < 0.05). Compared with the FM group, the SM24, SM36, and SM48 groups showed significantly reduced VH and increased lamina propria width (p < 0.05). Increasing dietary SM levels upregulated expression of genes related to endoplasmic reticulum stress (ERS) (chop, perk, and grp78), inflammation (tnf-α and il-6), and apoptosis (bax, casp3, casp6, and casp9), while downregulated anti-inflammatory cytokines (il-10 and tgf-β1) and tight junction-related genes (zo-1, zo-2, claudin-5, ocln, muc-13, and muc-15) in the intestine (p < 0.05). There were significant differences in the abundances of intestinal microbiota at both the phylum and genus levels among the FM, SM24, and SM36 groups (p < 0.05), but the clusters and microbiota composition of the SM24 group were more similar to those of the FM group. In conclusion, replacing 24% of fishmeal with SM induced intestinal dysfunction through evoking ERS, inflammation, barrier disruption, and microbial dysbiosis in olive flounder. Full article

Olive flounder (Paralichthys olivaceus), a key aquaculture species in East Asia, is prone to stress and bacterial diseases under intensive farming. Antibiotics are often used to control these problems, but their overuse promotes resistance and threatens sustainability. To provide safer alternatives, this study evaluated the strain-specific effects of dietary probiotics on growth, immunity, and disease resistance in olive flounder. A five-week feeding trial was conducted to evaluate the effects of three isolates—Bacillus subtilis, Enterococcus faecium, and Pediococcus pentosaceus—on growth, blood biochemistry, immune responses, and resistance against Edwardsiella tarda. Each strain was incorporated individually into a basal diet. After the feeding trial, probiotic supplementation improved growth performance. P. pentosaceus significantly increased final body weight and other growth indices (p < 0.05), while E. faecium yielded the lowest feed conversion ratio. Plasma glucose was markedly reduced in the E. faecium and P. pentosaceus groups (p < 0.001), whereas other biochemical indices remained stable. Phagocytic activity was significantly increased in the B. subtilis (p < 0.05) and P. pentosaceus (p < 0.01) groups, while lysozyme activity was significantly elevated in the E. faecium (p < 0.01) and P. pentosaceus (p < 0.05) groups. Following the E. tarda challenge, survival improved in all probiotic-fed groups (22.5–28.9%) compared with the control (11.5%). These findings demonstrate complementary, strain-specific benefits: P. pentosaceus enhanced growth, E. faecium improved feed efficiency and disease resistance, and B. subtilis stimulated immune responses. Validation under farm conditions and exploration of multi-strain formulations are warranted to optimize probiotic use in olive flounder aquaculture. Full article

Feeding is among the most labor-intensive tasks in aquaculture, yet it is critical for productivity and operational efficiency. Although automated feeding systems reduce labor, the absence of data on optimal pellet size, feeding rate, and frequency has led to inconsistent practices and productivity. We evaluated the applicability of a low-cost automatic feeder and determined optimal pellet size and feeding frequency for juvenile olive flounder (Paralichthys olivaceus) in an experiment where 600 fish (83.4 ± 0.7 g (mean ± SD)) were randomly assigned to 12 flow-through tanks (60 fish/tank) in triplicate. In Experiment 1, fish fed 5-mm pellets presented greater weight gain and protein efficiency ratio (PER) than those fed 3-mm pellets (p < 0.05). In Experiment 2, manual feeding was compared to automatic feeding. Fish fed three times per day at a 1.3% daily feed intake (DFI) achieved similar growth but an improved feed conversion ratio and PER compared to manually fed fish (p < 0.05). Our findings support the use of 5-mm pellets at 1.3% DFI with a low-cost automatic feeder for maintaining productive juvenile flounder. These results present a practical automation strategy that enables small and medium-sized aqua-farms to reduce labor while maintaining productivity equivalent to manual feeding. Full article

Olive flounder (Paralichthys olivaceus) is a key aquaculture species in South Korea, but its production has been challenged by rising mortality under environmental stress from key environmental factors such as water temperature, dissolved oxygen, and feeding conditions. To support adaptive management, this study proposes a Bayesian Deep Kernel Machine Regression (BDKMR) model that integrates Gaussian process regression with neural network-based feature learning. Using longitudinal data from commercial farms, we model fish growth as a function of water temperature, dissolved oxygen, and feed quantity. Model performance is assessed via Leave-One-Out Cross-Validation and compared against kernel ridge regression and Bayesian kernel machine regression. Results show that BDKMR achieves substantially lower prediction errors, indicating superior accuracy and robustness. These findings suggest that BDKMR offers a flexible and effective framework for predictive modeling in aquaculture systems. Full article

This study aimed to investigate the prevalence, antimicrobial resistance (AMR), and virulence characteristics of Vibrio parahaemolyticus (V. parahaemolyticus) isolated from olive flounder (Paralichthys olivaceus) and rockfish (Sebastes schlegelii) sashimi samples sold in South Korea from 2021 to 2022. A total of 500 fish samples were analyzed, from which 17 V. parahaemolyticus isolates were obtained. Antibiotic susceptibility testing using the minimum inhibitory concentration method revealed that 58.8% (10/17) of the isolates exhibited resistance to ampicillin, indicating the potential for AMR transmission in seafood-associated pathogens. Whole-genome sequencing (WGS) and a polymerase chain reaction detected the presence of tlh and trh virulence genes in all isolates, suggesting their pathogenic potential. Although the overall isolation rate of V. parahaemolyticus was low, the presence of virulence and AMR genes indicates public health relevance associated with raw seafood consumption. The increasing consumer demand for raw fish, coupled with environmental changes such as rising ocean temperatures, underscores the necessity of continuous surveillance to prevent foodborne outbreaks. These findings emphasize the need for targeted AMR monitoring and further research to mitigate the dissemination of resistant V. parahaemolyticus strains and enhance seafood safety. Full article