Author: marina02

classification of post-delousing mortality in farmed atlantic salmon: a case study

introduction

mechanical delousing, a common practice in norwegian salmon farming, is frequently reported as a significant cause of mortality. however, there is limited knowledge about the accuracy and quality of causal mortality recordings for these operations. this study aimed to identify the underlying causes for mortality following a mechanical delousing through macroscopic pathological examination.

methods

the study was conducted on three net-pen populations of atlantic salmon. a total of 453 dead fish were necropsied at four time points: 1 day before, 1 day after (first collection of dead fish after delousing), 3-4 days after, and 11-13 days after delousing. macroscopic pathology was recorded. necropsy findings, along with clinical history at the facility, were used to assign each fish a cause of death according to the standard for cause-specific mortality and loss (1).

results

mortality assignments revealed that nearly 90% of the necropsied fish died due to handling or delousing on day 1 and day 3-4 after delousing. this percentage decreased to about 50% on day 11-13 after delousing. the study also found inconsistencies between cause-specific mortality assignments at necropsy and daily mortality recordings by farmers, implying that current practices may underestimate the long-term negative effects of delousing.

cerebral haemorrhages were observed in approximately 25% of the necropsied fish 1 day after delousing. dead fish with pathological changes assumed related to delousing, including brain haemorrhage, were observed until the end of the study period.

conclusion

the findings indicate that mechanical delousing procedures can lead to mortality and pathological changes up to 13 days after the procedure. guidelines for recording mortality causes following delousing are necessary to ensure data comparability and accurate identification of underlying mortality causes. the occurrence of cerebral haemorrhages suggests that fish are exposed to significant trauma during the delousing procedures.

references

aunsmo, a., persson, d., stormoen, m., romstad, s., jamtøy, o., & midtlyng, p. (2023). real-time monitoring of cause-specific mortality- and losses in industrial salmon farming. aquaculture, 563, 738969. doi:10.1016/j.aquaculture.2022.738969

1. RINGSTAD, NANNA KRISTINE, NMBU, Presenter
2. PERSSON, DAVID, NMBU, Author
3. STORMOEN, MARIT, NMBU, Author
4. MIDTLYNG, PAUL JOHAN, NMBU, Author

Immunological role of beta-defensins in European sea bass immunity

Introduction
Antimicrobial peptides (AMPs) are small, cationic, and amphipathic peptides with predominant alpha-helix secondary structure. AMPs show a dual mode of action: i) direct lytic effects, and ii) modulation of the host immune response. AMPs are known to regulate inflammatory responses, induce leucocyte mobilization and connect innate and adaptive responses. Among the AMPs, we can find beta-defensins (Bdef). In European sea bass (Dicentrarchus labrax), a commercial species, Bdef1 and Bdef2 have been described but their roles in immunity have not been explored yet. This work evaluated the immunomodulatory role of synthetic Bdefs and their potential application in functional diets.
Methodology
European sea bass head-kidney leucocytes (HKLs) were stimulated with synthetic Bdef1 and Bdef2 for 24 h. Respiratory burst activity and transcription of immune-related genes were determined. For the in vivo trial, synthetic Bdef1 was encapsulated in alginate–chitosan nanoparticles (NPs) and administered orally to European sea bass juveniles for 5 days. On day 6th, brain, head-kidney, and hindgut were collected for subsequent analysis of immune-related gene expression by qPCR while serum samples were used to evaluate the bactericidal activity or Bdef levels.
Results
In vitro studies revealed that the respiratory burst was not primed and only Bdef1 was able to up-regulate the transcription of immune genes. Concretely, Bdef1 up-regulated genes involved in the antiviral response, cell-mediated cytotoxicity, and inflammation. Thus, Bdef1 was selected to be included in a functional diet. Unfortunately, oral administration of encapsulated Bdef1 did not enhance serum bactericidal activity nor Bdef levels and at gene expression level we only observed the down-regulation of il1b transcription in head-kidney.
Conclusions
As well as in previous studies, our in vitro studies also demonstrated that Bdef1, and not Bdef2, shows immunomodulatory actions. Therefore, Bdef1 could be proposed as an immunostimulant agent with potential in aquaculture. Thus, more studies are mandatory to ascertain how Bdef1 might be orally administered and their application in aquaculture.

Funding: PID2022-139492NB-I00 funded by MICIU/AEI/10.13039/501100011033 and by ERDF/EU to AC, 22651/PI/24 funded by FSRM/10.13039/100007801, PRE2020-093771 to LC, RYC2021-034184-I to MCG, IJC2020-042733-I from MICIU/AEI/10.13039/501100011033 and by the European Union NextGenerationEU/PRTR to YV. This study forms part of the ThinkInAzul programme and was supported by MCIU with funding from European Union NextGenerationEU (PRTR-C17.I1) and by Comunidad Autónoma de la Región de Murcia – Fundación Séneca to AC and EH.

1. CUESTA, ALBERTO, UNIVERSIDAD MURCIA, Presenter
2. HERNÁNDEZ, ELENA, UNIVERSIDAD MURCIA, Author
3. CERVERA, LAURA, UNIVERSIDAD MURCIA, Author
4. FERNÁNDEZ-HERNÁNDEZ, FRANCISCO J., UNIVERSIDAD MURCIA, Author
5. COLLADO-GONZÁLEZ, MAR, UNIVERSIDAD MURCIA, Author
6. CÁRDENAS, CONSTANZA, PONTIFICIA UNIVERSIDAD CATÓLICA DE VALPARAÍSO, Author
7. GUZMÁN, FANNY, PONTIFICIA UNIVERSIDAD CATÓLICA DE VALPARAÍSO, Author
8. MERCADO, LUIS, PONTIFICIA UNIVERSIDAD CATÓLICA DE VALPARAÍSO, Author
9. VALERO, YULEMA, UNIVERSIDAD MURCIA, Author
10. CHAVES-POZO, ELENA, Centro Oceanográfico de Murcia (COMU-IEO), CSIC, Author

European sea bass beta-defensin is involved in anti-NNV response but its oral administration did not elicit any immunomodulation

Introduction
Antimicrobial peptides (AMPs) are short aminoacidic sequences with promising applications in field like medicine or aquaculture. AMPs can act as direct lytic effectors against a wide range of pathogens, including viruses, and modulate the immune response. Among the most relevant viruses in the Mediterranean area, Betanodavirus (Betanodaviridae; NNV) causes the viral retinopathy and encephalopathy in fish, being European sea bass (Dicentrarchus labrax) one of the most susceptible species. In this work, we aimed to evaluate the implication of European sea bass beta-defensins (Bdef) AMPs during NNV infections and their preventive roles against NNV when administered in diet.
Methodology
European sea bass were intramuscularly infected with NNV and sampled at 1, 7 and 15 days post-infection (dpi) for Bdef gene and protein analysis. Afterwards, sea bass juveniles were fed with synthetic Bdef1 encapsulated in alginate-chitosan nanoparticles (NP) for 5 days, and then challenged with a sublethal dose of NNV. Mortality and immunity were recorded.
Results
During in vivo NNV infection, only bdef1 transcripts were up-regulated in brain and in HK, while bdef2 transcripts were not altered. Moreover, elevated Bdef levels were detected in serum and brain upon infection by ELISA. By contrast, upon NNV-infection, oral administration of synthetic Bdef1 resulted in unaltered immune parameters in sea bass when compared to NNV-infected alone.
Conclusions
This work shows the implication of Bdef in the response against NNV, mainly bdef1. Despite Bdef1 role in the anti-NNV response, its administration via diet did not stimulate the immune response elicited by the virus alone. More efforts are needed to characterize Bdef1 functionality for its application in aquaculture.
Funding: PID2022-139492NB-I00 funded by MICIU/AEI/10.13039/501100011033 and by ERDF/EU to AC, 22651/PI/24 funded by FSRM/10.13039/100007801, PRE2020-093771 to LC, RYC2021-034184-I to MCG, IJC2020-042733-I from MICIU/AEI/10.13039/501100011033 and by the European Union NextGenerationEU/PRTR to YV. This study forms part of the ThinkInAzul programme and was supported by MCIU with funding from European Union NextGenerationEU (PRTR-C17.I1) and by Comunidad Autónoma de la Región de Murcia – Fundación Séneca to AC and EH.

1. CUESTA, ALBERTO, UNIVERSIDAD MURCIA, Presenter
2. FERNÁNDEZ-HERNÁNDEZ, FRANCISCO J., UNIVERSIDAD MURCIA, Author
3. CERVERA, LAURA, UNIVERSIDAD MURCIA, Author
4. HERNÁNDEZ, ELENA, UNIVERSIDAD MURCIA, Author
5. COLLADO-GONZÁLEZ, MAR, UNIVERSIDAD MURCIA, Author
6. CÁRDENAS, CONSTANZA, PONTIFICIA UNIVERSIDAD CATÓLICA DE VALPARAÍSO, Author
7. GUZMÁN, FANNY, PONTIFICIA UNIVERSIDAD CATÓLICA DE VALPARAÍSO, Author
8. MERCADO, LUIS, PONTIFICIA UNIVERSIDAD CATÓLICA DE VALPARAÍSO, Author
9. VALERO, YULEMA, UNIVERSIDAD MURCIA, Author
10. CHAVES-POZO, ELENA, Centro Oceanográfico de Murcia (COMU-IEO), CSIC, Author

Dietary efficacy of immune modulator during cold stress in the Mediterranean species gilthead seabream (Sparus aurata)

Gilthead seabream (Sparus aurata) is frequently affected by seasonal stress in Mediterranean aquaculture, particularly when water temperatures fall below 15 °C or rise above 30 °C. The cold-water condition, commonly known as winter syndrome, leads to metabolic depression, reduced feed intake, immunosuppression, and increased disease susceptibility, posing a significant challenge to fish health and farm productivity. Dietary immune modulators are therefore considered a strategic approach to mitigate these effects. AQUASTIM (Adisseo) is a yeast extract–based synergistic blend combined with other functional ingredients, designed to provide broad immunomodulatory support. This combination aims to maintain immunocompetence during complex stress scenarios and high-risk periods.

This study evaluated the efficacy of AQUASTIM (3 kg/T) in comparison to commonly used immunostimulants, β-glucan (3 kg/T) and mannan oligosaccharides (MOS, 3 kg/T), in gilthead seabream exposed to cold stress. Fish (347 ± 10 g) were fed experimental diets over 31 days while gradually acclimated from 26 °C to 18 °C. Immune and antioxidant responses were assessed in the head kidney and serum using biomarkers related to cell survival, inflammatory regulation, and oxidative defense. In addition, intestinal histology was evaluated as an indicator of gut health under cold stress conditions. AQUASTIM significantly preserved growth performance under cold stress, with a 32% improvement in weight gain, a 41% increase in specific growth rate, and a 16% reduction in FCR compared to the control. Moreover, these improvements outperformed both β-glucan and MOS. At the molecular level, AQUASTIM significantly upregulated the expression of CK1, IL-10, IL-1β, and MnSOD in the head kidney. In serum, bactericidal activity increased approximately twofold, while complement and lysozyme activities showed numerical enhancement. Improvements in intestinal health were also evident, with a 58% increase in mucosal surface area in the midgut, 26% in the hindgut, and a 33% increase in mucus cell density, indicating enhanced gut barrier integrity and mucosal protection under stress conditions.

Overall, these findings validate the use of a dietary synergistic immunomodulatory blend to enhance disease resilience and maintain performance in gilthead seabream under cold stress, offering a practical nutritional solution to mitigate the impacts of winter syndrome in Mediterranean aquaculture.

1. CHEN, I-TUNG, Adisseo France SAS, Presenter
2. ISERN-SUBICH, MARIA MERCÈ, Adisseo France SAS, Author
3. NUEZ-ORTÍN, WALDO G., Adisseo France SAS, Author

ANTI-BETANODAVIRUS ACTIVITY OF NATURAL SUBSTANCES OBTAINED FROM BACTERIA AND ALGAE

Introduction
Nervous necrosis virus (NNV) infects a wide range of fish species, causing high mortality rates in cultured fish. A prophylactic practise to enhance the natural resistance of farmed fish to viral infections is the use of functional food. Extracellular products (ECPs) from probiotic bacteria represent a valid and safe strategy for providing beneficial effects against microorganisms in fish. Algae are also sources of substances with potential activity to improve resistance to infections. The objective of this study was to evaluate the antiviral activity of ECPs from the probiotic bacteria Shewanella putrefaciens Pdp11 and Bacillus pumilus UMA169, as well as of extracts and polysaccharides from Ulva rigida against a RGNNV isolate, the most prevalent genotype in Mediterranean outbreaks. 

Methodology
E11 cells were inoculated at 0.05 MOI, and the cellular survival rate was calculated using the MTT reduction assay at 5 days post-infection. The substances tested were: (i) ECPs from B. pumilus UMA169 and S. putrefaciens Pdp11 (both cultured on TSAs at 15 ºC for 48 h) at 50 μg of protein·mL-1, (ii) extracts of U. rigida at 100 and 500 μg·mL-1 and (iii) ulvan polysaccharides from U. rigida at 50 μg·mL-1.

Results
ECPs from B. pumilus UMA169 and Pdp11, exhibited antiviral activity against RGNNV. Actually, both ECPs conferred full protection to the cells. Furthermore, when E11 cells were inoculated with these two ECPs, a higher number of cells was recorded, thus suggesting that these compounds could stimulate cell growth. 
Regarding extracts and polysaccharides from U. rigida, a clear protection effect was recorded in cells treated with ulvan polysaccharides, although the protection was lower than the observed with ECPs. In contrast, extracts of U. rigida showed the opposite effect, that is, cellular survival of RGNNV infected cells was lower in the presence of the extract than in control cells.

Conclusions
ECPs and ulvans are promising candidates to be used as protective substances against RGNNV. Actually, their effect on viral replication and infective viral particles production, will also be evaluated. An in vivo assay will also be performed.

Acknowledgments
Project PCM_000035, from the "Next Generation EU" Recovery Fund through the Recovery, Transformation and Resilience Plan” and co-funded by the Regional Government of Andalusia. The opinions expressed are solely those of the author(s) and do not necessarily reflect those of the European Union or the European Commission. The European Union and the European Commission are not responsible of these opinions.

1. BÉJAR, JULIA, UNIVERSITY OF MALAGA, Presenter
2. Ravina, Candela, UNIVERSITY OF MALAGA, Author
3. Abdala-Díaz, Roberto T., UNIVERSITY OF MALAGA, Author
4. Arijo, Salvador, UNIVERSITY OF MALAGA, Author
5. García-Rosado, Esther, UNIVERSITY OF MALAGA, Author
6. Alonso, M. Carmen, UNIVERSITY OF MALAGA, Author

The effect of Lactiplantibacillus probiotic supplement on rainbow trout challenged with Aeromonas salmonicida

Introduction
Aeromonas salmonicida is one of the most relevant aquatic pathogens leading to significant economic loss in salmonid aquaculture due to mass morbidity and mortality. We aimed to verify the effect of dietary supplementation with Lactiplantibacillus plantarum strain isolated from intestine of healthy fish on rainbow trout challenged with A. salmonicida. In order to decrease economic burden associated with permanent dietary supplementation in commercial aquaculture, also the potential of cyclic supplementation was tested.
Methodology
Control fish (C) were fed for 7 weeks by commercial feed, another group (P) was provided this feed with added bacterial cells of L. plantarum R2 Biocenol™ and the third group (PC) was fed with the enriched feed for 4 weeks, followed by 3 weeks of control feed. Then all fish were challenged with A. salmonicida via bath and subsequently provided normal diet (C) or probiotic supplemented diet (P, PC) till the end of the experiment. Sampling was performed 1 week and 3 weeks after the challenge. Mortality, gut microbiota, immunological, haematological and plasma biochemical parameters were assessed.
Results
Neither of the strategies of probiotic supplementation enhanced survival of the challenged fish. One week after the challenge, no significant differences were found regarding most haematological, plasma biochemical and immune parameters with the exception of decreased lymphocyte count in fish supplemented in cycles. Two weeks later, a decline in total and relative count of phagocytes was revealed in the same group. Level of IgM was significantly lower both in P and PC groups when compared to the control, while decreased IL-10 and a rise in total protein were found only in PC group. Gut microbiome analysis has not been finished yet.
Conclusions
Either continuous or cyclic dietary supplementation with the autochthonous strain did not result in improvement of survival rate after challenge with A. salmonicida. Microbiome analysis, which is currently being processed, could elucidate the context and provide several answers to arising questions. The importance of in vivo challenge tests with potential probiotic strains has been demonstrated.
The study was funded by the projects PROFISH CZ.02.1.01/0.0/0.0/16_019/0000869 and FVHE/Pikula/2025ITA22.

1. MIKULÍKOVÁ, IVANA, UNIVERSITY OF VETERINARY SCIENCES BRNO, Czech Republic; Mendel University in Brno, Czech Republic, Presenter
2. Banďouchová, Hana, University of Veterinary Sciences Brno, Czech Republic; Mendel University in Brno, Czech Republic, Author
3. Blahová, Jana, University of Veterinary Sciences Brno, Czech Republic, Author
4. Papežíková, Ivana, UNIVERSITY OF VETERINARY SCIENCES BRNO, Czech Republic; Mendel University in Brno, Czech Republic, Author
5. Novotná, Hana, UNIVERSITY OF VETERINARY SCIENCES BRNO; Mendel University in Brno; Veterinary Research Institute, Czech Republic, Author
6. Lepková, Zuzana, University of Veterinary Sciences Brno, Czech Republic, Author
7. Toulová, Ivona, UNIVERSITY OF VETERINARY SCIENCES BRNO, Czech Republic; Mendel University in Brno, Czech Republic, Author
8. Radojičić, Marija, Mendel University in Brno, Czech Republic, Author
9. Palíková, Miroslava, UNIVERSITY OF VETERINARY SCIENCES BRNO, Czech Republic; Mendel University in Brno, Czech Republic, Author

Supplementing the diet with Pediococcus pentosaceus enhances resistance to betanodavirus and ranavirus in groupers

Groupers in Asian aquaculture are often affected by nervous necrosis virus (NNV) and grouper iridovirus (GIV). This study evaluated the potential of Pediococcus pentosaceus strain 4012 (LAB4012) in protecting groupers from NNV and GIV. The results showed that supplementing the diet with LAB4012 for 1 to 4 weeks did not impact the growth rate of groupers. In the NNV and GIV challenge tests, the cumulative mortality in the LAB4012-fed groupers was lower compared to control group. After 4 weeks of LAB4012 supplementation, the gene expression levels of Mx increased in the head kidneys, while those of tumor necrosis factor (TNF)-α and C3 were elevated in the intestines. Additionally, phagocytic activity and respiratory burst in peripheral blood leukocytes were enhanced in the LAB4012-fed groupers. LAB4012 was found to successfully passed through the digestive tract and survived in the grouper intestines. Although the culture supernatant of LAB4012 did not trigger Mx gene expression in vitro, it was able to neutralize GIV, block the GIV receptors, and inhibit NNV replication. Therefore, LAB4012 shows promise as a potential application in grouper aquaculture for preventing NNV and GIV infection.

1. Wu, Yu-Chi, INSTITUTE OF FISHERIES SCIENCE, NATIONAL TAIWAN UNIVERSITY, Presenter
2. Chang, Chun-Kuei, INSTITUTE OF FISHERIES SCIENCE, NATIONAL TAIWAN UNIVERSITY, Author
3. Lin, Zhe-Li, INSTITUTE OF FISHERIES SCIENCE, NATIONAL TAIWAN UNIVERSITY, Author
4. Kai, Yu-Hsuan, INSTITUTE OF FISHERIES SCIENCE, NATIONAL TAIWAN UNIVERSITY, Author
5. Peng, Mu-Yun, DEPARTMENT OF LIFE SCIENCE, NATIONAL TAIWAN UNIVERSITY, Author

Probiotic Colonization and Antagonism of Moritella viscosa in Atlantic Salmon

Introduction

Winter ulcers, primarily caused by Moritella viscosa, are a leading bacterial disease affecting Atlantic salmon (Salmo salar), especially during colder seasons. With limited efficacy from existing vaccines and increasing restrictions on antibiotic use, probiotic bacteria have emerged as a promising alternative. Previous studies have documented a reduced prevalence of winter ulcers after administration of probiotic Aliivibrio spp. This study explores the colonization potential and antagonistic effects of Aliivibrio sp. strain Vl2 as a prophylactic measure against M. viscosa.

Methodology

Atlantic salmon were exposed to two Aliivibrio strains via bath immersion. Colonization was assessed through culture-based methods, qPCR, and immunohistochemistry (IHC) across various tissues over time. In vitro assays included co-cultivation of Aliivibrio Vl2 with M. viscosa and cytotoxicity testing using CHSE-214 cell lines. Transcriptomic analysis was performed to identify differential gene expression related to the probiotic-pathogen interaction.

Results

Probiotic Aliivibrio strains were recovered and vizualized in skin and distal intestinal samples up to nine months post-exposure. The probiotics were also detected within co-cultures with M. viscosa in winter ulcers. In co-culture, strain Vl2 significantly inhibited the growth of M. viscosa. Supernatant from Aliivibrio cultures reduced cell damage in CHSE cultures exposed to M. viscosa. Transcriptomic data revealed upregulation of genes involved in siderophore activity and synthesis of antibacterial compunds, supporting a mechanism of competitive exclusion and direct antagonism of the pathogen.

Conclusions

This study demonstrates that probiotic Aliivibrio spp. can colonize host tissues long-term and directly inhibit M. viscosa through multiple antagonistic mechanisms. These findings support the development of Aliivibrio-based probiotics as a preventative strategy to reduce bacterial disease incidence in salmon aquaculture and improve fish health management in a sustainable manner.

1. STEEN DOBLOUG, MARIUS, PREVIWO AS, Presenter
2. Foyn Nørstebø, Simen, Norwegian University of Life Sciences (NMBU), Author
3. Iakhno, Stanislav, Previwo AS, Author
4. Sørum, Henning, Norwegian University of Life Sciences (NMBU), Author

Antimicrobial peptide AP1 from microalgae as treatment for gilthead seabream (Sparus aurata) after hormonal disruption and bacterial challenge

Antimicrobial peptide AP1 from microalgae as treatment for gilthead seabream (Sparus aurata) after hormonal disruption and bacterial challenge

J.M. García-Beltrán^1,2, F. Méndez-Vivancos¹, M.A. Esteban², M. Arizcun¹, E. Chaves-Pozo^1*

1 COMU-IEO, CSIC, Spain.

2 University of Murcia, Spain

Email: elena.chaves@ieo.csic.es

Introduction

17α-ethynylestradiol (EE2) is a pharmacological compound present in water which acts as endocrine disrupting chemical (EDC) in fish affecting their immune response (Chaves-Pozo et al., 2018). For its part, antimicrobial peptides (AMPs) from microalgae could improve the immune system of fish due to their modulatory roles on fish immune system (Zhang et al., 2022). Therefore, in this work we evaluated the mitigation role of the peptide AP1 (an AMP from microalga Arthrospira platensis) in fish previously exposed to EE2 and challenged with Vibrio harveyi.

Methodology

Two groups of fish were established, fed with control diet (control group) or with diet containing 5 µg/g EE2 (EE2 group). Sampling were performed at 17 and 36 days of dietary intake. After 36 days both groups were challenged with V. harveyi and treated with AP1 1 day after being challenged. Control groups non-infected were also stablished. Survival of fish was recorded, as well as plasmatic and skin mucus vitellogenin (Vtg) levels (García-Hernández et al., 2020) and immune activities and stress status (García-Beltrán et al., 2024).

Results

The estrogenic alteration was evidenced by the higher level of Vtg in the plasma and skin mucus of fish treated with EE2. Those fish also showed growth, liver and head-kidney affected. In fact, most of the immune activities analysed were affected by EE2.

The fish treated with EE2 and infected with V. harveyi showed few immune activities affected, but failed to survive reaching 100% mortality after 9 days of infection.

Interestingly, the treatment with AP1 enhanced the immune system allowing a 90% survival rate through the regulation and activation of head-kidney leucocytes and higher levels of plasmatic hepcidin.

Conclusions

Our data demonstrated that the detection of Vtg in the skin mucus of fish is as a non-invasive method for detecting estrogenic effects and that AP1 is able to reduce the high mortality rates induced by EE2 exposure previous to a bacterial infection.

Acknowledgements

This research was supported by European Union NextGenerationEU/PRTR, MCIN/AEI10.13039/501100011033 and Fundación Séneca (ThinkInAzul program: PRTR-C17.I1) and by the Ministry of Universities through subsidies to public universities, Margarita Salas Grants, managed by the University of Murcia.

1. CHAVES-POZO, ELENA, COMU-IEO, CSIC, Presenter
2. García-Beltrán, José María, COMU-IEO, CSIC, Author
3. Méndez-Vivancos, Fernando, COMU-IEO, CSIC, Author
4. Esteban, M. Ángeles, University of Murcia, Author
5. Arizcun, Marta, COMU-IEO, CSIC, Author

ALGAE-ENRICHED DIETS IMPROVE THE SURVIVAL RATE UPON INFECTION IN JUVENILES OF GILTHEAD SEABREAM (SPARUS AURATA)

ALGAE-ENRICHED DIETS IMPROVE THE SURVIVAL RATE UPON INFECTION IN JUVENILES OF GILTHEAD SEABREAM (SPARUS AURATA)

Fernando Méndez-Vivancos¹, María Isabel Sáez², Francisco Javier Alarcón-López^{2, 3}, Tomás Francisco Martínez², Marta Arizcun Arizcun¹, Elena Chaves Pozo¹*

¹COMU-IEO, CSIC, Spain.

²Universidad de Almería, Spain.

³LifeBioencapsulation, Spain,

*elena.chaves@ieo.csic.es

Introduction

Infections caused by Vibrio harveyi and Photobacterium damselae subsp. piscicide represent a serious threat to marine aquaculture. As an alternative to antibiotic use, the application of microalgae containing immunostimulant compounds has emerged as an ecological strategy to enhance the innate immunity of fish and combat bacterial resistance.

Materials and methods

Two experimental trials were conducted at the Centro Oceanográfico de Murcia (COMU-IEO), CSIC using larvae and juveniles of gilthead seabream (Sparus aurata), fed during 49 or 94 days, respectively, with five different diets: a control diet (C) and four diets supplemented with algal biomass (either raw (R) or hydrolysed (H), at 5% and 10% inclusion levels: 5R, 5H, 10R or 10H, respectively). A mixture of microalgae was used for the larval diets, while in juveniles, the macroalga Alaria esculenta was also included. Immunological parameters such as peroxidase and bactericidal activities and immune-related gene expressions were evaluated, along with the survival rates upon infectious challenges with Photobacterium damselae subsp. piscicide or Vibrio harveyi respectively.

Results

The survival rates recorded in the 5R group of the larval trial were the highest, while being similar in the 10R and C groups. In contrast, in the juvenile’s trial, the 10H or 5R diets recorded the highest survival rates, being the 5H group which recorded similar survival rates than C.

In the larval trial, innate immune activities and the immune-related gene expression were modulated depending on the diet, but we could not correlate those effect with the survival rates. However, in the juvenile trial, an increase in peroxidase activity was observed across all experimental groups, with an additional rise in bactericidal activity detected specifically in the group fed with 10H diet.

Conclusions

The diets modulated some immune activities and genes in a way that clearly depend on the age of the specimens. Interestingly, in juveniles the 10H diet resulted in higher survival rates that correlated with higher peroxidase and bactericidal activities.

Acknowledgements

Thanks to The Spanish MCIN/AEI/10.13039/501100011033 (grants PID2021-122287OB-C21, PID2021-122287OB-C22 and EQC2019-006380-P) the last one to the Service of Experimental Diet for economic support and to the technical staff of the Aquaculture facilities of the COMU-IEO, CSIC

1. CHAVES-POZO, ELENA, COMU-IEO, CSIC, Presenter
2. Méndez-Vivancos, Fernando, COMU-IEO, CSIC, Author
3. Sáez, María Isabel, University of Almería, Author
4. Alarcón-López, Francisco Javier, University of Almería, Author
5. Martínez, Tomás Francisco, University of Almería, Author
6. Arizcun, Marta, COMU-IEO, CSIC, Author