Search Results (46)

Black rockfish (Sebastes schlegelii) is a marine ovoviviparous teleost that exhibits significant sexual dimorphism, with females growing faster and reaching larger sizes than males. Establishing stable oogonial stem cells (OSCs) is critical for understanding germline stem cell dynamics and facilitating all-female breeding. In this study, we successfully isolated and cultured OSCs from S. schlegelii for 12 passages. These cells exhibited alkaline phosphatase activity, expressed germline marker genes (ddx4, cdh1, klf4), and maintained a diploid karyotype (2n = 48). Transcriptomic comparisons between early (P3) and late (P12) passages revealed significant metabolic dysfunction and cell cycle arrest in the late-passage cells. Specifically, the down-regulation of glutathione-related and glycolysis-related genes (gstm3, gstt1, mgst3, gsta1, gsta4, gsto1, gapdh) and key mitotic regulators (cdk1, chk1, cdk4, e2f3, ccne2, ccnb1) suggested that metabolic imbalance contributes to oxidative stress, resulting in cell cycle inhibition and eventual senescence. This study provides a marine fish model for investigating metabolism-cell cycle interactions in germline stem cells and lays the foundation for future applications in germ cell transplantation and all-female breeding. 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

This study evaluated the antibacterial activity and residual functional compounds of blood orange (Citrus sinensis L. Osbeck) juice by-product extract (BJBE). The effects of dietary BJBE on growth performance, digestive enzyme activity, antioxidant status, immune parameters, and disease resistance against Vibrio harveyi were examined in juvenile black rockfish (Sebastes schlegelii). In total, 630 juvenile rockfish were randomly assigned to 21 rectangular tanks (50 L) for a feeding trial, with 30 fish per tank in triplicate. Seven isonitrogenous and isolipidic experimental diets were formulated with BJBE at 0 (control, BJBE0), 0.1 (BJBE0.1), 0.2 (BJBE0.2), 0.3 (BJBE0.3), 0.5 (BJBE0.5), 0.7 (BJBE0.7), and 1.0 (BJBE1) g kg⁻¹. A disk diffusion assay confirmed BJBE’s strong antibacterial efficacy against V. harveyi. After an 8-week feeding trial, fish fed BJBE0.7 and BJBE1 exhibited significantly a greater final weight, weight gain, and specific growth rate compared with those fed BJBE0. Feed efficiency was significantly higher in fish fed BJBE0.7 than in those fed BJBE0. The protein efficiency ratio was significantly higher in fish fed BJBE0.3, BJBE0.5, BJBE0.7, and BJBE1 relative to those fed BJBE0. Intestinal amylase activity was significantly higher in fish fed BJBE0.7 and BJBE1 compared with those fed BJBE0, and trypsin activity was significantly higher in BJBE0.7-fed fish than in BJBE0-fed fish. In comparison to the BJBE0 diet, the plasma superoxide dismutase, catalase, and glutathione levels of fish fed BJBE0.7 and BJBE1 diets were significantly higher. Lysozyme activity and immunoglobulin M level in fish fed BJBE0.7 and BJBE1 were significantly higher than that in fish fed BJBE0. After a challenge with V. harveyi, disease resistance was significantly higher in fish fed BJBE0.5, BJBE0.7, and BJBE1 compared with those fed BJBE0. Overall, 0.7–1.0 g kg⁻¹ is proposed as the optimal dietary BJBE inclusion level for enhancing growth performance, digestive enzyme activity, antioxidant status, immune parameters, and disease resistance against V. harveyi infection in juvenile black rockfish. Full article

This study examined the effects of stress and social enrichment on fish neuroplasticity and antioxidant capacity, addressing growing concerns about fish welfare in aquaculture. A 2 × 2 × 2 factorial design comprising eight treatment groups was implemented to investigate how bait type, group size (two distinct sizes tested), and stress level affected the expression of neurogenesis-related genes (PCNA, DCX, and NeuroD) and antioxidant parameters (MDA levels, CAT, GSH-Px, and SOD activity) in the fish. The findings demonstrated that social enrichment significantly reduced aggressive behavior and basal cortisol levels and enhanced the expression of neurogenesis-related gene. However, the optimal group-size augmentation (between the two group sizes tested) considerably increased the activity of antioxidant enzymes and decreased MDA levels. Acute stress further upregulated cortisol levels and the expression of genes related to neurogenesis. A scientific foundation for enhancing fish welfare in aquaculture is provided by the study’s confirmation that social enrichment reduces stress and fosters neuroplasticity. Full article

Aggressive behavior is regulated by intricate neural circuits and molecular mechanisms, notably through the interaction of brain-derived neurotrophic factor (BDNF) with its receptor, tropomyosin receptor kinase B (TrkB), which influences neuroplasticity and related behavioral phenotypes. We investigate the role of the BDNF signaling pathway in fish aggression using juvenile black rockfish (Sebastes schlegelii), which exhibit distinct aggressive phenotypes. The TrkB agonist 7,8-dihydroxyflavone (7,8-DHF) was administered intraperitoneally at doses of 1.25, 2.5, and 5 mg/kg to assess its effects on the behavioral characteristics of high-aggression (H-agg) and low-aggression (L-agg) phenotypes. Our findings indicate the following: (1) The effects of 7,8-DHF are dose-dependent, with 2.5 mg/kg identified as the effective threshold dose for H-agg individuals; (2) in the H-agg group, this dose significantly reduced locomotor acceleration, angular velocity, and activity frequency, while prolonging the first movement latency; (3) in the L-agg group, only angular velocity was significantly decreased with the 2.5 mg/kg treatment, with no significant changes observed in other behavioral parameters. This study provides the first evidence for differential behavioral responses to 7,8-DHF in S. schlegelii, demonstrating dose-dependent aggression suppression in H-agg phenotypes and threshold-specific responses in L-agg phenotypes. These insights into the neuro-molecular basis of fish aggression can guide phenotype-specific management in aquaculture, potentially improving stress management, reducing injuries and mortality, and boosting productivity. Full article

As a lysosomal cysteine protease of the papain subfamily, cathepsin B (CTSB) is characterized by its innate immune functions and hydrolytic activity. However, the functions of CTSB in the immune responses of teleosts remain to be clarified. In this study, two CTSB genes in S. schlegelii, SsCTSBa and SsCTSBb, were identified. Both SsCTSBa and SsCTSBb are composed of a 993 bp ORF encoding 330 amino acids. It was found in a phylogeny analysis that both genes form monophyletic clades with their orthologous counterparts of Honeycomb rockfish (Sebastes umbrosus). A synteny analysis indicated that the CTSB homologues were comparatively conserved during vertebrate evolution. Additionally, quantitative real-time PCR revealed the ubiquitous mRNA expression of SsCTSBa and SsCTSBb in all of the examined tissues, and substantially differential expression patterns could be observed following Aeromonas salmonicida infection. A subcellular localization analysis demonstrated that the distribution of SsCTSBa and SsCTSBb was mainly in the cytoplasm. Moreover, rSsCTSBa and rSsCTSBb showed strong binding to Poly(I:C) and exhibited diverse agglutination effects on different bacteria. Overall, these findings suggest that the CTSB genes in black rockfish might show essential functions in the host defense of teleosts against bacterial infections, providing valuable insights for further investigations into the immune mechanism of teleost CTSB. Full article

Background: Amoxicillin (AMOX) is widely used in aquaculture for bacterial infections due to its efficacy and safety. Despite official approval for select species, off-label use is common. This study evaluated the antibacterial efficacy and residue depletion of AMOX in five aquaculture species: olive flounder (Paralichthys olivaceus), rainbow trout (Oncorhynchus mykiss), Japanese eel (Anguilla japonica), black rockfish (Sebastes schlegelii), and Israeli carp (Cyprinus carpio). Methods: Fish were administered AMOX orally at 40 mg/kg and 80 mg/kg for seven days. Antibacterial efficacy was assessed by bacterial load reduction and survival rates following artificial infection. Residue depletion was analyzed using HPLC–MS/MS to determine the time required for AMOX levels to fall below the maximum residue limit (MRL, 0.05 mg/kg). Results: AMOX, at 40 mg/kg, significantly reduced bacterial loads in olive flounder, rainbow trout, and Japanese eel (p < 0.05), while Israeli carp exhibited a limited response (p = 0.54). Black rockfish showed moderate efficacy (RPS 72.7%) but increased mortality at 80 mg/kg. Residue levels fell below the MRL within 10 days for all species except Israeli carp (~30 days). Conclusions: These findings highlight species-specific differences in AMOX efficacy and residue depletion rates, emphasizing the necessity of tailored dosing regimens and withdrawal periods to ensure optimal therapeutic outcomes and food safety compliance in aquaculture. Further pharmacokinetic studies are needed to refine dosing strategies, particularly for species with extended residue retention and potential dose-dependent adverse effects. Full article

Spermatogenesis, the process of male germ cell development, is tightly regulated by the hypothalamic–pituitary–testis (HPT) axis in seasonally breeding teleosts. Despite its importance, our understanding of how the brain and male germ cells coordinate key transitions—such as testis initiation and maturation—remains limited, particularly in species with distinct seasonal reproductive cycles. Black rockfish (Sebastes schlegelii), a marine viviparous teleost, exhibits a prolonged testis quiescent phase lasting three-quarters of the year, with testis initiation occurring in September and maturation concluding in November and December. The mechanisms underlying these transitions are poorly characterized, leaving a critical gap in our knowledge of seasonal spermatogenesis and its regulation. Addressing this gap is crucial for advancing artificial breeding technologies, which could significantly benefit the aquaculture industry. RNA-seq was used to explore the gene regulatory networks involved in testis initiation in S. schlegelii. Transcriptomic analyses of brain and testis were conducted across key developmental phases. In the brain, upregulated genes were notably involved in neuroactive ligand–receptor interactions, whereas in the testis, differentially expressed genes were linked to cell cycle processes and ATP-dependent chromatin remodeling. Our findings reveal the molecular mechanisms underlying testis initiation in S. schlegelii, providing omics evidence for the role of the HPT axis in regulating this process. By elucidating the gene regulatory networks of the brain and testis during critical transitions, this study advances our understanding of spermatogenesis in seasonally breeding teleosts. These insights pave the way for developing year-round artificial breeding technologies, contributing to the sustainable management of commercially valuable fish species. Full article

Photobacterium damselae subsp. Piscicida (PDP), a marine bacterium, has been reported to infect a variety of economically important marine species worldwide. Understanding the occurrence and pathogenicity of PDP is crucial for effective disease control and ensuring the success of aquaculture operations. In late August 2023, an epidemic outbreak of P. damselae subsp. piscicida DQ-SS1, accompanied by significant mortality, was recorded in cage-cultured black rockfish (Sebastes schlegelii) located on Daqin Island for the first time. Genomic analysis revealed that DQ-SS1 possesses 2 chromosomes, with a total size of 4,510,445 bp and 3923 predicted CDSs. Pathogenic genes analysis identified 573 and 314 genes related to pathogen–host interactions and virulence, respectively. Additionally, DQ-SS1 displayed susceptibility to 15 antimicrobials, was resistant to 11 antimicrobials, and was intermediately sensitive to four antibiotics. Meanwhile, the in vitro assay revealed that the extracellular products (ECP) of DQ-SS1 were lethal to macrophages and exhibited hemolysin, lipase, and amylase activities. Moreover, DQ-SS1 also demonstrated the ability to survive in fish serum and resist complement-mediated killing. The in vivo assay showed that the infected fish exhibited severe histopathological alterations, such as the infiltration of inflammatory cells, cellular degeneration and necrosis, and loose cell aggregation. Lastly, the in vivo infection assays revealed the LD₅₀ of DQ-SS1 was 1.7 × 10³ CFU/g. This is the first study to elucidate the pathogenicity and genomic characteristics of multidrug-resistant PDP in cage-cultured S. schlegelii, which contributes to the advancement of diagnostic and preventative strategies for this disease in marine-cultured fishes and provides information for an in-depth study of the pathogenic mechanism of PDP. Full article

The current experiment is conducted to determine the effects of chicken by-product meal (CBM) as a fish meal (FM) replacer in diets, with or without the inclusion of jack mackerel (Trachurus japonicus) meal (JMM), on the growth and feed availability of rockfish (Sebastes schlegeli). A two-way ANOVA experimental design [FM replacement level (FMRL, 25% and 50%) × JMM inclusion (without and with)] was adopted. The control (Con) diet contained 55% FM. In the Con diet, 25% and 50% of FM were substituted with CBM, either without or with the inclusion of 22% JMM, referred to as the CBM25, CBM50, CBM25J, and CBM50J diets, respectively. A total of 375 juvenile fish were distributed into 15 tanks with triplicates. The 25% FM replacement diets led to significantly (p < 0.003 and p < 0.004, respectively) greater weight gain and specific growth rate (SGR) of rockfish than the 50% FM replacement diets. Furthermore, the CBM-replaced diets with JMM inclusion led to significantly (p < 0.003 and p < 0.002, respectively) greater weight gain and SGR of fish compared with those without JMM inclusion. Weight gain and SGR of rockfish fed the Con and CBM25J diets were significantly (p < 0.001 for both) greater than those of fish fed the CBM25, CBM50, and CBM50J diets. However, neither dietary FMRL nor JMM inclusion had significant (p > 0.05) effects on feed consumption, blood chemistry, or the biochemical composition of rockfish. In conclusion, 25% of FM could be replaced with CBM in the 55% FM-based diet, including JMM, without adverse effects on the growth, feed availability, blood chemistry, or biochemical composition (proximate composition and amino and fatty acid profiles) of rockfish. Full article

A 56-day feeding experiment was carried out to evaluate the effects of substituting fish meal (FM) with chicken by-product meal (CBM) in diets on the growth and feed utilization of rockfish (Sebastes schlegeli). Six experimental diets were formulated to be isonitrogenous and isolipidic. The control (Con) diet included 55% FM. In the Con diet, 10%, 20%, 30%, 40%, and 50% of FM was replaced with CBM, named as the CBM₁₀, CBM₂₀, CBM₃₀, CBM₄₀, and CBM₅₀ diets, respectively. A total of 540 juvenile fish were distributed into 18 tanks (30 fish per tank and 3 tanks per diet) and fed to apparent satiation two times daily for 56 days. The weight gain and specific growth rate of rockfish fed the CBM₁₀ and CBM₂₀ diets were comparable to rockfish fed the Con diet. The feed consumption of rockfish fed the Con and CBM₁₀ diets was significantly (p < 0.001) higher than that of fish fed all other diets, except for the CBM₂₀ diet. However, protein retention, biometric indices, chemical composition, amino acid profiles, and plasma and serum parameters of rockfish were not significantly influenced by dietary FM substitution with CBM. The Con, CBM₁₀, and CBM₂₀ diets showed superior (p < 0.001) economic profit index (EPI) compared to the CBM₃₀, CBM₄₀, and CBM₅₀ diets. Conclusively, FM up to 20% could be substituted by CBM in diets without impairing growth, feed availability, chemical composition, amino acid profiles, and blood parameters of rockfish grown from 2.5 g to 12.5 g. However, the long-term effects of CBM substitution or the potential use of combined CBM and other alternative protein sources for FM in rockfish diets are needed in future. Full article

This study evaluated bioactive compounds in blood orange (Citrus sinensis (L.) Osbeck) peel (BOP) as dietary additives. An 8-week feeding trial was conducted to investigate the effects of dietary supplementation on the growth performance, body composition, digestive enzyme activity, antioxidant capacity, and immune response of juvenile black rockfish. A total of 1260 juvenile rockfish (1.4 ± 0.01 g) were randomly distributed into seven treatment groups, each with 50 fish per circular tank. The groups were fed seven different diets containing graded levels of 0 (control, BOP0), 1 (BOP1), 2 (BOP2), 3 (BOP3), 5 (BOP5), 7 (BOP7), and 10 (BOP10) g kg⁻¹, respectively. The BOP10 diet significantly enhanced the final weight, weight gain, specific growth rate, protein efficiency ratio, and protein retention in fish. The BOP treatments notably affected the fishes’ whole-body crude protein and lipid contents. Plasma total cholesterol levels of fish fed the BOP0 and BOP1 diets were significantly higher than those fed the BOP7 and BOP10 diets. The activities of trypsin and lipase were significantly affected by dietary BOP levels. The antioxidant enzyme activity in the plasma of fish fed the BOP10 diet was significantly higher than those fed the BOP0 diet. The lysozyme activity and levels of immunoglobulin M and G in fish fed the BOP0 diet were significantly lower than those in fish fed the BOP10 diet. In conclusion, dietary supplementation of BOP at 10 g kg⁻¹ improved the growth performance and overall health of juvenile black rockfish. Full article

Atopic dermatitis (AD) is a chronic inflammatory skin disorder associated with significant morbidity, including pruritus, recurrent skin lesions, and immune dysregulation. This study aimed to investigate the antioxidative and anti-AD effects of peptides derived from hydrolyzed Sebastes schlegelii (Korea rockfish) tail by-products. Hydrolysates were prepared using various enzymes, including Alcalase, Flavourzyme, Neutrase, and Protamex. Among them, Protamex hydrolysates demonstrated the highest ABTS radical scavenging activity with an RC₅₀ value of 69.69 ± 0.41 µg/mL. Peptides were further isolated from the Protamex hydrolysate using dialysis, fast protein liquid chromatography (FPLC), and high-performance liquid chromatography (HPLC). The most active peptide, STPO-B-II, exhibited a single peak and was identified as a sequence of Glu-Leu-Ala-Lys-Thr-Trp-His-Asp-Met-Lys, designated as MP003. In vivo experiments were conducted using a 2,4-dinitrochlorbenzene (DNCB)-induced AD model in NC/Nga mice. The isolated peptide, MP003, showed significantly reduced AD symptoms, including erythema, lichenification, and collagen deposition. Additionally, MP003 decreased epidermal and dermal thickness, eosinophil, and mast cell infiltration and downregulated the expression of pro-inflammatory cytokines IL-1β, IL-6, and IgE in serum and skin tissues. These findings suggest that peptides derived from Sebastes schlegelii tail by-products may serve as potential therapeutic agents for AD. Full article

The rockfish (Sebastes schlegeli) and striped beakperch (Oplegnathus fasciatus) were released in marine ranching areas in Korea, Japan, and China to maintain fishery resources in coastal areas. To estimate the density and biomass of fishery resources, the target strength (TS) of target marine organisms is needed to scale integrated volume backscattering coefficients. In this study, the target strength–length (TS–L) relationship for live rockfish and striped beakperch was derived using ex situ methods at a frequency of 200 kHz. The TS-L function for rockfish and striped beakperch can be expressed as TS_Avg. = 20logTL − 69.25 (R² = 0.35) and TS_Avg. = 20logFL − 67.01 (R² = 0.31), respectively. These results can be used to assess the growth, density, and abundance of the two species using acoustics. Full article

This study was designed to evaluate the effects of yacon (Smallanthus sonchifolius) juice byproduct (YJB) on the growth performance, digestive and antioxidant enzyme activities, and disease resistance against Streptococcus iniae of juvenile black rockfish (Sebastes schlegelii) based on different feeding schedules. Four different YJB feeding strategies were evaluated: feeding the fish a basal diet continuously (control, T0), feeding them YJB (2.5 g/kg) continuously (T1), feeding them YJB for 1 day and the basal diet the next day (T2), and feeding them YJB for 1 day and the basal diet for the following 2 days (T3). No difference in survival among the treatments was found after the 8-week feeding trial (p > 0.05). However, the T1 and T2 groups exhibited significant enhancements in final body weight, weight gain, and specific growth rate compared with the T0 and T3 groups. Furthermore, the T1 and T2 groups showed a significant improvement in feed consumption, feed efficiency, and protein efficiency ratio compared with the T0 and T3 groups. No significant differences in the condition factor or viscerosomatic and hepatosomatic indices were observed among all the groups. Intestinal amylase, trypsin, and lipase activity was significantly (p < 0.05) higher in the T1 and T2 groups than in the T0 and T3 groups. Lysozyme, superoxide dismutase, and catalase activity along with glutathione peroxidase content were significantly (p < 0.05) higher under all YJB feeding regimens than those under the control treatment. The survival rates in all the YJB treatment groups after the S. iniae challenge were significantly (p < 0.05) enhanced. In conclusion, we recommend offering YJB at day-to-day intervals to improve growth performance, digestive enzyme activity, antioxidant status, and disease resistance against S. iniae. Full article