Aquaculture Conditions Research Articles

Growth, immunomodulatory, histopathological, and antibacterial effects of phytobiotic-incorporated diets on Oreochromis niloticus in unchanged water

Phytobiotics are promising diet alternatives, yet their effectiveness in high-risk aquaculture conditions remains underexplored. Therefore, a 90-day feeding trial was conducted based on dietary supplementation of Nile tilapia, Oreochromis niloticus, with herbal extracts, namely, lemon balm [Melissa officinalis (MOE)], marjoram [Origanum majorana (OME)], and chamomile [Matricaria chamomilla (MCE)] with 0% water change. The treated groups were compared to groups untreated with herbs or control groups [positive control (PC; 0% water change) and negative control (NC; 20% water exchange per day]. Fish were cultured at stocking density (20 fish m-3: 1.8kg of biomass/m3). We conducted a physicochemical analysis of the water and the clinical responses, growth, and immune responses of the fish were evaluated. Furthermore, the herbal-supplemented fish were then challenged with a pathogenic Edwardseilla tarda strain and mortality was monitored. In the 1st and 2nd months, the water parameters were within the permissible limits. After that, a fatally low dissolved oxygen concentration and the highest levels of ammonia, nitrite, nitrate, and pH were recorded during the 3rd month. Blood and immune assays were conducted in the treated groups and control groups. The herbal-treated groups appeared healthy, but during the 3rd month, lethargy and decreased appetite were evident. Generally, the herbal-treated fish showed improved growth performance parameters, survival rates, and resistance against pathogenic bacteria E. tarda, particularly in the OME and MOE-treated groups compared to the positive control group. Finally, phytobiotic supplements were shown to improve fish stress tolerance and immune activation for a certain period under stressful conditions or unchanged water, based on the stocking density, dosages of herbs used, and the extent of deterioration of the water quality.

Influence of Different Lighting and Feeding Regimes on the Expression of the Fadsd5, Fadsd6, Elovl2, and Elovl5a Desaturase and Elongase Genes in the Liver of Juvenile Atlantic Salmon Salmo salar L. under Aquaculture Conditions

Influence of Different Lighting and Feeding Regimes on the Expression of the Fadsd5, Fadsd6, Elovl2, and Elovl5a Desaturase and Elongase Genes in the Liver of Juvenile Atlantic Salmon Salmo salar L. under Aquaculture Conditions

The impact of crowding stress on growth and intestinal integrity in largemouth bass (Micropterus salmoides): Insights into ER stress, autophagy and apoptosis

Crowding stress is a common abiotic stressor in intensive aquaculture that negatively impacts fish species, leading to growth depression. This study primarily explored the effects of crowding stress on the growth and intestinal integrity of largemouth bass (Micropterus salmoides). A 10-week feeding experiment was conducted with two groups: a control group (0.55 kg/m³) and a crowding stress group (1.10 kg/m³). The results showed that crowding stress significantly impaired fish growth and compromised intestinal integrity. To further elucidate the underlying mechanisms, we investigated the effects of crowding stress on endoplasmic reticulum (ER) stress, autophagy and apoptosis. Our findings revealed an increased proportion of terminal deoxynucleotidyl transferase (TdT) dUTP Nick-End Labeling (TUNEL)-positive cells and ER swelling in the intestines of stressed fish, along with a higher number of autophagosomes. Furthermore, there was a significant upregulation in the mRNA expression of genes related to ER stress, autophagy and apoptosis, including GRP78, eIF2α, IRE1, atg3, LC3-2, ulk1α, P62, and caspase-8. In conclusion, crowding stress negatively affects fish growth and intestinal integrity, potentially through the induction of apoptosis and autophagy associated with ER stress-mediated unfolded protein response (UPR). These findings provided critical insights into how intensive aquaculture disrupts intestinal integrity and inhibits growth in fish, offering a valuable reference for future research aimed at enhancing stress resistance in fish under intensive aquaculture conditions.

The effect of different levels of L-isoleucine in compound feeds on the growth of tilapia (Oreochromis niloticus)

Four diets were developed, including the control (main diet), which actually contained 34.00% crude protein, while the other three contained protein close to this value, taking into account the measurement error, and isoleucine in groups 2, 3 and 4, 4.9%, 8.51% and 12.12%, respectively. The study of the effect of L-isoleucine additives in compound feeds on the growth of tilapia (Oreochromis niloticus) showed that varying the concentration of this amino acid has a significant effect on fish growth rates. Adjusting dosages makes it possible to achieve more efficient use of feed in aquaculture conditions. It was found that when the amino acid isoleucine is introduced into the diet, feed conversion decreases by 0.64 points with an additional concentration of 1.42 g/kg of feed (4.9%), by 0.88 points with additional administration of isoleucine by 1.55 g/kg of feed (8.51%), by 0.76 points with an additional concentration of 1.68 g/kg of feed (12.12%). It was shown that the best group with the lowest feed conversion rate was the 3rd group, in which the amino acid isoleucine was introduced into the diet by 8.51% more than in other groups. The optimal level of isoleucine administration in tilapia feed is 1.55 g/kg of feed (8.51%). It was found that the ash content in the carcass of O. niloticus increased by 0.8%, fat — by 1% in muscles compared with the control.

EVALUATING GROWTH AND NUTRIENT COMPOSITION OF AFRICAN CATFISH UNDER DIFFERENT SALINITIES

An investigation was carried out to explore the effect of salinity on the growth and flesh quality of African catfish (Clarias gariepinus), a significant species in global aquaculture. Fifty juvenile catfish of weight 24.25±0.4g were collected from the Chenab River in Pakistan and acclimatized in controlled aquaculture conditions at different salinity levels NaCl (T1; 0, T2; 2, T3; 4; T4; 6, and T5; 8 ppt) over 60 days. Growth performance indicators, including final weights, weight gain, growth rate, and feed conversion ratio (FCR), were measured. The statistical result indicated that the fish in lower salinity environments (0-2 ppt) exhibited significant (p < 0.05) final weights, weight gain, and growth rates, with performance declining significantly as salinity increased. The best FCR 1.2±0.01 was indicated at 0 ppt, while the highest salinity (8 ppt) was revealed in the FCR 1.7±0.04. Proximate composition analysis indicated that crude protein and moisture content elevated with salinity while crude fat and ash content decreased. These results suggest that C. gariepinus thrives in slightly brackish conditions, with optimal growth at low salinity levels. However, higher salinities adversely impact physiological health and growth performance.

Unveiling the pathogenic and multidrug-resistant profiles of Vibrio alfacsensis: A potential identified threat in turbot (Scophthalmus maximus) aquaculture

Vibrio alfacsensis is traditionally seen as an environmental symbiont within its genus, with no detailedly documented pathogenicity in marine aquaculture to date. This study delves into the largely unexplored pathogenic potential and emerging antibiotic resistance of V. alfacsensis. The VA-1 strain, isolated from recirculating aquaculture system (RAS) effluent of cultured turbot (Scophthalmus maximus), underwent comprehensive analysis including biochemical identification, antibiotic susceptibility testing and reinfection trials. The results confirmed VA-1's pathogenicity and significant multiple antibiotic resistance. VA-1 could induce systemic infection in turbot, with symptoms like kidney enlargement, exhibiting virulence comparable to known Vibrio pathogens, with an LD50 around 2.36 × 106 CFU/fish. VA-1's remarkable resistance phenotype (14/22) suggested potential for genetic exchange and resistance factor acquisition in aquaculture environments. Phylogenetic analysis based on 16S rDNA sequences and whole-genome sequencing has firmly placed VA-1 within the V. alfacsensis clade, while genome-wide analysis highlights its similarity and diversity in relation to strains from across the globe. VA-1 contained numerous replicons, indicating the possibility for the spread of resistance and virulence genes. This study suggests V. alfacsensis may acquire and transfer pathogenic and resistant traits through horizontal gene transfer, a likelihood intensified by changing environmental and aquaculture conditions, highlighting the need for vigilant pathogen monitoring and new non-antibiotic treatments.

Expression of muscle-specific genes in atlantic salmon fingerlings (SALMO SALAR L.) in the conditions of aquaculture under the influence of different lighting and feeding regimes

Expression of muscle-specific genes in atlantic salmon fingerlings (SALMO SALAR L.) in the conditions of aquaculture under the influence of different lighting and feeding regimes

Carotenoid content in Ulva lactuca cultivated under aquaculture conditions and collected from intertidal beds in southeastern Brazil: biotechnological implications for biomass use and storage

Ulva lactuca is an edible green macroalga (Chlorophyta) that can be produced in cultivation systems; it is a natural source of high-value molecules. Ulva lactuca produces metabolites including carotenoids, which are pigments with antioxidant properties that are in high demand in the health and nutraceutical industries and improve the nutritional quality of U. lactuca biomass. We studied the carotenoid and chlorophyll content in U. lactuca thalli collected in 3 different environments in the state of Rio de Janeiro, Brazil: the intertidal beds of the urban beaches of Arpoador and Boa Viagem and a continental integrated multi-trophic aquaculture (IMTA) facility. Carotenoid conservation was evaluated during 1 week, 2 weeks, and 4 weeks of storage. We compared the molecules in fresh U. lactuca collected during the dry season (July 2018) and rainy season (February 2019). The content of carotenoids, such as β-carotene + zeaxanthin, lutein + antheraxanthin, violaxanthin, neoxanthin, and their derivatives (aurochrome and auroxanthin), were analyzed in 100% acetone extracts by ultraviolet visible (UV/vis) spectrophotometry and monitored by thin layer chromatography (TLC) and proton nuclear magnetic resonance (1H-NMR). The extracts of dried U. lactuca produced in the IMTA facility presented higher pigment yields than the dried biomass collected from intertidal beds. Over 4 weeks of storage, carotenoids were well conserved in U. lactuca produced in the IMTA facility, in contrast to what was observed in U. lactuca collected from the intertidal beds, which showed carotenoid losses. In addition, we observed differences in carotenoid content between the dry and rainy seasons in U. lactuca collected from Boa Viagem Beach. However, the U. lactuca collected from Arpoador Beach or produced by the IMTA facility only exhibited significant differences in chlorophyll content. We conclude that U. lactuca produced by the IMTA facility constitutes a potential source of pigments such as β-carotene, lutein, and violaxanthin.

Comparison of ovarian mRNA expression levels in wild and hatchery-produced greater amberjack Seriola dumerili

The greater amberjack Seriola dumerili is a promising candidate for aquaculture production. This study compares the ovary transcriptome of greater amberjack sampled in the wild (WILD) with hatchery-produced breeders reared in aquaculture sea cages in the Mediterranean Sea. Among the seven sampled cultured fish, three were classified as reproductively dysfunctional (DysF group), while four showed no signs of reproductive alteration (NormalF group). The DysF fish showed 1,166 differentially expressed genes (DEGs) compared to WILD females, and 755 DEGs compared to the NormalF. According to gene ontology (GO) analysis, DysF females exhibited enrichment of genes belonging to the biological categories classified as Secreted, ECM-receptor interaction, and Focal adhesion. Protein–protein interaction analysis revealed proteins involved in the biological categories of ECM-receptor interaction, Enzyme-linked receptor protein signaling, Wnt signal transduction pathways, and Ovulation cycle. KEGG pathway analysis showed DEGs involved in 111 pathways, including Neuroactive ligand-receptor interaction, Steroid hormone biosynthesis, Cell cycle, Oocyte meiosis, Necroptosis, Ferroptosis, Apoptosis, Autophagy, Progesterone-mediated oocyte maturation, Endocytosis and Phagosome, as well as Hedgehog, Apelin, PPAR, Notch, and GnRH signalling pathways. Additionally, DysF females exhibited factors encoded by upregulated genes associated with hypogonadism and polycystic ovary syndrome in mammals. This study -which is part of a broader research effort examining the transcriptome of the entire reproductive axis in greater amberjack of both sexes-, enhances our comprehension of the mechanisms underlying the appearance of reproductive dysfunctions when fish are reared under aquaculture conditions.

A method for counting fish based on improved YOLOv8

In industrial aquaculture, accurately counting fish in real-time is crucial for optimizing feeding strategies, preventing disease, and managing water quality. Current methods utilizing sensors, acoustics, machine learning, and density map regression face challenges such as high costs, invasiveness, and computational complexity. To address these limitations, we propose the YOLOv8n-MEMAGD method for accurate real-time fish counting. This method enhances YOLOv8 by incorporating the GELU activation function, MPDIoU for localization loss, and the C2f-FAM and C2f-MSCA modules into the backbone network. Additionally, the neck network is redesigned with a gather-and-distribution mechanism. Experimental results under land-based industrial aquaculture conditions demonstrate that YOLOv8n-MEMAGD achieved a mean absolute error (MAE) of 2.28 and a root mean square error (RMSE) of 2.84, even in challenging conditions such as fish overlap, aggregation, and background confounding. Compared to YOLOv8n, the proposed method increased average precision (AP50) for fish detection by 6.2 %, and significantly reduced MAE and RMSE by 61.4 % and 65.2 %, respectively, compared to CSRNet. Additionally, the method achieved a frame rate of 61 frames per second (FPS) when the number of fish ranged from 79 to 91, representing a 390.4 % increase over CSRNet. By comparing heatmaps, the proposed method demonstrates more effective detection of fish edge contours than current advanced algorithms. In conclusion, the proposed method shows promise for application in aquacultural scenarios with higher turbidity and larger number of fish.

The dynamics of catching aquatic bioresources in the south of Ukraine: Analysis, challenges and prospects for their solution in the context of sustainable development

Given the significance of fish farming as a promising sector of Ukraine’s agriculture, and the Mykolaiv, Odesa, and Kherson regions are characterised by a significant number of natural and artificial water bodies, the study of aquatic bioresource catching indicators in the south is both important and timely. The research aimed to determine trends in aquatic bioresource catching in southern Ukraine during the period 2018-2023 and to analyse the factors influencing the extraction of aquatic bioresources. This article presents overall catch statistics, as well as catch data for inland waters of the south and aquaculture conditions over the past six years. It has been established that the catch of aquatic biological resources in southern Ukraine has been declining each year from 2018 to 2023. The negative trends in aquatic bioresource catching, both in aquaculture and natural water bodies, are linked to several factors. In particular, the decline in catches has been influenced by: COVID-19; the unstable military and political situation in Ukraine, associated with Russian military aggression; outdated material and technical base of fishing enterprises; lack of government subsidies and foreign investment in the sector; imperfections in the systems of control and regulation of the extraction of aquatic bioresources; and irrational use of the bioproductive potential of water bodies in southern Ukraine. Based on a scientific analysis of the dynamics of aquatic bioresource extraction in southern Ukraine and the identification of key factors contributing to the decline in catches, a set of measures has been developed to positively impact the fishing industry. These measures include: attracting foreign investment in fish farming; improving the quality of monitoring, regulation, and control over aquatic bioresource catching at local, regional, and state levels; restoring critical fish farming infrastructure damaged by Russian aggression; ensuring sustainable fisheries management; and introducing EU best practices into Ukrainian fish farming. The scientific results obtained from this research can be used in practice to ensure the sustainable development of fisheries in southern Ukraine

Chemical composition of muscle tissue of fish reared in the aquaculture of South Vietnam

To study the chemical composition of four species of valuable fish reared in aquaculture conditions in South Vietnam.Individuals of Channa striata, Channa gachua, Oreochromis niloticus, a hybrid of Clarias gariepinus and Clarias macrocephalus were purchased in markets from farmers of cage farms and directly in the farms of Khanh Hoa province. The fish were measured, weighed, and then muscle tissue was dissected for chemical analysis. The water content in the tissue was determined by a two‐stage method for determining moisture, while lipids were determined by the fat‐free residue method in a Soxhlet apparatus. The amount of protein was obtained according to the principle of the Kjeldahl method, using a semi‐automatic distillation unit UDK 139 (Velp Scientifica, Italy, 2011); minerals were determined by the gravimetric method, and carbohydrates – by calculation. The index of physiological state was calculated according to the standard method.Hybrid catfish muscles are characterised as having the greatest nutritional value. In terms of lipid content, the individuals studied belonged to fish with a low fat content, Channa striata, which belongs to the category of lean fish. A high index of physiological state in Oreochromis niloticus was found to be associated with increased water content in muscle tissue. No significant differences were found between the biochemical parameters in the muscles of fish with an increase in body size, and only in Channa striata did the proportion of minerals increase. The data obtained can be used in the organisation of rational feeding and maintenance of aquacultural species.

Genotoxic effects in blood cells of sturger (Acipenseridae) grown in conditions of cage farming of the Volga delta, Russia

The purpose of this work was to assess the degree of genotoxic influence of the habitat on individuals of Russian sturgeon and sterlet raised in cage farming conditions in the Volga delta, using micronucleus and DNA comet tests.The blood of the individual Russian sturgeon and sterlet was shaved off during their lifetime. A comet DNA test was performed using the alkaline method. The number of erythrocytes with micronuclei was determined microscopically. To assess the physiological state of sturgeons, conventional hematological and biochemical methods were used.In the samples of fish blood smears studied, the average proportion of erythrocytes with micronuclei was 3.20 ± 1.24 ‰ in Russian sturgeon and 5.25 ± 1.18 ‰ in sterlet. The proportion of DNA in the comet tail in erythrocytes of Russian sturgeon was 3,99 %, and in sterlet 6, 48 %. The values of tail moment and Olivet moment were also lower in Russian sturgeon. Among sterlet erythrocytes, a more heterogeneous pattern of DNA damage can be noted. The length of the comet tail in starlet individuals turned out to be lower than in Russian sturgeon: apparently, larger fragments of these molecules were formed when the DNA of starlet erythrocytes was damaged. The physiological state of sterlet individuals can be characterised as normal, and that of the Russian sturgeon as satisfactory, due to the deviations identified in the values of some hematological and biochemical blood parameters.Having studied the influence of the environment on individual sturgeon kept in cage aquaculture conditions in the Volga delta using micronuclear and DNA comet tests, we can conclude that there was no acute genotoxic effect at the time of the study.

Increase of resistance and improvement of adaptation and compensatory mechanisms of the body of juvenile fish under conditions of multitrophic aquaculture

Increase of resistance and improvement of adaptation and compensatory mechanisms of the body of juvenile fish under conditions of multitrophic aquaculture

Surveying the welfare of farmed fish species on a global scale through the fair-fish database.

Fish welfare is a critical issue that needs to be addressed by the rapidly growing aquaculture industry. Scientific knowledge regarding the natural behaviors of species and the conditions in which they are kept in farms is essential for improving their welfare in aquaculture. To provide a consistent overview of the welfare of farmed fish, the organization fair-fish has created the online platform fair-fish database, which gathers ethological knowledge categorized into profiles of farmed aquatic species. The WelfareChecks on this platform are profiles based on criteria that are rated based on the likelihood and potential of the species to experience a high level of welfare in aquaculture systems, together with the certainty about the findings. A score (WelfareScore) is calculated from these ratings, serving as a reference to identify knowledge gaps, assess welfare, and suggest ways to improve it. Here, we performed an in-depth analysis of the species with WelfareChecks already published in the fair-fish database based on their respective WelfareScores. In general, although just a small percentage of farmed aquatic species (~5%) have at least a 20% chance of experiencing a good level of welfare under minimal aquaculture conditions, 60% of them have at least some potential to achieve good welfare under high-standard conditions, with more than a third of the species (~37%) having at least a 20% potential. Despite that, several species exhibit a very high frequency of low chances and potential for experiencing good welfare levels under aquaculture conditions, besides a low degree of certainty based on literature reviews. Furthermore, many others show a very frequent occurrence of unclear or nonexistent knowledge in their profiles. The current welfare state is therefore poor for the majority of farmed aquatic species; yet, there is considerable potential for improvement. However, many species are very unlikely to achieve good welfare, even under high-standard conditions. Importantly, large knowledge gaps remain for an accurate assessment of the welfare of several farmed species.

Thermal modulation of energy allocation during sex determination in the European sea bass (Dicentrarchus labrax)

Water temperature governs physiological functions such as growth, energy allocation, and sex determination in ectothermic species. The European sea bass (Dicentrarchus labrax) is a major species in European aquaculture, exhibiting early dimorphic growth favoring females. The species has a polygenic sex determination system that interacts with water temperature to determine an individual’s sex, with two periods during development that are sensitive to temperature. The current study investigated the influence of water temperature on energy allocation and sex-biased genes during sex determination and differentiation periods. RNA-Sequencing and qPCR analyses were conducted in two separate experiments, of either constant water temperatures typical of aquaculture conditions or natural seasonal thermal regimes, respectively. We focused on eight key genes associated with energy allocation, growth regulation, and sex determination and differentiation. In Experiment 1, cold and warm temperature treatments favored female and male proportions, respectively. The RNA-seq analysis highlighted sex-dependent energy allocation transcripts, with higher levels of nucb1 and pomc1 in future females, and increased levels of egfra and spry1 in future males. In Experiment 2, a warm thermal regime favored females, while a cold regime favored males. qPCR analysis in Experiment 2 revealed that ghrelin and nucb1 were down-regulated by warm temperatures. A significant sex-temperature interaction was observed for pank1a with higher and lower expression for males in the cold and warm regimes respectively, compared to females. Notably, spry1 displayed increased expression in future males at the all-fins stage and in males undergoing molecular sex differentiation in both experimental conditions, indicating that it provides a novel, robust, and consistent marker for masculinization. Overall, our findings emphasize the complex interplay of genes involved in feeding, energy allocation, growth, and sex determination in response to temperature variations in the European sea bass.

Effects of four types of natural bait on water quality, feeding, growth, and antioxidant enzyme activity of Monopterus albus in a recirculating aquaculture system

Monopterus albus is one of China’s renowned and superior aquaculture species, with its seedlings mainly sourced from wild capture. One of the bottlenecks in M. albus aquaculture is the high mortality rate and low feeding initiation rate from stocking wild fry to the initiation of feeding. In production, trash fish is commonly used to wean M. albus juveniles onto feeding. In this study, we introduced three other natural feeds, earthworms (EW), yellow mealworms (YMW), and fly maggots (FM), with frozen trash fish (TF) serving as the control group, to evaluate the effects of these four natural feeds on the survival rate, feeding initiation, antioxidant enzymes activity, and body composition of M. albus juveniles under recirculating water aquaculture conditions. The experiment comprised four treatments, each with three replicates. Each replicate consisted of stocking 150 M. albus juveniles weighing 10.02 ± 0.89 g in size, raised for 5 weeks. The survival rate of the YMW group was 73.33%–85.33%, which was significantly higher than that of the other three bait groups (p < 0.05). The four bait groups showed no significant differences in final body weight and specific growth rate (SGR) (p > 0.05). The EW group showed the highest final body weight, with an average SGR of 2.73, whereas the YMW group had an average SGR of 1.87. The average daily feeding amount was significantly higher in EW and YMW groups than in the other two groups (p < 0.05). The percentage of feeding amount to fish weight in the EW group reached 7.3% in the fifth week. After 5 weeks of cultivation, NO2−-N content was significantly higher in the waters of the TF and EW groups than in the waters of the FM and YMW groups (p < 0.05), there was no significant difference in TAN content among the treatment groups (p > 0.05). Liver malondialdehyde content was significantly higher in the TF group than in the other bait groups (p < 0.05). GSH-Px activity was significantly higher in the EW group than in the FM group and YMW group. No significant differences in SOD and CAT activity and T-AOC were observed among the bait groups (p > 0.05). The increase in crude protein content was significantly higher in the TF group than in the FM group, but the increase in crude ash content was significantly lower in the TFgroup. In conclusion, Tenebrio molitor could potentially serve as one of the alternative feeds during the initial stages of M. albus juveniles stocking.

Aquaculture Monitoring and Control System Based On IOT

- This project offers a comprehensive solution for monitoring and regulating aquaculture conditions using cutting-edge Internet of Things (IoT) technology. By leveraging ESP8266 NodeMCU and Arduino UNO, alongside a range of sensors including the DS18B20 waterproof temperature sensor, water level sensor, and turbidity sensor, it ensures real-time monitoring of vital parameters in aquatic environments. Precise control of water circulation and management is made possible through the integration of motor drivers with submersible pumps. The Blynk App serves as the user-friendly control interface, granting remote access and management of water pumps. Meanwhile, sensor data is continuously collected and displayed on ThingSpeak, offering consumers valuable insights into the current state of their aquaculture setup. This project harnesses IoT technology to enhance aquaculture management efficiency and productivity, while also ensuring optimal environmental conditions for aquatic life. Its modular design enables scalability and customization, catering to various aquaculture configurations and settings. Key Words: Arduino UNO, Sensors, Motor Driver, Wifi Module, ThingSpeak, IOT, Aquaculture, Blynk App.

Nutritional value of clariid catfish in the conditions of aquaculture in Ukraine

Nutritional value of clariid catfish in the conditions of aquaculture in Ukraine

The effects of Pediococcus acidilactici MA18/5M on growth performance, gut integrity, and immune response using in vitro and in vivo Pacific salmonid models.

Microbial management is central to aquaculture's efficiency. Pediococcus acidilactici MA18/5M has shown promising results promoting growth, modulation of the immune response, and disease resistance in many fishes. However, the mechanisms through which this strain confers health benefits in fish are poorly understood, particularly in Pacific salmonid models. Briefly, the aims of this study were to i) assess the protective effects of P. acidilactici MA18/5M by examining gut barrier function and the expression of tight junction (TJ) and immune genes in vitro and in vivo, and ii) to determine the protective effects of this strain against a common saltwater pathogen, Vibrio anguillarum J382. An in vitro model of the salmonid gut was employed utilizing the cell line RTgutGC. Barrier formation and integrity assessed by TEER measurements in RTgutGC, showed a significant decrease in resistance in cells exposed only to V. anguillarum J382 for 24 h, but pre-treatment with P. acidilactici MA18/5M for 48 h mitigated these effects. While P. acidilactici MA18/5M did not significantly upregulate tight junction and immune molecules, pre-treatment with this strain protected against pathogen-induced insults to the gut barrier. In particular, the expression of ocldn was significantly induced by V. anguillarum J382, suggesting that this molecule might play a role in the host response against this pathogen. To corroborate these observations in live fish, the effects of P. acidilactici MA18/5M was evaluated in Chinook salmon reared in real aquaculture conditions. Supplementation with P. acidilactici MA18/5M had no effect on Chinook salmon growth parameters after 10 weeks. Interestingly, histopathological results did not show alterations associated with P. acidilactici MA18/5M supplementation, indicating that this strain is safe to be used in the industry. Finally, the expression pattern of transcripts encoding TJ and immune genes in all the treatments suggest that variation in expression is more likely to be due to developmental processes rather than P. acidilactici MA18/5M supplementation. Overall, our results showed that P. acidilactici MA18/5M is a safe strain for use in fish production, however, to assess the effects on growth and immune response previously observed in other salmonid species, an assessment in adult fish is needed.