Dietary mixtures of Bacillus spp. modulates intestinal morphology, resistance to Vibrio parahaemolyticus, response of immune-antioxidant genes, and growth of Dicentrarchus labrax

Fasting, crowding and temperature effects on the cardiac activity of European seabass during ice-slurry slaughtering procedure

Lactococcus garvieae is an emerging pathogen responsible for lactococcosis, a haemorrhagic septicemia affecting fish associated with high mortality and widespread distribution. The disease primarily affects rainbow trout ( Oncorhynchus mykiss ), but L. garvieae has also been reportedin various freshwater and marine fish species, as well as in mammals, including humans. This study describes the first documented outbreaks of L. garvieae in gilthead sea bream ( Sparus aurata ), occurring in the Gulf of Follonica (Tuscany, Italy), following a previous episode in European sea bass ( Dicentrarchus labrax ) in the same area in 2023. Affected fish showed erratic and uncoordinated swimming. Macroscopic lesions included ocular and skin lesions, pericarditis, splenomegaly and haemorrhages in internal organs. Histopatological findings revealed severe fibrinous-necrotic pericarditis and epicarditis associated with bacterial aggregates and widespread granulomatous inflammation in the liver and spleen. Identification of L. garvieae was achieved employing multiple techniques: biochemical tests, miniaturized Analytical Profile Index (API rapid ID 32 strep, Biomerieux), MALDI-TOF MS (MicroFlex LT, Bruker), and molecular methods, including two independent end-point PCR assays followed by sequencing of the 16S–23S ITS region and DNA gyrase subunit B (gyrB) gene. Antimicrobial susceptibility testing of selected isolates was carried out using disk diffusion and minimum inhibitory concentration (MIC) methods, following standardised guidelines. This study presents new data on the characteristics of lactococcosis in gilthead sea bream ( Sparus aurata ), confirming Lactococcus garvieae as a primary pathogen and highlighting its potential impact on Mediterranean aquaculture, as well as the importance of implementing preventive strategies, including vaccination.

Lactococcus petauri is an emerging bacterial pathogen associated with disease outbreaks in freshwater and marine fish species worldwide. While it has been increasingly reported in countries bordering the Mediterranean Sea, no official records of L. petauri have yet been made in Italy for saltwater species. This study reports, for the first time, the presence of L. petauri in European seabass (Dicentrarchus labrax) farmed in land-based tanks along the south-western coast of Italy, based on a retrospective analysis of previously isolated strains. Although only a single isolate was positive, the finding is of notable significance as it originated from a sample collected in 2012. This temporal aspect highlights the likelihood that L. petauri has been circulating in Italian aquaculture systems for at least a decade. The isolate also exhibited a broad antimicrobial resistance profile, including resistance to amoxicillin, fluoroquinolones and trimethoprim/sulfamethoxazole. The historical misidentification of L. petauri is linked to its clinical similarity with Lactococcus garvieae. This highlights the value of re-analysing archived strains with modern tools and underlines the need for accurate diagnostics in aquaculture. The detection in D. labrax extends the known host range and suggests a longer, undetected presence in the Mediterranean.

The objective of the present study was to ascertain the effect of diverse organic feeds (25ECO, 30ECO, and 35ECO) containing varying levels of fishmeal (25%, 30%, and 35%) on the growth and fillet quality of juvenile sea bass. The ECO diets were composed of a blend of organic vegetable proteins. The control diet contained 30% fishmeal without any organic ingredients. The experimental period spanned 196 days, during which the fish were fed twice daily, with an initial mean weight of 40 g. The results indicated that reducing fishmeal to 25% in the 25ECO diet negatively affected growth and increased feed consumption. The 30ECO diet, which contains 30% fishmeal, exhibited no adverse effects; however, its biometric outcomes diverged from those of the control diet. The 25ECO diet demonstrated superior Met retention levels, and certain free amino acids that enhance flavour (SER, ALA, ASP, and GLU) exhibited higher concentrations in fillets from fish fed ECO diets (35ECO and 30ECO). No substantial disparities were observed in the fatty acid profile or fillet nutritional indexes, which were deemed to be satisfactory and conducive to good health. From an economic perspective, the 30 ECO diet was deemed optimal and exhibited the greatest inclination towards purchase.

Understanding the structure and function of estuarine fish communities is essential for guiding ecosystem-based management and restoration. This study investigated long-term patterns in fish community composition, abundance, species richness and estuarine use across 15 nearshore sites within three estuaries and the Isle of Wight, located in the Solent, a large temperate estuarine system in southern England. Using a 12-year dataset (2007-2018) of biannual seine net surveys, we applied traditional community metrics alongside functional guild classifications and Fish Estuarine Association Scores (FEAS) to assess spatio-temporal variation and estuarine dependency. A total of 55 species were recorded, with six species (Atherina presbyter, Dicentrarchus labrax, Pomatoschistus microps and Chelon auratus and the family Clupeidae) accounting for 96% of individuals. Marine migrants and estuarine residents dominated the assemblage, indicating strong connectivity between estuarine and coastal habitats. While fish abundance declined significantly over time, species richness and community composition varied across seasons, tidal states and spatial scales. Sites and catchments differed markedly in FEAS, with some areas supporting species more dependent on estuarine habitats. These results highlight the importance of multisite, seasonal monitoring and the value of trait-based metrics in identifying nursery habitats and guiding restoration. The FEAS approach, applied retrospectively to historical data, offers a practical framework for setting ecological baselines and prioritising functionally important estuarine areas under real-world monitoring constraints.

The Anti-Müllerian hormone (AMH) is widely recognized for promoting Müllerian duct regression in higher vertebrates and regulating key reproductive functions like steroidogenesis, folliculogenesis, and Leydig cell development. In teleost fish, which lack Müllerian ducts, Amh primarily influences male reproductive functions, including sex determination, testis differentiation, and germ cell proliferation. In adult fish, Amh supports gonad development and spermatogenesis, but its role in teleost gonadal physiology remains largely underexplored. This study reveals a novel steroidogenic function in the European sea bass (Dicentrarchus labrax) using in vitro testis culture, in vivo plasmid injection, and cell-based transactivation assays. The Amh-induced significant increase in androgen levels was also confirmed in Japanese medaka (Oryzias latipes) treated with recombinant sea bass Amh. Beyond activating the canonical Smad pathway, Amh also triggered the cAMP/PKA signalling pathway via its cognate type II receptor, Amhr2. Inhibitors of these pathways independently and synergistically counteracted Amh-induced CRE-Luc activity, indicating pathway crosstalk. Moreover, inhibition of the cAMP pathway suppressed Amh-induced androgen production in testis cultures, emphasizing the crucial role of protein kinase A in mediating Amh steroidogenic action. These findings uncover a novel steroidogenic function of Amh in teleosts and highlight its broader role in male reproductive physiology.

Synergistic effects of dried Padina sp. and prebiotic on growth, histology, and growth-related gene expression in European seabass (Dicentrarchus labrax)

Abstract This study evaluated POET CFP, a corn‐fermented protein derived from dry‐mill bioethanol production, as a potential candidate for use in European seabass aquafeeds. The apparent digestibility coefficients (ADC) of POET CFP were evaluated and compared to soybean meal. The ADC of POET CFP protein was higher than that of soybean meal (92.7% vs. 83.9%), and the neutral detergent fiber (NDF) of POET CFP was partially digested (26%), while that of soybean meal was completely undigestible. However, the ADC of energy was similar between the two feedstuffs (70%). Two growth trials were performed to evaluate the effect on growth performance and feed utilization of European seabass for total or partial replacement of corn gluten meal (CGM) (Trial 1) or CGM and soybean meal (CGM + SBM) (trial 2) with POET CFP. For that purpose, a practical diet with 48% protein and 18% lipids was formulated to include 20% fish meal, 15% CGM, and 15% SBM (control diet). For trial 1, four diets similar to the control were formulated with POET CFP replacing CGM at 25%, 50%, 75%, and 100%. For trial 2, three other diets similar to the control were formulated, but POET CFP replaced CGM + SBM at 33%, 66%, and 100%. Triplicate groups of European seabass juveniles with 26 g were fed these diets for 85 days. Results of Trial 1 showed that total dietary replacement of CGM with CFP did not affect growth performance, feed intake, feed utilization, and whole‐body composition. N retention (% N intake) was also unaffected, but energy retention (% energy intake) linearly increased with dietary CFP inclusion. Further, the histomorphological appearance of the posterior intestine was unaffected by dietary CFP inclusion. Results of trial 2 showed that total dietary replacement of CGM + SBM with CFP did not affect growth performance, feed intake, feed utilization, and N and energy retention (% intake). However, polynomial contrasts showed a significant linear trend for increased growth performance and feed efficiency with the dietary inclusion of CFP. Whole‐body dry matter and lipid content linearly decreased with the dietary increase of CFP. No differences were observed between groups in the histomorphological appearance of the distal intestine. This study showed that CFP could completely replace CGM and SBM in diets for European seabass juveniles without affecting growth performance and feed utilization or adversely affecting posterior intestine morphology.

The present study investigates the impact of refrigeration storage on the freshness and shelf life of European sea bass (Dicentrarchus labrax). This investigation utilises computer vision systems and artificial neural networks (ANNs) to analyse the dynamics of the process. A non-destructive assessment approach was established by analysing the eye colour characteristics (RGB, Lab*, and HSI values) of fish stored at +4 °C for 15 days, with sampling occurring every three days. There were considerable changes in the colour range throughout the time, particularly a reduction of brightness (L*), which can be one indicator of the progressive deterioration of the fish›s freshness. The neural network multilayer perceptron was optimised with 20 neurons in the hidden layer and demonstrated a high correlation coefficient (R² = 0.98) between predicted and experimental shelf life values. The data indicates that the values of rack life, which were initially determined to be cautious, exhibited a high degree of correlation with the estimated values. The R2 value was determined to be 0.98. The technique offers a rapid and reliable non-destructive method for determining the freshness of fish, with potential applications in relevant areas such as quality control and natural security examination for aquaculture products. The present study investigates the impact of refrigeration storage on the freshness and shelf life of European sea bass (Dicentrarchus labrax). This investigation utilises computer vision systems and artificial neural networks (ANNs) to analyse the dynamics of the process. A non-destructive assessment approach was established by analysing the eye colour characteristics (RGB, Lab*, and HSI values) of fish stored at +4 °C for 15 days, with sampling occurring every three days. There were considerable changes in the colour range throughout the time, particularly a reduction of brightness (L*), which can be one indicator of the progressive deterioration of the fish›s freshness. The neural network multilayer perceptron was optimised with 20 neurons in the hidden layer and demonstrated a high correlation coefficient (R² = 0.98) between predicted and experimental shelf life values. The data indicates that the values of rack life, which were initially determined to be cautious, exhibited a high degree of correlation with the estimated values. The R2 value was determined to be 0.98. The technique offers a rapid and reliable non-destructive method for determining the freshness of fish, with potential applications in relevant areas such as quality control and natural security examination for aquaculture products.

Background: Fish escape events from aquaculture facilities are increasing and pose significant ecological, economic, and traceability concerns. Accurate methods to differentiate between wild, cultured, and escaped fish are essential for fishery management and seafood authentication. Methods: This study analyzed muscle tissue from Sparus aurata, Dicentrarchus labrax, and Argyrosomus regius using a multiomics approach. Heavy metals were quantified by ICP-MS, fatty acid profiles were assessed via GC-MS, and metabolomic and lipidomic signatures were identified using 1H NMR spectroscopy. Multivariate statistical models (MDS and PLS-LDA) were applied to classify fish origins. Results: Wild seabream showed significantly higher levels of arsenic (9.5-fold), selenium (3.5-fold), and DHA and ARA fatty acids (3.2-fold), while cultured fish exhibited increased linoleic and linolenic acids (6.5-fold). TMAO concentrations were up to 5.3-fold higher in wild fish, serving as a robust metabolic biomarker. Escaped fish displayed intermediate biochemical profiles. Multivariate models achieved a 100% classification accuracy across species and analytical techniques. Conclusions: The integration of heavy metal analysis, fatty acid profiling, and NMR-based metabolomics enables the accurate differentiation of fish origin. While muscle tissue provides reliable biomarkers relevant to human exposure, future studies should explore additional tissues such as liver and gills to improve the resolution of traceability. These methods support seafood authentication, enhance aquaculture traceability, and aid in managing the ecological impacts of escape events.

Cultivated fish can offer seafood with lower environmental impact and improved animal welfare. Electrospun fibres, resembling collagen in structure and size, can mimic the myoseptum -an important structural element for fish fillet patterning. Here, we cultured Dicentrarchus labrax Embryonic Cells (DLEC) for the first time on edible zein-gelatin electrospun fibres. Notably, we successfully incorporated biomass of the microalgae Nannochloropsis oceanica into the fibres. The effect of the Maillard reaction as thermal crosslinking method was studied. The structure, chemical composition, mechanical performance and biocompatibility of the electrospun fibres were evaluated. Fibres containing N. oceanica biomass significantly enhanced DLEC adhesion, leading to faster proliferation. Aligned fibres promoted DLEC alignment, an important feature for improving texture in food products. Finally, the fibrous scaffolds and edible bioinks were successfully combined to fabricate a cultivated fish prototype. Overall, these findings highlight the potential of edible electrospun fibres for the development of cultivated fish fillets.

In the current study, gilthead sea bream (n = 100) and European sea bass (n = 100), with suspected infection by P. damselae, which showed skin lesions, were sampled under aquaculture conditions. P. damselae was diagnosed by the BD Phoenix rapid diagnosis system, and its subspecies were identified by polymerase chain reaction. Initially, BD Phoenix identified 26 Photobacterium damselae isolates from all tissue samples. Also, as to polymerase chain reaction analysis, 8 isolates from 26 identified isolates showed positive results for the 16S rRNA, ureC, and CPS genes and were identified as P. damselae subsp. damselae. On the other hand, isolates (n = 18) with 16S rRNA and CPS gene-positive and ureC gene-negative results were defined as P. damselae subsp. piscicida. Antibiotic tests showed that P. damselae subsp. damselae isolates were susceptible to amoxicillin-clavulanic acid, ciprofloxacin, cefotaxime, and ampicillin. Conversely, P. damselae subsp. piscicida isolates were sensitive to ciprofloxacin and gentamicin.

Understanding compensatory growth in European sea bass (Dicentrarchus labrax) is also crucial for optimizing aquaculture practices as it can lead to more efficient feeding strategies and improved fish health. To this end, this study evaluated the effects of fasting and re-feeding on growth performance, mineral and antioxidant enzyme activities of European sea bass fingerlings. The experiment involved five treatments, each with three replicates. The control treatment was fed continuously, while treatments A1, A2, A3, and A4 were fasted for one, two, three, and four weeks, respectively. Following the fasting period, all treatments were fed to satiation twice daily for four weeks. At the end of the trial, the control treatment showed the best growth during the fasting period, while the growth of the other treatments decreased with the duration of fasting (p

Synthetic flavors from standardized processes have recently emerged as a promising and sustainable alternative to traditional feed attractants. In this study, two attractive (F25, cheese; F35, caramel) and one repulsive (F32-, coconut) synthetic flavors were individually added (1% w/w) to a commercial diet for European seabass (Dicentrarchus labrax) and tested over a 90-day feeding trial (30 fish per tank, in triplicate; initial weight 72.48 ± 8.04 g) to assess their impact on fish growth performance, welfare, and the modulation of brain appetite and monoaminergic pathways. None of the tested flavors negatively affected overall fish health. The F35 flavor enhanced feed intake (90.1 ± 5.6%) and growth (SGR 2.2 ± 0.2%) and positively influenced appetite-related and monoaminergic signals, thus being more effective than the F25 one (80.4 ± 3.2 and 1.6 ± 0.1%, respectively). A weekly feeding rotation between F35 and F25 (ROT group) resulted in suboptimal outcomes compared to F35 administration alone. The F32- flavor was not clearly perceived as strongly aversive by seabass and did not impair zootechnical performance. These findings highlight the potential of attractive synthetic flavors to improve diet palatability in a carnivorous species of commercial value, offering novel insights for more sustainable and cost-effective aquaculture feeding strategies.

Ain Al-Ghazala Lagoon, located along the northeastern Mediterranean coast of Libya, is a key coastal ecosystem with rich biodiversity. This study aims to assess the fish species composition and their ecological roles within the lagoon. Fish samples were collected in summer and winter of 2024, with the assistance of local fishermen, and analyzed based on their morphological characteristics. The findings revealed a diverse range of species from the class Actinopterygii, occupying various habitats, including brackish and rocky reef environments. Several species, such as Atherina boyeri and Mugil cephalus, serve as important prey for higher trophic-level predators, while apex predators like Epinephelus marginatus play a key role in maintaining the food web balance. Many species, including Dicentrarchus labrax and Sparus aurata, have significant economic value in regional fisheries and aquaculture. However, the lagoon also faces ecological threats from invasive Lessepsian species, such as Siganus luridus and Pterois miles, which disrupt local ecosystems and pose risks to biodiversity. The study underscores the need for effective management strategies to conserve the lagoon’s biodiversity and ensure sustainable fisheries. Further research is required to assess the impact of invasive species and to address the combined challenges of overfishing, climate change, and habitat degradation.

We compared tolerance of acute progressive hypoxia and warming in the three recognized populations of European seabass, Atlantic (AT), West Mediterranean (WM) and East Mediterranean (EM), that have evolved within a North-West to South-East thermal gradient, from AT to EM. We reared progeny of captive broodstock in common garden at two temperatures, 18 and 24°C, representing summer temperatures in Atlantic and East Mediterranean, respectively. At about 1 year of age, hypoxia tolerance was evaluated with static respirometry, as critical saturation for regulation of standard metabolic rate (Scrit) and regulation index (RI); while warming tolerance was evaluated by swimming respirometry, as critical thermal maximum for aerobic swimming (CTSmax). We expected AT fish systematically to be least tolerant and EM most, with WM intermediate. At 18°C, the tolerance traits were similar among populations, but they responded differently when reared at 24°C. In AT and WM, Scrit increased—tolerance declined—from 18 to 24°C, whereas in EM it did not change. In AT and WM, RI did not change from 18 to 24°C whereas in EM it increased—tolerance increased, and EM had higher RI than WM at 24°C. In AT and EM, CTSmax was similar at 18 and 24°C whereas in WM it increased—tolerance increased, and WM had higher CTSmax than AT and EM at 24°C. Therefore, the EM population is able to avoid negative effects of warmer water on hypoxia tolerance, compared to AT and WM, but this was not related to improved thermal tolerance at the warmer temperature, where WM performed better than AT and EM. Consequently, the seabass exhibits inter-populational variation in tolerance of the stressors but patterns are complex and not consistent between hypoxia and warming. We explored some potential patterns of inter-individual variation in tolerance. We found no evidence that individuals relatively tolerant of hypoxia (low Scrit, high RI) were also relatively tolerant of warming (high CTSmax). There was evidence of complex relationships with body mass, whereby tolerance of warming declined with increasing mass at 18°C but tolerance of hypoxia increased with mass at 24°C. Finally, the traits of tolerance were not dependent on individual standard metabolic rate at either temperature.

Nervous Necrosis Virus (NNV) is a major threat to aquaculture, causing high mortality in farmed fish, including European sea bass. The genetic basis of host response to NNV has been well characterised, suggesting the potential role of interferon-induced genes in resistance to the virus, although the molecular mechanisms underlying NNV infection in sea bass are still debated. The time- and tissue-specific dynamics of gene expression is crucial for understanding host response to NNV. Here, we report on a time-course transcriptome analysis of brain and head kidney in NNV-infected bass that integrated the statistical evidence of differential expression with the information on temporal profiles (i.e. 6, 12, 24, 48, and 72 h post-infection (hpi)) compared to mock-infected controls. Results revealed substantial changes in gene expression over time, particularly for brain, with downregulation of genes involved in nervous system functions and upregulation of immune and inflammatory response genes from 24 to 48 hpi onwards, mostly associated with the interferon (IFN) response. The study highlights tissue-specific differences in the timing and magnitude of the innate immune response compared to other fish species and provides a comprehensive view of the dynamic host response, emphasizing the need for time-course studies in understanding viral pathogenesis.

The anti-Müllerian hormone (amh) and its receptor, amhr2, along with the downstream bone morphogenetic protein receptors (bmprs), have been recognized as the central regulators in teleost sex determination (SD) and differentiation. However, their evolution and function in reproduction among diverse teleost lineages may represent species-specific patterns and still need more explanation. In this study, systematic investigations of amh signaling genes, including amh, amhy (Y-linked paralog of amh), amhr2, bmpr1, and bmpr2, were conducted among teleost species. The results revealed generally conserved gene copy number, phylogeny, structure, and synteny, among teleost amh signaling genes. Notably, significantly accelerated evolutionary rates (dN/dS) were found in teleost amhy compared to amh, and amh exhibited faster molecular evolution in amhy-SD teleosts than in non-amhy-SD teleosts, suggesting their enhanced evolutionary plasticity in teleosts. Expression profiling identified testis-biased expression of the most amh signaling genes in fish species with different SD genes and mechanisms, including Lateolabrax maculatus and Dicentrarchus labrax from Order Perciformes, Cynoglossus semilaevis and Paralichthys olivaceus from Order Pleuronectiformes, and Salmo salar and Oncorhynchus mykiss from Order Salmoniformes, with ovary-biased expression also found in Salmoniformes. A weighted gene co-expression network analysis further uncovered strong species-specific functional interactions between amh signaling components and genes of germ-cell development, the meiotic process, etc. Collectively, the integrated evidence from this study supports the hypothesis that amh signaling provides the key molecules governing sex differentiation in a species-specific manner in diverse teleost lineages, independent of its SD role, and interacts with functions of both testis and ovary development.

Toxicity of 6PPD-quinone in European seabass (Dicentrarchus labrax) under baseline and Vibrio alginolyticus challenge conditions: Protective insights from astaxanthin mitigation.