The rapid intensification of global aquaculture, particularly the widespread application of recirculating aquaculture systems (RAS), has substantially improved aquatic product yield [...]
Global inland fisheries depend on large reservoirs, yet many assessments assume spatial homogeneity despite complex embayed morphometry. We tested whether khor-scale structure within Lake Nasser, Egypt, explains variation in two commercially important catfishes. Six distinct khors spanning the north–south axis (Ghazal, Sheniara, Garf Hussein, Amada, Toshka, and Hamedo) were sampled with standardized effort (72 net-nights; 12 per khor, 3 representative areas ≥ 500 m apart × 4 campaigns, March–June 2021), yielding 398 fish (268 Chrysichthysauratus, 130 C. rueppelli). Abundance was expressed as standardized CPUE (fish·net-night−1). C. auratus CPUE ranged from 2.83 (Ghazal) to 5.92 (Garf Hussein), while C. rueppelli CPUE was relatively uniform (1.50–1.92). C. auratus attained the largest TL in Ghazal (25.51 ± 2.9 cm) and the highest condition K in Garf Hussein (1.46 ± 0.18). C. rueppelli attained the greatest TL and weight in southern khors, especially Hamedo (23.3 ± 2.33 cm, 146.7 ± 30.5 g), while its highest condition was in Toshka (1.30 ± 0.15). Sex ratio was significantly female-biased for C. auratus (92 M:176 F, 1:1.91, p < 0.001) but not for C. rueppelli (55 M:75 F, 1:1.36, p = 0.079). Results show embayment-scale CPUE and condition, not whole-lake means, capture key population patterns, improving precision of mega-reservoir fisheries management.
This study compared conventional aquaponics (AP), biofloc-based aquaponics (FLOCponics, FP), and hydroponics (HP) in terms of juvenile eel (Anguilla japonica) growth, ‘Caipira’ lettuce (Lactuca sativa) productivity, and water-quality characteristics. The AP and FP treatments each comprised three replicate fish tank–plant cultivation systems stocked with 119 eels per tank, whereas HP was included as a control for plant production. Eels reared in FP exhibited a higher estimated final biomass and specific growth rate and a lower feed conversion ratio than those reared in AP. The total and shoot biomass of lettuce were higher in FP than in AP and were comparable to those obtained in HP.
This study investigates the length–weight relationship, growth patterns, and population structure of Prochilodus nigricans in a tropical river environment, providing biometric information relevant to ecological studies, fisheries assessment, and conservation planning. A total of 139 individuals were sampled across rainy and dry seasons, and biometric variables (BD—Body Depth, TL—Total Length, SL—Standard Length, TW—Total Weight, and GW—Gonad Weight) were compared using descriptive statistics and regression analyses. Significant differences in biometric parameters were observed between seasons and sexes. Among the sampled individuals, body depth, standard length, total length, and total weight were significantly higher during the rainy season for both sexes; however, these differences should be interpreted with caution because different gill-net mesh sizes were used between hydrological periods. Gonad weight and gonadosomatic index (GSI) differed significantly between males and females in both seasons. A significant overall effect of season was detected for gonad weight, although pairwise seasonal differences were observed only in males, whereas no significant seasonal effect was detected for GSI. Length–weight relationships indicated isometric growth in both sexes. These results provide baseline biometric information useful for future ecological studies and complementary fisheries assessments of P. nigricans in the Tocantins–Araguaia Basin.
Understanding niche differentiation and interspecific coexistence patterns of macrobenthos provides critical references for ecological assessment of bivalve aquaculture. Seasonal field surveys (Autumn 2023–Summer 2024) across 12 sampling sites were conducted in an intensive Meretrix meretrix tidal flat farm in Rudong, Jiangsu. Synchronous water depth, sediment grain size and total organic carbon (TOC), and salinity were measured at each station to characterize habitat gradients; no unfarmed reference tidal flats were included, so all community patterns only reflect within-farm variation. The study area has sustained 10-year continuous bottom culture with baseline juvenile stocking density of 250 ind./m2 and twice-yearly manual harvesting. A total of 58 macrobenthic taxa were identified, and 13 dominant species were screened with a dominance index threshold Y > 0.02. All abundance data were fourth-root-transformed before Bray–Curtis community analysis to reduce bias of hyper-abundant taxa. Standardized Shannon niche breadth (0–1 normalized, r = 48 site–season composite units) and permutation-tested (999 replicates) Pianka niche overlap/similarity coefficients were calculated to quantify resource utilization similarity. Niche breadth ranged from 0.018 to 0.971, with farmed M. meretrix showing the maximum value, indicating broader seasonal resource adaptation. High niche overlap (>0.50) was detected between M. meretrix and four wild dominant species (Nephtys californiensis, Moerella iridescens, Lingula anatina, Umbonium thomasi). Notably, niche metrics derived solely from spatial abundance data cannot directly confirm interspecific competition or trophic segregation; the stable coexistence observed in our assemblage is tentatively hypothesized to be driven by vertical sediment partitioning and divergent feeding guilds based on published functional studies, without direct in situ trophic or stratified sediment evidence from this work. Hierarchical UPGMA clustering (0.35 Bray–Curtis distance threshold) and corrected NMDS ordination (48 site–season units, dominant-species fitted vectors) illustrated distinct functional groups. Based on the observed niche convergence among filter-feeding bivalves under local farming conditions, the range of 230–280 ind./m2 is presented as an observational reference. Controlled manipulative experiments with gradient stocking densities are needed to test whether this range can balance aquaculture yield and benthic biodiversity.
To evaluate the economic and ecological potential of black soldier fly larvae (BSFL) slurry as a fishmeal alternative, 270 juvenile Pangasius (initial body weight: 7.20 ± 0.07 g) were acclimated for two weeks and randomly allocated to three dietary treatments (T0, T1, T2), with three biological replicates per treatment. The feeding trial lasted six weeks (42 days). Fish in T0 were fed the basal diet, while T1 and T2 diets replaced 50% and 100% of fishmeal with BSFL on an isonitrogenous basis, respectively. At trial termination, whole-body proximate composition, muscle texture, and intestinal microbiota were analyzed. BSFL inclusion at 50–100% fishmeal replacement did not compromise growth performance. Moisture and ash content did not differ among treatments (p > 0.05), whereas BSFL supplementation significantly altered muscle texture, reducing hardness and resilience while increasing springiness, chewiness, cohesiveness, and adhesiveness. Both 50% and 100% BSFL replacement enhanced hepatic antioxidant capacity, evidenced by significantly higher superoxide dismutase (SOD) activity (p < 0.05). BSFL also modulated intestinal microbiota and enhanced community evenness, though without significant intergroup differences in bacterial abundance (p > 0.05). This study demonstrated that BSFL could replace 50–100% of fishmeal in diets for juvenile Pangasius, maintaining growth performance while modifying nutritional profiles, muscle texture, hepatic antioxidant status, and intestinal microbiota. Nevertheless, 100% fishmeal replacement triggered distinct shifts in intestinal microbial composition despite satisfactory growth, and the 50% substitution level was, therefore, recommended as a safe proportion for practical aquafeeds.
Catch-and-release (C&R) fishing has become a common practice. Anatomical hooking location (AHL) can be crucial to fish survival. The length of the slack line connecting the hook to the rest of the rig (leader) can affect both the anatomical hooking location and catch efficiency. In this study, we set out to determine whether such a scenario would occur. A total of 2826 fish representing nine species were captured during the study. The shorter leader (15 cm) yielded 1462 fish (51.7%), whereas 1364 fish (48.3%) were captured using the 40 cm leader. Mean catch per unit effort (CPUE) was higher for the shorter leader (44.3 fish h−1) than for the longer leader (41.3 fish h−1). Fish were most frequently hooked in superficial, non-critical anatomical hooking locations within the mouth (upper and lower jaw and mouth corners). Safe hook placements accounted for 88.0% of captures with the 15 cm leader and 78.7% with the 40 cm leader. The research supported our hypothesis and predictions: a shorter leader is safer for fish and less likely to cause deep hooking in critical anatomical locations. On the other hand, shallower hooking was associated with higher catch efficiency. Our findings can help anglers design terminal tackle appropriately.
This study investigated the effects of glycerol monolaurate (GML) on the growth performance, physiological efficacy, intestinal structure, and microbiota of hybrid juvenile ♀ Epinephelus fuscoguttatus × ♂ E. lanceolatus. A total of 594 groupers were administered diets supplemented with 0, 2, 4, 6, 8, or 10 g/kg of GML over an 80-day period. The findings indicated that the group receiving 4 g/kg GML supplementation demonstrated significantly enhanced growth performance, as evidenced by increased weight gain, specific growth rate, and a reduced feed conversion ratio compared with the control and other experimental groups. This growth enhancement was associated with elevated catalase and glutathione levels, suggesting improved antioxidant capacity that may contribute to enhanced immune function. Furthermore, fish in the 4 g/kg group exhibited increased digestive enzyme activity and significantly improved intestinal morphology, characterized by thicker muscular layers and a greater fold width and height. Furthermore, compared with the control group, GML supplementation elevated the relative abundance of Proteobacteria while reducing that of Firmicutes at the phylum level. At the genus level, GML markedly suppressed the relative abundance of Mycoplasma and Vibrio. These compositional alterations are potentially linked to improved energy acquisition and a decreased risk of pathogenic infections. Collectively, these results reveal that GML acts as a promising functional feed additive to boost growth performance, optimize digestive capacity, and sustain intestinal structural integrity in hybrid grouper. Based on these results, the optimal GML supplementation dose was determined to be 4 g/kg, providing valuable insights into the role of GML in aquaculture practices for hybrid grouper.
The yellow clam, Amarilladesma mactroides, is an abundant component of the intertidal infauna of the southwestern Atlantic Ocean and an important source of food and income for local communities. In recent years, this species has been increasingly affected by anthropogenic and environmental pressures, contributing to the decline and collapse of several populations. In this study, we characterized the reproductive cycle of A. mactroides in the southernmost region of Brazil using standard approaches, including gonadal histology and biometric parameters, complemented by analyses of proximal composition and fatty acid profiles. Monthly samples of ≥100 clams were collected from October 2021 to September 2022. The results revealed two distinct reproductive peaks: a major peak from October to December (austral spring–summer) and a less pronounced peak from May to July (autumn–winter). Although gonadal histology, particularly oocyte diameter, provided the primary evidence for defining these reproductive peaks, the condition index and concentrations of total lipids and n-3 polyunsaturated fatty acids (n-3 PUFA) also proved useful indicators of reproductive activity. These findings provide new insights into the reproductive dynamics of A. mactroides in southern Brazil and may contribute to the development of strategies for the sustainable management, conservation and aquaculture of this ecologically and socioeconomically important bivalve.
The development of first-feeding protocols is a critical step in the domestication of native fish species for aquaculture. This study aimed to evaluate the first-feeding management of Pseudopimelodus atricaudus, a Neotropical catfish with aquaculture potential, using four prey types: Artemia nauplii (AN), decapsulated Artemia cysts (DC), wild zooplankton smaller than 400 µm (WZ < 400), and larger than 400 µm (WZ > 400). Larvae of P. atricaudus begin exogenous feeding at 30 h post-hatch (1.5 ± 0.02 mg and 5.2 ± 0.01 mm) and have a maximum mouth width of 611.4 ± 11.7 µm. Larvae fed WZ > 400 µm showed significantly higher growth (13.7 ± 0.2 mm, 94.6 ± 1.8 mg) and final survival (91.2 ± 2.2%) compared to the other treatments (p < 0.05), as well as a greater intestinal fold height (129.8 ± 8.4 µm, p < 0.05). No significant differences in hypoxia stress resistance were detected among treatments (p > 0.05). This study demonstrated that WZ > 400 µm is an appropriate prey for managing the first feeding of P. atricaudus.
Large yellow croaker (Larimichthys crocea) is an economically important marine fish, yet rapid and non-destructive discrimination between sea-caught and farmed collection-source groups remains challenging. This study developed a fish-level analytical workflow integrating YOLO11n-seg instance segmentation with visible–near-infrared hyperspectral imaging to extract relative reflectance ratios from six anatomical regions. The analytical cohort comprised 258 unique fish, including 171 sea-caught and 87 farmed individuals. Source categories were assigned according to the original capture or cage-culture collection channels. Fish identity was used as the grouping unit in five-fold internal cross-validation, and classification performance was evaluated based on out-of-fold fish-level predictions. Logistic-regression models achieved AUC values ranging from 0.985 to 1.000 across the six individual anatomical regions. The combined six-region model achieved an accuracy of 0.996 (95% CI, 0.988–1.000) and an AUC of 1.000 (95% CI, 1.000–1.000) within the present cohort. For anatomical-region segmentation, the 20-image validation set contained 140 annotated instances. Bounding-box precision, recall, mAP@0.5, and mAP@0.5–0.95 were 0.976, 0.983, 0.981, and 0.700, respectively, while the corresponding mask metrics were 0.969, 0.976, 0.972, and 0.669. These results indicate that region-specific hyperspectral information can support highly accurate internal discrimination between the two collection-source groups and provide an interpretable basis for characterizing source-associated spectral differences. However, the source labels were not independently verified, potentially influential covariates were incompletely recorded, and no independent external cohort was available. Therefore, the present findings should be interpreted as internally validated collection-source discrimination rather than verified provenance authentication or evidence of external generalizability.
Photobacterium damselae subsp. damselae (PDD), a marine fish pathogen, has an unclear contribution of tonB genes to iron acquisition and pathogenicity. ΔtonB1-PDD and ΔtonB2-PDD mutants as well as their complemented strains were generated via homologous recombination from the virulent strain PDD1605. Growth was evaluated by monitoring OD600 with viable-count calibration, intracellular iron was measured using a colorimetric assay, biofilm was detected by crystal violet staining, transcription was analyzed through qRT-PCR, and pathogenicity was assessed via an 8-day intramuscular challenge in black rockfish (Sebastes schlegelii). Under iron limitation induced by 100 μM 2,2′-dipyridyl, the maximum density decreased from 4.51 × 108 CFU/mL in wild-type (WT-PDD) to 4.00 × 108 and 3.64 × 108 CFU/mL in ΔtonB1-PDD and ΔtonB2-PDD respectively, and was largely restored after complementation. The intracellular iron content declined from 3.75 × 10−4 ± 4.00 × 10−6 nmol/106 cells in WT-PDD to 3.13 × 10−4 ± 1.05 × 10−5 nmol/106 cells in ΔtonB1-PDD and 2.55 × 10−4 ± 2.00 × 10−5 nmol/106 cells in ΔtonB2-PDD. Compared with WT-PDD, biofilm formation was reduced by 22.1% in ΔtonB1-PDD and by 24.8% in ΔtonB2-PDD. Deletion of tonB2 induced mild yet statistically significant transcriptional alterations in multiple iron acquisition and virulence-related genes, while colony morphology, swarming motility, hemolysis, phospholipase activity, biochemical traits, and antimicrobial susceptibility remained unchanged. In the high-dose challenge assay, WT-PDD caused 100% mortality within 2 days, whereas ΔtonB1-PDD and ΔtonB2-PDD caused 17/20 and 18/20 deaths respectively; all infected groups reached 100% mortality by day 3. In the low-dose challenge assay, WT-PDD, ΔtonB1-PDD, and ΔtonB2-PDD caused 12/20, 12/20, and 13/20 deaths by day 2, with cumulative mortalities reaching 80%, 70%, and 80% by day 8, respectively. Kaplan–Meier analysis detected no significant differences among the survival curves at either challenge dose. These findings suggest that tonB1 and tonB2 play roles in iron acquisition, low-iron adaptation, and biofilm formation, with tonB2 deletion exerting greater effects on growth and intracellular iron accumulation under iron-limited conditions.
Culvert construction at stream crossing sites can lead to zones of high-velocity water flow which can disrupt the dispersal and connectivity of species of greatest conservation need (SGCN) in Texas. To help inform effective culvert design, the swimming performance of the following seven fish species has been measured, the first three of which are SGCN themselves, and the last four serve as hosts for glochidia of SGCN mussels (mussel genera indicated in parentheses): Colorado Roundnose Minnow, Texas Shiner, Headwater Catfish, Largemouth Bass (host for Lampsilis spp.), Green Sunfish (host for Lampsilis spp.), Channel Catfish (host for Cyclonaias spp.) and Blacktail Shiner (host for Fusconaia spp.). The primary objective was to measure the critical swimming speeds (Ucrit) under a range of relevant temperatures (15, 22.5, and 30 °C) to be used in site-specific calculations of culvert water velocities (Vf). A secondary objective was to collect additional physiological endpoints of relevance to overall swimming performance, including maximum burst swimming speed (Umax), metabolic rate measurements (i.e., standard (SMR), maximum (MMR) and aerobic scope (AS)) and calculations of cost of transport (COT) and optimal swimming speed (Uopt). As expected, Ucrit tended to increase with increasing temperature for several species with metabolic rate measurements following congruent trends, whereas Umax exhibited thermal independence for all species.
Using a three-factor orthogonal design, we investigated the transcriptomic and histological responses of triploid rainbow trout (Oncorhynchus mykiss) gills across three salinities (10, 20, and 30 ppt) over 60 days, with temperature and body size as background conditions. Results showed that 20 ppt was associated with extensive transcriptional reprogramming, with 3333 differentially expressed transcripts (DETs), whereas 30 ppt induced only 120 DETs; WGCNA further identified salinity-correlated modules involved in ion transport and ribosome biogenesis. Histological alterations remained within physiological ranges with no salinity-dependent severity gradient, as confirmed by semi-quantitative scoring. These findings demonstrate that triploid rainbow trout gills employ distinct molecular strategies at medium versus high salinity. Within the 10–30 ppt range examined, 20 ppt was the salinity at which transcriptional reprogramming was most active, suggesting that this intermediate salinity warrants further investigation as a potential acclimation stage.
Rainbow trout (Oncorhynchus mykiss) is an important cold-water aquaculture species and a tractable salmonid model for functional genomics. Rapid advances in chromosome-level genome assemblies, genetic variation resources, regulatory annotations, tissue and cell models, controlled challenge systems, and genome-editing technologies have established an increasingly integrated framework for linking genomic variation with measurable phenotypes. Evidence from studies of mucosal immunity, disease-resistance genetics, and environmental stress responses indicates that these resources can improve candidate-gene prioritization and mechanistic interpretation across molecular, cellular, tissue, and whole-fish levels. However, differential gene expression, quantitative trait locus and genome-wide association signals, genomic predictions, and cell-type localization remain largely associative and rarely provide direct evidence of causality. Interpretation is further complicated by salmonid-specific whole-genome duplication, because retained paralogues may exhibit tissue-specific divergence, functional redundancy, and compensatory responses. Further progress will require the integration of pangenomics, regulatory annotation, single-cell and spatial analyses, and paralogue-aware functional perturbation in both cell-based and whole-fish systems. Such integration will strengthen causal inference, clarify genotype–phenotype relationships, and support disease-resistant breeding, healthy aquaculture, and environmental risk assessment.
Copper nanoparticles (Cu-NPs) are widely used in aquaculture for their growth-promoting and immunoenhancing properties. However, excessive or over-accumulated Cu-NPs in aquaculture water cause toxicity through waterborne immersion. To explore the toxicity effects of waterborne Cu-NPs on yellowtail kingfish (Seriola aureovittata), a 7-day exposure experiment comprising a control group (no Cu-NPs), a low-concentration group (0.120 mg/L), and a high-concentration group (0.384 mg/L) was conducted, followed by a 7-day recovery period without Cu-NP stress. Exposure to Cu-NPs significantly elevated antioxidant enzyme activities (GSH-Px, Cu/Zn-SOD) and thiobarbituric acid reactive substances (TBARS) level in liver and posterior kidney, indicating significant oxidative stress. In the liver, levels of epinephrine and diacylglycerol were significantly upregulated, the cAMP signaling pathway was disrupted, and the NF-κB signaling pathway was activated, along with the downregulation of ap-1 and erk1-2 and upregulation of gadd45β, reducing cell proliferation and viability. These alterations resulted in hepatocellular vacuolation and blurred outlines of hepatic lobules. In the gill, high-concentration Cu-NPs activated oxidative phosphorylation, phagosome, and cell-adhesion molecules pathways and downregulated genes related to cell proliferation, adhesion, and tight junctions (i.e., l1cam, camd1, cntn1, cdh2, and nectin1), leading to cellular vacuolization and epithelial separation in histology. These changes disrupted osmotic balance and significantly upregulated Na+/K+-ATPase activity. All histological damages were not fully recovered within the tested recovery period. Therefore, under conditions of continuous exposure, the concentration of Cu-NPs used for juvenile yellowtail kingfish in aquaculture should be kept below 0.120 mg/L, with a recovery period exceeding 7 days. These results reveal the toxicity mechanisms of Cu-NPs and provide a scientific basis for establishing safe application guidelines in yellowtail kingfish aquaculture.
Proliferative kidney disease (PKD), caused by the myxozoan parasite Tetracapsuloides bryosalmonae, represents a major threat to salmonid populations and aquaculture, particularly under warming environmental conditions. In Italy, its distribution remains poorly documented. This study aimed to update the epidemiological status of PKD by investigating its occurrence in a trout farm (Piedmont, northwestern Italy), a previously unreported area. A total of 787 individuals of Oncorhynchus mykiss were sampled between May and October 2024 across three seasonal periods. Fish were examined using necropsy, bacteriological, and molecular analyses. Water temperature ranged from 12.4 to 20.3 °C, showing a clear seasonal trend. Overall PKD prevalence was 42.3%, with significant temporal variation, increasing from 23.0% in early summer to 73.0% in late summer, and declining to 3.9% in autumn. A multivariable logistic regression model showed that PKD-positive fish had a lower probability of presenting macroscopic lesions, while sampling period was the main predictor of infection. These results revealed a temporal mismatch between pathological and molecular findings, highlighting the need for further histopathological validation of the observed seasonal patterns. This study provides the first evidence of PKD in southwestern Piedmont, extending the currently documented distribution of the disease in Italy and highlighting the need for enhanced surveillance under climate change.
Piscidins, fish-specific antimicrobial peptides (AMPs), play important roles in the innate immunity of fish against invading bacteria. In this study, a novel piscidin was identified in largemouth bass (Micropterus salmoides) (MSPiscidin-4), which contained an active peptide of 25 aa with an amphipathic helix possessing distinct hydrophobic and positively charged regions. MSPiscidin-4 belongs to the Group I piscidins as determined by sequence identity, homology modeling and phylogenetic tree analysis. MSPiscidin-4 was constitutively expressed in all seven selected tissues, with the highest transcript level in the gill and the lowest in the brain and spleen. Furthermore, MSPiscidin-4 was significantly up-regulated in spleen from 6 h to 24 h post-lipopolysaccharide (LPS) stimulation. A synthetic MSPiscidin-4 peptide was produced by the Fmoc solid-phase synthesis method and exhibited antibacterial activity against several aquatic bacterial strains, with the strongest against Aeromonas hydrophila, followed by Vibrio splendidus, Staphylococcus aureus, Edwardsiella tarda, and the weakest against E. coli and A. veronii. MSPiscidin-4 is the fourth piscidin reported in largemouth bass, showing distinct sequence identity (35.0–68.0% with previously reported MSPiscidins), physicochemical properties (net charge +5, pI 12.48), tissue distribution (highest expression in gill), and antibacterial potency (particularly strong against A. hydrophila). Our results enrich the piscidin components and deepen the understanding of piscidins against invading bacteria in largemouth bass.
Recreational fisheries contribute significantly to global economies through tourism, employment, and ecosystem service valorization. However, a systematic understanding of their economic magnitude and regional disparities remains fragmented. This study conducts a systematic review of 112 peer-reviewed articles published between 1991 and 2024, synthesizing the economic evidence across three key domains: consumer behavior, resource management, and ecological interactions. Consistent with previous research, our systematic synthesis documents a pronounced imbalance in the existing evidence base: studies from high-income countries more frequently report established management frameworks (e.g., bag limits, catch-per-unit-effort monitoring) and robust economic valuation mechanisms (e.g., Willingness to Pay estimation), whereas low- and middle-income countries face significant barriers in infrastructure and resource quantification. We identify that non-market valuation methods, particularly the travel cost method and consumer surplus analysis, are critical for internalizing the environmental value of fisheries. Furthermore, while ecological restoration demonstrates clear positive feedback loops for local economies, the sector exhibits high vulnerability to external shocks, such as the COVID-19 pandemic. This review highlights the urgent need to bridge the data gap in developing regions and suggests that transferring successful adaptive management models from developed nations is essential for achieving equitable and sustainable growth in the global recreational fishery economy.
Tenacibaculosis, caused by Tenacibaculum maritimum, remains a major bacterial disease affecting marine aquaculture, particularly European seabass farming. This study evaluated the immune response and protective efficacy of a formalin-inactivated T. maritimum vaccine administered by immersion or intraperitoneal (i.p.) injection in European seabass (Dicentrarchus labrax). Each vaccination strategy was evaluated using its corresponding experimental challenge model 36 days post-vaccination. Vaccine performance was assessed by relative percentage of survival (RPS), expression of selected immune-related genes (IL-1β, IL-10, IgT), and specific serum IgM production. Intraperitoneal vaccination followed by i.p challenge provided significant protection, with 87% survival and an RPS of 67, accompanied by elevated serum IgM levels and pronounced systemic immune activation. Immersion-vaccinated fish also showed complete survival; however, the unexpectedly low mortality in the corresponding mock-vaccinated controls limited the discriminatory capacity of the immersion challenge model and prevented a robust assessment of vaccine efficacy according to the defined criteria. Gene expression analysis revealed distinct immune profiles, with immersion vaccination inducing an early but transient response, whereas i.p. vaccination elicited stronger and more sustained systemic activation, particularly within innate and humoral immune pathways. Principal component analysis further demonstrated clear clustering of immune responses according to vaccination route. These findings demonstrate the potential of an autogenous vaccine to protect European seabass against tenacibaculosis and highlight the importance of considering both vaccination route and the challenge model when interpreting vaccine efficacy. Further studies should optimise immersion vaccination protocols and investigate local mucosal immune responses to support the development of effective vaccination strategies for juvenile European seabass.
