Pub Date : 2026-10-30Epub Date: 2025-06-30DOI: 10.1016/j.aquaculture.2025.742912
Yanbiao Guo , Bin Jiang , Huixiang Chen , Haifu Zhang , Jingyin Liu , Jintao lǚ , Lingxiao Li , Wenxi Zhong , Shichao Wen , Chunlan Liang , Yi Huang , Zhiping Liang , Junpeng Cai
<div><div><em>Bdellovibrio</em> is a kind of fast-moving bacteria that mainly preys on Gram-negative bacteria. <em>Aeromonas hydrophila</em> is one of the most common pathogenic bacteria for many animals. However, the potential application of freshwater-derived <em>Bdellovibrio</em> in protecting eels from <em>A. hydrophila</em> infection is still unclear. In this study, <em>Klebsiella</em> was used as the host bacteria, and <em>Bdellovibrio</em>-and-like organisms (BALOs) were isolated by double-layer plate technique. 32 strains of pathogenic bacteria from different sources including: one Gram-positive pathogenic stain of <em>Bacillus cereus</em> and 31 Gram-negative pathogenic stains of <em>A. hydrophila, Escherichia coli</em>, <em>Pantoea agglomerans</em>, <em>Providencia rettgeri</em>, <em>Pseudomonas aeruginosa</em>, <em>Salmonella Choleraesuis</em>, <em>Salmonella Typhimurium</em>, <em>Serratia odorifera</em>, <em>Shewanella Putrefaciens</em>, <em>Vibrio parahaemolyticus</em>, to name just a few. Moreover, 5 strains of potential probiotics including <em>Bacillus coagulans</em>, <em>Lactobacillus plantarum</em>, and <em>Lactobacillus salivarius</em> were also used to select the <em>Bdellovibrio</em> strain with a relatively wide lysis spectrum and no adverse effects on potential probiotics. Transmission electron microscopy and BALO-specific polymerase chain reaction [PCR] techniques were employed to identify BALOs strains. The application of BALOs strains in controlling <em>A. hydrophila</em> infections of American eel (<em>Anguilla rostrata</em>) was also conducted. Results showed that 8 strains of BALOs, viz. FSBD1, FSBD2, FSBD3, FSBD4, FSBD5, FSBD6, ZZBD1 and ZZBD2 were isolated. Lysis experiments on 32 potentially pathogens showed that FSBD1, FSBD2 FSBD3, FSBD4, FSBD5, FSBD6, ZZBD1 and ZZBD2 lysed 65.6%6 % (21/32), 65.6% (21/32), 65.6 % (21/32), 65.6 %6 % (21/32), 87.5 % (28/32), 75.0 % (24/32), 84.4 % (27/32) and 71.9 % (23/32) pathogens, respectively. Among of them, FSBD5 had the highest lysis rate of 87.5 % (28/32). It showed great lysis ability to 100.0 % (4/4) <em>Salmonella</em> and 100.0 % (4/4) <em>Aeromonas</em> tested. However, its lysis rate of potential 5 probiotics strains was 0 % (0/5). Surprisingly, ZZBD1 lysed one Gram-positive pathogenic stain of <em>B. cereus</em>, with the Gram-positive lysis rate of 16.7 % (1/6). FSBD5 and ZZBD1 were identified as BALOs morphologically by transmission electron microscopy and partial <em>16S rDNA</em> sequencing. Concerning the strain of FSBD5, compared with <em>A. hydrophila</em> infection group (AHI), adding the cultured FSBD5 to the rearing water of American eel significantly reduced the number of <em>A. hydrophila</em> in <em>Bdellovibrio</em> treatment group (BDT, from 6.19 ± 0.01 log CFU/mL to 2.84 ± 0.08 log CFU/mL, <em>p</em> < 0.05), and also significantly improved the survival rate of American eel (at the end of 7 days experiment, the survival rate of AHI and BDT group was
{"title":"Isolation and application of Bdellovibrio and like organisms (BALOs) for controlling Aeromonas hydrophila in the American eel (Anguilla rostrata) rearing water","authors":"Yanbiao Guo , Bin Jiang , Huixiang Chen , Haifu Zhang , Jingyin Liu , Jintao lǚ , Lingxiao Li , Wenxi Zhong , Shichao Wen , Chunlan Liang , Yi Huang , Zhiping Liang , Junpeng Cai","doi":"10.1016/j.aquaculture.2025.742912","DOIUrl":"10.1016/j.aquaculture.2025.742912","url":null,"abstract":"<div><div><em>Bdellovibrio</em> is a kind of fast-moving bacteria that mainly preys on Gram-negative bacteria. <em>Aeromonas hydrophila</em> is one of the most common pathogenic bacteria for many animals. However, the potential application of freshwater-derived <em>Bdellovibrio</em> in protecting eels from <em>A. hydrophila</em> infection is still unclear. In this study, <em>Klebsiella</em> was used as the host bacteria, and <em>Bdellovibrio</em>-and-like organisms (BALOs) were isolated by double-layer plate technique. 32 strains of pathogenic bacteria from different sources including: one Gram-positive pathogenic stain of <em>Bacillus cereus</em> and 31 Gram-negative pathogenic stains of <em>A. hydrophila, Escherichia coli</em>, <em>Pantoea agglomerans</em>, <em>Providencia rettgeri</em>, <em>Pseudomonas aeruginosa</em>, <em>Salmonella Choleraesuis</em>, <em>Salmonella Typhimurium</em>, <em>Serratia odorifera</em>, <em>Shewanella Putrefaciens</em>, <em>Vibrio parahaemolyticus</em>, to name just a few. Moreover, 5 strains of potential probiotics including <em>Bacillus coagulans</em>, <em>Lactobacillus plantarum</em>, and <em>Lactobacillus salivarius</em> were also used to select the <em>Bdellovibrio</em> strain with a relatively wide lysis spectrum and no adverse effects on potential probiotics. Transmission electron microscopy and BALO-specific polymerase chain reaction [PCR] techniques were employed to identify BALOs strains. The application of BALOs strains in controlling <em>A. hydrophila</em> infections of American eel (<em>Anguilla rostrata</em>) was also conducted. Results showed that 8 strains of BALOs, viz. FSBD1, FSBD2, FSBD3, FSBD4, FSBD5, FSBD6, ZZBD1 and ZZBD2 were isolated. Lysis experiments on 32 potentially pathogens showed that FSBD1, FSBD2 FSBD3, FSBD4, FSBD5, FSBD6, ZZBD1 and ZZBD2 lysed 65.6%6 % (21/32), 65.6% (21/32), 65.6 % (21/32), 65.6 %6 % (21/32), 87.5 % (28/32), 75.0 % (24/32), 84.4 % (27/32) and 71.9 % (23/32) pathogens, respectively. Among of them, FSBD5 had the highest lysis rate of 87.5 % (28/32). It showed great lysis ability to 100.0 % (4/4) <em>Salmonella</em> and 100.0 % (4/4) <em>Aeromonas</em> tested. However, its lysis rate of potential 5 probiotics strains was 0 % (0/5). Surprisingly, ZZBD1 lysed one Gram-positive pathogenic stain of <em>B. cereus</em>, with the Gram-positive lysis rate of 16.7 % (1/6). FSBD5 and ZZBD1 were identified as BALOs morphologically by transmission electron microscopy and partial <em>16S rDNA</em> sequencing. Concerning the strain of FSBD5, compared with <em>A. hydrophila</em> infection group (AHI), adding the cultured FSBD5 to the rearing water of American eel significantly reduced the number of <em>A. hydrophila</em> in <em>Bdellovibrio</em> treatment group (BDT, from 6.19 ± 0.01 log CFU/mL to 2.84 ± 0.08 log CFU/mL, <em>p</em> < 0.05), and also significantly improved the survival rate of American eel (at the end of 7 days experiment, the survival rate of AHI and BDT group was","PeriodicalId":8375,"journal":{"name":"Aquaculture","volume":"610 ","pages":"Article 742912"},"PeriodicalIF":3.9,"publicationDate":"2026-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144572279","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"农林科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-10-30Epub Date: 2025-07-06DOI: 10.1016/j.aquaculture.2025.742933
Meiqian Pang , Haigang Qi , Chaogang Wang , Rihao Cong , Mingyang Du , Zhuxiang Jiang , Min Wang , Li Li , Guofan Zhang
Oysters are characterized by an extremely high taurine content, a feature that constitutes one of the key reasons for the nutritional and commercial value of these shellfish. Nevertheless, within these organisms, the functions of key metabolic genes and their regulatory mechanisms remain poorly understood. In the current study, we confirmed that cysteine sulfinic acid decarboxylase (CSAD) catalyzes taurine synthesis in two congeneric oyster species: the Pacific oyster Crassostrea gigas and the Portuguese oyster Crassostrea angulata. These oysters are notable for their high aquaculture yields and distinct thermal tolerance levels. Csad displayed distinct thermal response patterns in the two oyster species and significantly contributed to the enhancement of thermal tolerance. Three genomic variations in the Csad promoter region were identified. These variations enhanced the transcriptional activity by varying degrees under heat stress conditions, with the activity increasing from 2.52-fold to 3.19-fold, 2.81-fold and 4.30-fold respectively. Our findings establish Poly (ADP-ribose) polymerase 1 (PARP1) as a transcriptional coregulator mediating the species-divergent thermal response of Csad. This research fills a significant void in our understanding of the regulatory mechanisms of taurine metabolism in marine invertebrates and has the potential to lay a theoretical groundwork for the genetic improvement of oysters via molecular-based methodologies.
{"title":"Functional characterization of CSAD and its genomic variations modulating taurine synthesis and heat adaptation between two congeneric oyster species","authors":"Meiqian Pang , Haigang Qi , Chaogang Wang , Rihao Cong , Mingyang Du , Zhuxiang Jiang , Min Wang , Li Li , Guofan Zhang","doi":"10.1016/j.aquaculture.2025.742933","DOIUrl":"10.1016/j.aquaculture.2025.742933","url":null,"abstract":"<div><div>Oysters are characterized by an extremely high taurine content, a feature that constitutes one of the key reasons for the nutritional and commercial value of these shellfish. Nevertheless, within these organisms, the functions of key metabolic genes and their regulatory mechanisms remain poorly understood. In the current study, we confirmed that cysteine sulfinic acid decarboxylase (CSAD) catalyzes taurine synthesis in two congeneric oyster species: the Pacific oyster <em>Crassostrea gigas</em> and the Portuguese oyster <em>Crassostrea angulata</em>. These oysters are notable for their high aquaculture yields and distinct thermal tolerance levels. <em>Csad</em> displayed distinct thermal response patterns in the two oyster species and significantly contributed to the enhancement of thermal tolerance. Three genomic variations in the <em>Csad</em> promoter region were identified. These variations enhanced the transcriptional activity by varying degrees under heat stress conditions, with the activity increasing from 2.52-fold to 3.19-fold, 2.81-fold and 4.30-fold respectively. Our findings establish Poly (ADP-ribose) polymerase 1 (PARP1) as a transcriptional coregulator mediating the species-divergent thermal response of <em>Csad</em>. This research fills a significant void in our understanding of the regulatory mechanisms of taurine metabolism in marine invertebrates and has the potential to lay a theoretical groundwork for the genetic improvement of oysters via molecular-based methodologies.</div></div>","PeriodicalId":8375,"journal":{"name":"Aquaculture","volume":"610 ","pages":"Article 742933"},"PeriodicalIF":3.9,"publicationDate":"2026-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144605998","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"农林科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-10-30Epub Date: 2025-07-06DOI: 10.1016/j.aquaculture.2025.742931
Inyeong Kwon , Ju-Ae Hwang
This study sought to evaluate the physiological stress responses of olive flounder (Paralichthys olivaceus) to varying stocking densities by analyzing heart rate and heart rate variability (HRV). All experiments were conducted in flow-through tanks under both normal- and high-density conditions. Bio-loggers were implanted in the fish to continuously monitor their heart rates and HRV over a 25-day period. The collected data were processed using the Mercury software, using only high-quality heart rate data. To evaluate HRV, the coefficient of variation (CV) was calculated, offering a standardized measure of heart rate variability. The fish in the high-density environments exhibited significantly higher heart rates and lower HRVs than those in normal-density environments. Elevated plasma cortisol levels in the high-density group (p < 0.05) further validated the stress responses indicated by heart rate and HRV. These findings suggest that high-density conditions induce significant stress in olive flounder, potentially reducing physiological adaptability and autonomic nervous system balance due to sympathetic dominance. This underscores the importance of density management in aquaculture to enhance fish welfare and highlights HRV analysis as a reliable, non-invasive tool for stress assessment.
{"title":"Heart rate variability as a neurophysiological biomarker of stress and welfare in olive flounder (Paralichthys olivaceus) under varying stocking densities","authors":"Inyeong Kwon , Ju-Ae Hwang","doi":"10.1016/j.aquaculture.2025.742931","DOIUrl":"10.1016/j.aquaculture.2025.742931","url":null,"abstract":"<div><div>This study sought to evaluate the physiological stress responses of olive flounder (<em>Paralichthys olivaceus</em>) to varying stocking densities by analyzing heart rate and heart rate variability (HRV). All experiments were conducted in flow-through tanks under both normal- and high-density conditions. Bio-loggers were implanted in the fish to continuously monitor their heart rates and HRV over a 25-day period. The collected data were processed using the Mercury software, using only high-quality heart rate data. To evaluate HRV, the coefficient of variation (CV) was calculated, offering a standardized measure of heart rate variability. The fish in the high-density environments exhibited significantly higher heart rates and lower HRVs than those in normal-density environments. Elevated plasma cortisol levels in the high-density group (<em>p</em> < 0.05) further validated the stress responses indicated by heart rate and HRV. These findings suggest that high-density conditions induce significant stress in olive flounder, potentially reducing physiological adaptability and autonomic nervous system balance due to sympathetic dominance. This underscores the importance of density management in aquaculture to enhance fish welfare and highlights HRV analysis as a reliable, non-invasive tool for stress assessment.</div></div>","PeriodicalId":8375,"journal":{"name":"Aquaculture","volume":"610 ","pages":"Article 742931"},"PeriodicalIF":3.9,"publicationDate":"2026-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144579909","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"农林科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-10-30Epub Date: 2025-07-01DOI: 10.1016/j.aquaculture.2025.742917
Alexis Viel , Florine Bachelet , Annaëlle Chailleux , Céline David , Lionel Pineau , Ségolène Calvez , Antoine Rostang
The aim of this study was to perform a pharmacokinetic (PK) study of oxytetracycline (OTC) in rainbow trout using different routes of administration and different doses, and to investigate the influence of the bodyweight, the ploidy status (diploid versus triploid) and the water temperature (10 °C versus 16 °C).
A cross-over design was used with 361 trout (median bodyweight: 389 g), each fish receiving OTC intravenously (8–30 mg/kg) and orally (50–150 mg/kg), by gavage or by spontaneous intake via a coating of OTC on the feed to mimic farming practice. Each fish, for each modality, was sampled 3–4 times over a period of 11 days, to establish its individual PK profile. Coated feed and plasma samples were assayed using a sensitive HPLC-MS/MS method. A population PK modelling approach was used to analyse plasma data and estimate key PK parameters and their variability.
A bi-compartmental PK model best described the plasma data. The absolute oral bioavailability appeared to be very low (around 3 %) and the elimination of OTC was slow and strongly influenced by temperature (elimination half-life approximately 79 h at 16 °C versus 113 h at 10 °C). A comparison of spontaneous intake and gavage showed a significant loss of antibiotic due to leaching (about 30 %). Bodyweight and water temperature were the most influential covariates affecting the PK of OTC compared to the effect of ploidy. Pharmacodynamic (PD) studies with OTC against the major trout pathogens are now required to allow a more robust assessment of the expected efficacy thanks to a PK/PD approach.
{"title":"Population pharmacokinetic modelling of oxytetracycline in rainbow trout (Oncorhynchus mykiss): Effects of route of administration, temperature and ploidy","authors":"Alexis Viel , Florine Bachelet , Annaëlle Chailleux , Céline David , Lionel Pineau , Ségolène Calvez , Antoine Rostang","doi":"10.1016/j.aquaculture.2025.742917","DOIUrl":"10.1016/j.aquaculture.2025.742917","url":null,"abstract":"<div><div>The aim of this study was to perform a pharmacokinetic (PK) study of oxytetracycline (OTC) in rainbow trout using different routes of administration and different doses, and to investigate the influence of the bodyweight, the ploidy status (diploid <em>versus</em> triploid) and the water temperature (10 °C <em>versus</em> 16 °C).</div><div>A cross-over design was used with 361 trout (median bodyweight: 389 g), each fish receiving OTC intravenously (8–30 mg/kg) and orally (50–150 mg/kg), by gavage or by spontaneous intake <em>via</em> a coating of OTC on the feed to mimic farming practice. Each fish, for each modality, was sampled 3–4 times over a period of 11 days, to establish its individual PK profile. Coated feed and plasma samples were assayed using a sensitive HPLC-MS/MS method. A population PK modelling approach was used to analyse plasma data and estimate key PK parameters and their variability.</div><div>A bi-compartmental PK model best described the plasma data. The absolute oral bioavailability appeared to be very low (around 3 %) and the elimination of OTC was slow and strongly influenced by temperature (elimination half-life approximately 79 h at 16 °C <em>versus</em> 113 h at 10 °C). A comparison of spontaneous intake and gavage showed a significant loss of antibiotic due to leaching (about 30 %). Bodyweight and water temperature were the most influential covariates affecting the PK of OTC compared to the effect of ploidy. Pharmacodynamic (PD) studies with OTC against the major trout pathogens are now required to allow a more robust assessment of the expected efficacy thanks to a PK/PD approach.</div></div>","PeriodicalId":8375,"journal":{"name":"Aquaculture","volume":"610 ","pages":"Article 742917"},"PeriodicalIF":3.9,"publicationDate":"2026-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144579906","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"农林科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-10-30Epub Date: 2025-06-24DOI: 10.1016/j.aquaculture.2025.742889
Ping Li , Bianhao Zeng , Xuqian Cao , Bin Liu , Ling Liu , Yi Chai , Zhi-Hua Li
Enrofloxacin is one of the antibiotics commonly used in aquaculture. Nevertheless, the precise mechanisms underlying its toxicological effects on the energy metabolism of organisms remain elusive. Therefore, we conducted experiments employing grass carp (Ctenopharyngodon idellus) as our model organism, subjecting them to varying concentrations of ENR for a duration of 21 days followed by a 14-day purification period. Our results revealed that ENR exposure led to disturbances in the intestinal flora of grass carp, inducing hypoglycemia by impeding gluconeogenesis while promoting glycolysis and aerobic metabolism. Additionally, it curtailed lipid utilization and catabolism in grass carp, resulting in hepatic function impairment and metabolic disorders. The effects were partially alleviated after a 14-day purification period, but the damage to the grass carp continued. Furthermore, our investigation unveiled a significant association between the top 20 abundant genera and biomarkers of energy metabolism, providing further insights into the intricate interplay of the microbial-gut-liver axis. Concurrently, we detected 6 common quinolone resistance genes in the experimental group, indicating a potential risk of antimicrobial resistance genes (ARGs) transmission, which could lead to environmental pollution and pose threats to human health.
{"title":"The effect of enrofloxacin exposure on energy metabolism and the ARGs transmission in grass carp: Potential contribution of microbiota-gut-liver axis","authors":"Ping Li , Bianhao Zeng , Xuqian Cao , Bin Liu , Ling Liu , Yi Chai , Zhi-Hua Li","doi":"10.1016/j.aquaculture.2025.742889","DOIUrl":"10.1016/j.aquaculture.2025.742889","url":null,"abstract":"<div><div>Enrofloxacin is one of the antibiotics commonly used in aquaculture. Nevertheless, the precise mechanisms underlying its toxicological effects on the energy metabolism of organisms remain elusive. Therefore, we conducted experiments employing grass carp (<em>Ctenopharyngodon idellus</em>) as our model organism, subjecting them to varying concentrations of ENR for a duration of 21 days followed by a 14-day purification period. Our results revealed that ENR exposure led to disturbances in the intestinal flora of grass carp, inducing hypoglycemia by impeding gluconeogenesis while promoting glycolysis and aerobic metabolism. Additionally, it curtailed lipid utilization and catabolism in grass carp, resulting in hepatic function impairment and metabolic disorders. The effects were partially alleviated after a 14-day purification period, but the damage to the grass carp continued. Furthermore, our investigation unveiled a significant association between the top 20 abundant genera and biomarkers of energy metabolism, providing further insights into the intricate interplay of the microbial-gut-liver axis. Concurrently, we detected 6 common quinolone resistance genes in the experimental group, indicating a potential risk of antimicrobial resistance genes (ARGs) transmission, which could lead to environmental pollution and pose threats to human health.</div></div>","PeriodicalId":8375,"journal":{"name":"Aquaculture","volume":"610 ","pages":"Article 742889"},"PeriodicalIF":3.9,"publicationDate":"2026-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144502055","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"农林科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-10-30Epub Date: 2025-06-25DOI: 10.1016/j.aquaculture.2025.742892
Mette J. Tollervey , Saif Agha , Michaël Bekaert , Almas A. Gheyas , Ross D. Houston , Andrea Doeschl-Wilson , Ashie Norris , Herve Migaud , Alejandro P. Gutierrez , Monica B. Betancor
Atlantic salmon, Salmo salar, have traditionally been reared in net-pens in freshwater (FW) lochs up to smoltification, with subsequent transfer to saltwater (SW) cages for grow-out. Recently, interest in recirculating aquaculture systems (RAS) has grown due to environmental and husbandry benefits. To investigate the impact of RAS on their production cycle, we conducted an experiment under commercial conditions, raising a group of salmon in either a FW-RAS or -loch system. The study evaluated the effects of FW-rearing on SW performance by investigating phenotypic performance, genetic architecture, and genotype-environment interactions (GxE), which describe how the effects of different genotypes on traits change with environmental variation, potentially impacting performance across systems. We co-reared salmon for approximately nine-months before splitting them: half remained in FW-RAS and half transferred to FW-loch, where they were separated for about eight weeks. Both groups were then transferred to a SW cage-site. We sampled fish at the end of FW-rearing as smolts and three-months post-SW transfer as post-smolts, taking fin clips for genotyping. Results indicate that RAS-reared smolts were smaller in FW but demonstrated enhanced growth and lower trait variance post-transfer. Sexually dimorphic growth was observed in the loch population. Heritability of morphological traits increased post-SW transfer in the loch population but decreased in RAS. GxE for SW morphological traits were minimal, though significant genotype re-ranking was observed for SW growth. Genetic correlations between FW and SW morphological traits were high, except for whole-body weight in the loch population. These findings indicate that RAS-origin post-smolts, despite smaller FW size, showed faster growth and reduced phenotypic variance in SW compared to loch-origin fish. Differences in heritability estimates and genotype re-ranking for SW growth suggest that breeding programs may need to refine selection strategies for varied rearing environments.
{"title":"Impact of freshwater rearing on saltwater performance: A genotype-environment interaction study in Atlantic Salmon (Salmo salar)","authors":"Mette J. Tollervey , Saif Agha , Michaël Bekaert , Almas A. Gheyas , Ross D. Houston , Andrea Doeschl-Wilson , Ashie Norris , Herve Migaud , Alejandro P. Gutierrez , Monica B. Betancor","doi":"10.1016/j.aquaculture.2025.742892","DOIUrl":"10.1016/j.aquaculture.2025.742892","url":null,"abstract":"<div><div>Atlantic salmon, <em>Salmo salar,</em> have traditionally been reared in net-pens in freshwater (FW) lochs up to smoltification, with subsequent transfer to saltwater (SW) cages for grow-out. Recently, interest in recirculating aquaculture systems (RAS) has grown due to environmental and husbandry benefits. To investigate the impact of RAS on their production cycle, we conducted an experiment under commercial conditions, raising a group of salmon in either a FW-RAS or -loch system. The study evaluated the effects of FW-rearing on SW performance by investigating phenotypic performance, genetic architecture, and genotype-environment interactions (GxE), which describe how the effects of different genotypes on traits change with environmental variation, potentially impacting performance across systems. We co-reared salmon for approximately nine-months before splitting them: half remained in FW-RAS and half transferred to FW-loch, where they were separated for about eight weeks. Both groups were then transferred to a SW cage-site. We sampled fish at the end of FW-rearing as smolts and three-months post-SW transfer as post-smolts, taking fin clips for genotyping. Results indicate that RAS-reared smolts were smaller in FW but demonstrated enhanced growth and lower trait variance post-transfer. Sexually dimorphic growth was observed in the loch population. Heritability of morphological traits increased post-SW transfer in the loch population but decreased in RAS. GxE for SW morphological traits were minimal, though significant genotype re-ranking was observed for SW growth. Genetic correlations between FW and SW morphological traits were high, except for whole-body weight in the loch population. These findings indicate that RAS-origin post-smolts, despite smaller FW size, showed faster growth and reduced phenotypic variance in SW compared to loch-origin fish. Differences in heritability estimates and genotype re-ranking for SW growth suggest that breeding programs may need to refine selection strategies for varied rearing environments.</div></div>","PeriodicalId":8375,"journal":{"name":"Aquaculture","volume":"610 ","pages":"Article 742892"},"PeriodicalIF":3.9,"publicationDate":"2026-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144557227","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"农林科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-10-30Epub Date: 2025-07-02DOI: 10.1016/j.aquaculture.2025.742925
Baoyu Zhang , Youshen Li , Jianxin Li , Yu Zhai , Ziyu Meng , Xiyue Huang , Yuanyuan Zhou , Jingqun Ao , Ruoyu Liu , Xinhua Chen
Pseudomonas plecoglossicida is a pathogen bacterium responsible for visceral white spot disease (VWND) in Large Yellow Croakers (Larimichthys crocea), causing significant economic losses in commercial fish farms. The proline-alanine-alanine-arginine repeats protein (PAAR) is a core component of the spike structure in the type VI secretion system (T6SS), which injects toxic effectors into host and contributes to bacterial virulence. However, the role of the PAAR gene in P. plecoglossicida and its impact on bacterial infection and host immune responses remain unexplored. In this study, PAAR-1 was identified for the first time in P. plecoglossicida as an effector gene within the T6SS-1 gene cluster, which is regulated and secreted by T6SS-1. The P. plecoglossicida mutant strain (ΔPAAR-1) and its complementary strain (C-ΔPAAR-1) were constructed for subsequent investigation. Compared to the wild-type strain, ΔPAAR-1 exhibited reduced biofilm formation, adhesion, total antioxidant capacity, and secretion of T6SS core protein Hcp-1. In vitro, ΔPAAR-1 showed decreased survival rates in Large Yellow Croaker macrophage cell line (LYC-FM) due to impaired oxidative stress tolerance. In vivo, infection with ΔPAAR-1 led to a significant reduction in mortality, bacterial colonization, and the formation of spleen nodules in Large Yellow Croakers. Comparative transcriptome analysis revealed that PAAR-1 predominantly influences the host Toll-like receptor (TLR) signaling pathway and apoptosis by upregulating the expression of plasma membrane-associated TLRs, including TLR1, TLR2, and TLR5, while downregulating the expression of endosomal TLRs like TLR3, TLR7, TLR8, and TLR9, along with its downstream molecules such as MyD88 and TRAF3. Additionally, knockout PAAR-1 downregulates apoptosis-related genes including AP-1, NF-κB, FAS-L TNFα, Caspase8, and FAS-L. Real-time quantitative polymerase chain reaction (RT-qPCR) further confirmed these findings. Furthermore, the proportion of apoptotic cells was significantly lower in the ΔPAAR-1 infected LYC-PKM cells. These results indicate that PAAR-1 is involved in regulating TLR signaling pathway and apoptosis in Large Yellow Croaker. This study provides the first identification of the core T6SS-1 gene PAAR-1 in P. plecoglossicida, offering valuable insights into its pathogenic mechanisms and presenting a potential target for attenuated vaccine development.
{"title":"Identification and characterization of the PAAR-1 gene in Pseudomonas plecoglossicida: Insights into bacterial phenotypes and host immune responses in Large Yellow Croaker (Larimichthys crocea)","authors":"Baoyu Zhang , Youshen Li , Jianxin Li , Yu Zhai , Ziyu Meng , Xiyue Huang , Yuanyuan Zhou , Jingqun Ao , Ruoyu Liu , Xinhua Chen","doi":"10.1016/j.aquaculture.2025.742925","DOIUrl":"10.1016/j.aquaculture.2025.742925","url":null,"abstract":"<div><div><em>Pseudomonas plecoglossicida</em> is a pathogen bacterium responsible for visceral white spot disease (VWND) in Large Yellow Croakers (<em>Larimichthys crocea</em>), causing significant economic losses in commercial fish farms. The proline-alanine-alanine-arginine repeats protein (PAAR) is a core component of the spike structure in the type VI secretion system (T6SS), which injects toxic effectors into host and contributes to bacterial virulence. However, the role of the <em>PAAR</em> gene in <em>P. plecoglossicida</em> and its impact on bacterial infection and host immune responses remain unexplored. In this study, <em>PAAR-1</em> was identified for the first time in <em>P. plecoglossicida</em> as an effector gene within the T6SS-1 gene cluster, which is regulated and secreted by T6SS-1. The <em>P. plecoglossicida</em> mutant strain (Δ<em>PAAR-1</em>) and its complementary strain (C-Δ<em>PAAR-1</em>) were constructed for subsequent investigation. Compared to the wild-type strain, Δ<em>PAAR-1</em> exhibited reduced biofilm formation, adhesion, total antioxidant capacity, and secretion of T6SS core protein Hcp-1. In vitro, Δ<em>PAAR-1</em> showed decreased survival rates in Large Yellow Croaker macrophage cell line (LYC-FM) due to impaired oxidative stress tolerance. In vivo, infection with Δ<em>PAAR-1</em> led to a significant reduction in mortality, bacterial colonization, and the formation of spleen nodules in Large Yellow Croakers. Comparative transcriptome analysis revealed that <em>PAAR-1</em> predominantly influences the host Toll-like receptor (TLR) signaling pathway and apoptosis by upregulating the expression of plasma membrane-associated TLRs, including <em>TLR1</em>, <em>TLR2</em>, and <em>TLR5</em>, while downregulating the expression of endosomal TLRs like <em>TLR3</em>, <em>TLR7</em>, <em>TLR8</em>, and <em>TLR9</em>, along with its downstream molecules such as <em>MyD88</em> and <em>TRAF3.</em> Additionally, knockout <em>PAAR-1</em> downregulates apoptosis-related genes including <em>AP-1, NF-κB, FAS-L TNFα, Caspase8,</em> and <em>FAS-L</em>. Real-time quantitative polymerase chain reaction (RT-qPCR) further confirmed these findings. Furthermore, the proportion of apoptotic cells was significantly lower in the Δ<em>PAAR-1</em> infected LYC-PKM cells. These results indicate that <em>PAAR-1</em> is involved in regulating TLR signaling pathway and apoptosis in Large Yellow Croaker. This study provides the first identification of the core T6SS-1 gene <em>PAAR-1</em> in <em>P. plecoglossicida</em>, offering valuable insights into its pathogenic mechanisms and presenting a potential target for attenuated vaccine development.</div></div>","PeriodicalId":8375,"journal":{"name":"Aquaculture","volume":"610 ","pages":"Article 742925"},"PeriodicalIF":3.9,"publicationDate":"2026-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144557228","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"农林科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ecytonucleospora hepatopenaei (EHP) is a microsporidian parasite associated with growth retardation and size variation in shrimp. In recent years, it has emerged as a serious threat to shrimp aquaculture worldwide. A c-type lysozyme (LvLyz-c) from Pacific white shrimp (Litopenaeus vannamei) has been shown to inhibit EHP spore germination and reduce infectivity. This study investigated the protective effects of dietary supplementation with recombinant LvLyz-c (rLvLyz-c) against EHP infection. After a 14-day feeding trial, gut microbiome analysis revealed increased richness, diversity, and abundance of beneficial bacteria in shrimp fed a basal diet supplemented with rLvLyz-c, compared to those fed a basal diet supplemented with either sodium chloride-Tris-EDTA buffer (control) or commercial hen egg-white lysozyme (HEWL). Additionally, shrimp fed rLvLyz-c supplementation exhibited significantly higher weight gain (p < 0.05), and lower, but not significantly different, feed conversion ratios compared to the control and HEWL groups. Upon EHP infection, shrimp fed rLvLyz-c had significantly lower EHP copy numbers (∼103–104 copies) than those fed basal (∼106 copies) or HEWL (∼106 copies) diets at 12 days post-cohabitation. Supplementation with rLvLyz-c enhanced shrimp health indicators, including total hemocyte counts and intestinal wall thickness. These effects were associated with upregulation of immune-related genes, including LvHSP70, LvHSP90, LvPrx4, LvPEN3, CrustinLv4, and LvLyz-c. Overall, dietary rLvLyz-c supplementation improved gut microbiota composition, growth performance, and immune response in L. vannamei, demonstrating its potential as a feed additive to protect against EHP infection.
肝芽胞核孢子虫（EHP）是一种与虾的生长迟缓和大小变化有关的微孢子虫寄生虫。近年来，它已成为全球对虾养殖的严重威胁。一种来自凡纳滨对虾（Litopenaeus vannamei）的c型溶菌酶（LvLyz-c）已被证明能抑制EHP孢子萌发并降低传染性。本研究探讨了饲粮中添加重组LvLyz-c （rLvLyz-c）对EHP感染的保护作用。经过14天的饲养试验，肠道微生物组分析显示，与在基础饲粮中添加氯化钠- tris - edta缓冲液（对照）或商业蛋清溶菌酶（HEWL）的对虾相比，在基础饲粮中添加rLvLyz-c的对虾肠道有益菌的丰富度、多样性和丰度都有所增加。此外，添加rLvLyz-c的对虾增重显著增加(p <；0.05)，饲料系数低于对照组和HEWL组，但差异不显著。感染EHP后，在同居后12天，饲喂rLvLyz-c的对虾的EHP拷贝数（~ 103-104个拷贝）显著低于饲喂基础饲料（~ 106个拷贝）或HEWL饲料（~ 106个拷贝）的对虾。添加rLvLyz-c可以提高对虾的健康指标，包括总血细胞计数和肠壁厚度。这些作用与免疫相关基因的上调有关，包括LvHSP70、LvHSP90、LvPrx4、LvPEN3、CrustinLv4和LvLyz-c。总体而言，饲粮中添加rLvLyz-c可改善凡纳梅乳杆菌的肠道菌群组成、生长性能和免疫反应，显示其作为饲料添加剂预防EHP感染的潜力。
{"title":"Dietary supplementation with recombinant shrimp c-type lysozyme modulates the gut microbiome and enhances growth performance and resistance to Ecytonucleospora hepatopenaei infection in Pacific white shrimp (Litopenaeus vannamei)","authors":"Nutthapon Sangklai , Pongsakorn Sukonthamarn , Orawan Thepmanee, Pattana Jaroenlak, Anchalee Tassanakajon","doi":"10.1016/j.aquaculture.2025.742884","DOIUrl":"10.1016/j.aquaculture.2025.742884","url":null,"abstract":"<div><div><em>Ecytonucleospora hepatopenaei</em> (EHP) is a microsporidian parasite associated with growth retardation and size variation in shrimp. In recent years, it has emerged as a serious threat to shrimp aquaculture worldwide. A c-type lysozyme (<em>Lv</em>Lyz-c) from Pacific white shrimp (<em>Litopenaeus vannamei</em>) has been shown to inhibit EHP spore germination and reduce infectivity. This study investigated the protective effects of dietary supplementation with recombinant <em>Lv</em>Lyz-c (r<em>Lv</em>Lyz-c) against EHP infection. After a 14-day feeding trial, gut microbiome analysis revealed increased richness, diversity, and abundance of beneficial bacteria in shrimp fed a basal diet supplemented with r<em>Lv</em>Lyz-c, compared to those fed a basal diet supplemented with either sodium chloride-Tris-EDTA buffer (control) or commercial hen egg-white lysozyme (HEWL). Additionally, shrimp fed r<em>Lv</em>Lyz-c supplementation exhibited significantly higher weight gain (<em>p</em> < 0.05), and lower, but not significantly different, feed conversion ratios compared to the control and HEWL groups. Upon EHP infection, shrimp fed r<em>Lv</em>Lyz-c had significantly lower EHP copy numbers (∼10<sup>3</sup>–10<sup>4</sup> copies) than those fed basal (∼10<sup>6</sup> copies) or HEWL (∼10<sup>6</sup> copies) diets at 12 days post-cohabitation. Supplementation with r<em>Lv</em>Lyz-c enhanced shrimp health indicators, including total hemocyte counts and intestinal wall thickness. These effects were associated with upregulation of immune-related genes, including <em>LvHSP70</em>, <em>LvHSP90</em>, <em>LvPrx4</em>, <em>LvPEN3</em>, <em>CrustinLv4</em>, and <em>LvLyz-c.</em> Overall, dietary r<em>Lv</em>Lyz-c supplementation improved gut microbiota composition, growth performance, and immune response in <em>L. vannamei</em>, demonstrating its potential as a feed additive to protect against EHP infection.</div></div>","PeriodicalId":8375,"journal":{"name":"Aquaculture","volume":"610 ","pages":"Article 742884"},"PeriodicalIF":3.9,"publicationDate":"2026-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144523682","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"农林科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-10-30Epub Date: 2025-06-17DOI: 10.1016/j.aquaculture.2025.742864
Luyao Xu , Jiamin Li , Ao Luo , Jiujie Zhou , Samwel M. Limbu , Jialing Xu , Peiyan Lu , Tingting Li , Xiaoxuan Qi , Mo Peng
To comprehensively investigate effects of dietary l-carnitine (LC) on growth performance, lipid metabolism, oxidative stress, mitochondrial function and endoplasmic reticulum (ER) stress in farmed fish fed high-carbohydrate-diets (HCD), 960 rice field eels (17.09 ± 0.14 g) were chosen and randomly assigned to 16 cages. These fish were fed a control diet (15% α-starch, CON), a high-carbohydrate-diet (35% α-starch, HCD), a HCD supplemented with 1.2‰ LC (HC/LLC), and a HCD supplemented with 2.4‰ LC (HC/HLC). Results of 8-week feeding trial showed that HCD increased liver lipid content, induced liver dysfunction, oxidative stress and endoplasmic reticulum (ER) stress, but did not affect growth performance. Dietary LC supplementation increased significantly weight gain rate and specific growth rate and decreased liver lipid content. Concurrently, LC reduced the activity of alanine transaminase enzyme in the serum, improved liver's antioxidant capacity, thereby mitigating liver damage. Dietary LC positively regulated the expression of genes related to oxidative stress, such as Kelch-like ECH-associated protein 1, nuclear factor erythroid 2-related factor 2, catalase and superoxide dismutase in fish. Furthermore, LC supplementation upregulated expression of genes related to the mitochondrial function, such as cardiolipin synthase 1 and lysocardiolipin acyltransferase 1 (cardiolipin metabolism), peroxisome proliferator-activated receptor gamma coactivator 1 alpha, peroxisome proliferator-activated receptor alpha and carnitine palmitoyltransferase 1 (mitochondrial β-oxidation) in fish. Intriguingly, administering LC-fortified diets resulted in downregulation of ER stress-related gene expression, such as glucose regulated protein 78, inositol-requiring enzyme 1 and activating transcription factor 6 in fish. For the first time, this study reports that the incorporation of LC into HCD facilitates lipid metabolism of fish through concurrent enhancement of mitochondrial function, reduction of oxidative stress, and alleviation of ER stress.
{"title":"Effects of dietary l-carnitine on growth performance, lipid metabolism, oxidative stress, mitochondrial function and endoplasmic reticulum stress of rice field eel (Monopterus albus) fed high-carbohydrate-diets","authors":"Luyao Xu , Jiamin Li , Ao Luo , Jiujie Zhou , Samwel M. Limbu , Jialing Xu , Peiyan Lu , Tingting Li , Xiaoxuan Qi , Mo Peng","doi":"10.1016/j.aquaculture.2025.742864","DOIUrl":"10.1016/j.aquaculture.2025.742864","url":null,"abstract":"<div><div>To comprehensively investigate effects of dietary <span>l</span>-carnitine (LC) on growth performance, lipid metabolism, oxidative stress, mitochondrial function and endoplasmic reticulum (ER) stress in farmed fish fed high-carbohydrate-diets (HCD), 960 rice field eels (17.09 ± 0.14 g) were chosen and randomly assigned to 16 cages. These fish were fed a control diet (15% α-starch, CON), a high-carbohydrate-diet (35% α-starch, HCD), a HCD supplemented with 1.2‰ LC (HC/LLC), and a HCD supplemented with 2.4‰ LC (HC/HLC). Results of 8-week feeding trial showed that HCD increased liver lipid content, induced liver dysfunction, oxidative stress and endoplasmic reticulum (ER) stress, but did not affect growth performance. Dietary LC supplementation increased significantly weight gain rate and specific growth rate and decreased liver lipid content. Concurrently, LC reduced the activity of alanine transaminase enzyme in the serum, improved liver's antioxidant capacity, thereby mitigating liver damage. Dietary LC positively regulated the expression of genes related to oxidative stress, such as Kelch-like ECH-associated protein 1, nuclear factor erythroid 2-related factor 2, catalase and superoxide dismutase in fish. Furthermore, LC supplementation upregulated expression of genes related to the mitochondrial function, such as cardiolipin synthase 1 and lysocardiolipin acyltransferase 1 (cardiolipin metabolism)<em>,</em> peroxisome proliferator-activated receptor gamma coactivator 1 alpha<em>,</em> peroxisome proliferator-activated receptor alpha and carnitine palmitoyltransferase 1 (mitochondrial β-oxidation) in fish<em>.</em> Intriguingly, administering LC-fortified diets resulted in downregulation of ER stress-related gene expression, such as glucose regulated protein 78<em>,</em> inositol-requiring enzyme 1 and activating transcription factor 6 in fish. For the first time, this study reports that the incorporation of LC into HCD facilitates lipid metabolism of fish through concurrent enhancement of mitochondrial function, reduction of oxidative stress, and alleviation of ER stress.</div></div>","PeriodicalId":8375,"journal":{"name":"Aquaculture","volume":"610 ","pages":"Article 742864"},"PeriodicalIF":3.9,"publicationDate":"2026-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144523683","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"农林科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This study describes the temporal and spatial dynamics of microbiota composition, water quality parameters and fish health status in a commercial Recirculating Aquaculture System (RAS) for yellowtail kingfish (Seriola lalandi) spanning from April to November 2021. Water quality was effectively controlled, with key parameters such as CO2, pH, temperature, nitrogen compounds and hydrogen sulfide (H2S) consistently maintained within safety thresholds reported in the literature. Microbiota composition was analyzed in various fish tissues and RAS components using 16S rRNA gene amplicon sequencing. The predominant genera in RAS samples (tank water, tank wall biofilm, biofilter biofilm, and denitrification unit) included Erythrobacter, Glaciecola, and Nitrospira. In contrast, fish tissue samples (gills, intestine, and skin) were mainly colonized by Aliivibrio, Pseudomonas, and an uncultured genus from the Mycoplasmataceae family. Cluster analysis revealed similarities in bacterial composition between tank water and external fish tissues (skin and gills), with variations over time corresponding to changes in water parameters. Digital PCR assays were developed to target specific fish pathogens such as Vibrio harveyi, Vibrio anguillarum, and Photobacterium damselae piscicida, revealing low or undetectable pathogen levels throughout most of the monitoring period. In tank water, these species showed the highest concentration in August and September. A Multiparametric Semi-quantitative Scoring System (MSSS) was developed for histological examination of gills, intestine, liver, spleen, and kidney. Increased inflammation coincided with higher pathogen presence in the water. However, no clinical signs of vibriosis or pasteurellosis were detected, indicating overall good fish health and a robust immune system. This integrated approach - combining innovative pathogen-specific digital PCR assays, MSSS histological scoring and microbiota profiling offers a valuable framework for monitoring fish health and optimizing production quality in kingfish farming within RAS environments.
{"title":"Health, microbiota, and water quality analysis: A case study in a commercial recirculating aquaculture system for yellowtail kingfish (Seriola lalandi).","authors":"Katerina Loufi , Julia Hassa , Eric Hernández , Marit Stormoen , Deni Ribičić , Stamatios Kapasakis , Tobias Busche , Jörn Kalinowski , Pavlos Makridis , Roman Netzer , Elia Ciani","doi":"10.1016/j.aquaculture.2025.742851","DOIUrl":"10.1016/j.aquaculture.2025.742851","url":null,"abstract":"<div><div>This study describes the temporal and spatial dynamics of microbiota composition, water quality parameters and fish health status in a commercial Recirculating Aquaculture System (RAS) for yellowtail kingfish (<em>Seriola lalandi</em>) spanning from April to November 2021. Water quality was effectively controlled, with key parameters such as CO<sub>2</sub>, pH, temperature, nitrogen compounds and hydrogen sulfide (H<sub>2</sub>S) consistently maintained within safety thresholds reported in the literature. Microbiota composition was analyzed in various fish tissues and RAS components using 16S rRNA gene amplicon sequencing. The predominant genera in RAS samples (tank water, tank wall biofilm, biofilter biofilm, and denitrification unit) included <em>Erythrobacter</em>, <em>Glaciecola</em>, and <em>Nitrospira</em>. In contrast, fish tissue samples (gills, intestine, and skin) were mainly colonized by <em>Aliivibrio</em>, <em>Pseudomonas</em>, and an uncultured genus from the <em>Mycoplasmataceae</em> family. Cluster analysis revealed similarities in bacterial composition between tank water and external fish tissues (skin and gills), with variations over time corresponding to changes in water parameters. Digital PCR assays were developed to target specific fish pathogens such as <em>Vibrio harveyi</em>, <em>Vibrio anguillarum</em>, and <em>Photobacterium damselae piscicida</em>, revealing low or undetectable pathogen levels throughout most of the monitoring period. In tank water, these species showed the highest concentration in August and September. A Multiparametric Semi-quantitative Scoring System (MSSS) was developed for histological examination of gills, intestine, liver, spleen, and kidney. Increased inflammation coincided with higher pathogen presence in the water. However, no clinical signs of vibriosis or pasteurellosis were detected, indicating overall good fish health and a robust immune system. This integrated approach - combining innovative pathogen-specific digital PCR assays, MSSS histological scoring and microbiota profiling offers a valuable framework for monitoring fish health and optimizing production quality in kingfish farming within RAS environments.</div></div>","PeriodicalId":8375,"journal":{"name":"Aquaculture","volume":"610 ","pages":"Article 742851"},"PeriodicalIF":3.9,"publicationDate":"2026-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144490321","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"农林科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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