Search Results (32)

The aquaculture sector is essential for meeting seafood demand while ensuring sustainability. It involves farming fish, mollusks, crustaceans, other invertebrates, and algae in controlled environments, helping to conserve marine resources and reduce ecological pressures. Sustainable practices, such as an integrated multitrophic recirculating aquaculture system (IMTA-RAS) with fish and seaweed, can minimize the environmental impact of fish aquaculture. However, the impact of the introduction of macroalgae on the fish muscle metabolism has not been studied. This research examines the impact of growing Senegalese sole (Solea senegalensis) together with sea lettuce (Ulva ohnoi) on fish metabolism using high-resolution ¹H-NMR-based metabolomics. Three farming systems were compared. These were E₁, a recirculating aquaculture system (RAS); E₂, an IMTA-RAS integrating U. ohnoi for biofiltration; and E₃, an IMTA-RAS with U. ohnoi and Phaeobacter sp. strain 4UAC3, a probiotic bacterium isolated from wild U. australis known to counteract fish pathogens. A metabolomic analysis revealed that energy metabolism was enhanced in IMTA-RAS and even more in IMTA-RAS-Phaeobacter–grown fish, increasing overall metabolic activity. These results indicate that the presence of the algae with the probiotic had a clear impact on the physiological state of the fish, and this deserves further investigation. This study contributes to the understanding of the physiological responses of fish to innovative aquaculture practices, supporting the development of more sustainable and efficient management that reduces the environmental impact and increases fish health and welfare. Full article

Fish exhibit diverse mechanisms of sex differentiation and determination, shaped by both external and internal influences, often regulated by distinct DNA methylation patterns responding to environmental changes. In S. senegalensis aquaculture, reproductive issues in captivity pose significant challenges, particularly the lack of fertilization capabilities in captive-bred males, hindering genetic improvement measures. This study analyzed the methylation patterns and transcriptomic profiles in gonadal tissue DNA from groups differing in rearing conditions and sexual maturity stages. RRBS (Reduced Representation Bisulfite Sequencing) was employed to detect notable methylation variations across groups, while RNA was extracted and sequenced for differential expression analysis. Our findings suggest that DNA methylation significantly regulates gene expression, acting as a mechanism that can both repress and enhance gene expression depending on the genomic context. The complexity of this epigenetic mechanism is evident from the varying levels of methylation and correlation rates observed in different CpGs neighboring specific genes linked to reproduction. Differential methylation comparisons revealed the highest number of differently methylated CpGs between maturation stages, followed by rearing conditions, and lastly between sexes. These findings underscore the crucial role of methylation in regulating gene expression and its potential role in sex differentiation, highlighting the complex interplay between epigenetic modifications and gene expression. Full article

Biotic samples from Algeciras Bay (South-west Europe) were studied to assess its ecological status, complementing the previous abiotic monitoring of trace metals in water and sediments. This bay is a densely populated area with intense port traffic and is highly industrialised with metal inputs. To study the impact of this, Zn, Cd, Pb, and Cu contents were determined in tissues of benthic (Solea senegalensis) and benthopelagic species (Scorpaena porcus, Trigloporus lastoviza, and Diplodus sargus sargus). Notable levels of Zn and Cu were found in the liver and gills of all fish species. Compared to international muscle guidelines, Pb sometimes exceeded the most restrictive values, outstanding S. porcus with 27% of samples above the permissible value. Metal pollution indexes revealed that the liver and gills of benthic species were more affected by metal pollution than benthopelagic species, especially in most industrialised sites. Particularly, S. senegalensis presented a higher accumulation factor from sediment of Cd and Cu in the liver (30.1 and 345.1), probably due to the close interaction as benthic species. Among the species studied, S. senegalensis and D. sargus sargus proved to be the best representative and useful bioindicators of metal-polluted environments as this bay. The results were consistent with the findings from the abiotic samples. Full article

Tenebrio molitor (TM) is considered as one of the most promising protein sources for replacing fish meal in aquafeeds, among other things because it is rich in protein, a good source of micronutrients and has a low carbon footprint and land use. However, the main drawback of TM is its fatty acid profile, in particular its low content of n-3 PUFA. This study evaluates the effects of partially replacing plant or marine-derived with full-fat TM meal at two different levels on growth performance and lipid profiles of Senegalese sole (Solea senegalensis). For this purpose, a control diet (CTRL) and four experimental isoproteic (53%) and isolipidic (16%) diets were formulated containing 5 and 10% TM meal replacing mostly fish meal (FM5 and FM10), or 10 and 15% TM meal replacing mostly plant meal (PP10 and PP15). Fish (215 g) were fed at 1% of their body weight for 98 days. The final body weight of fish fed the experimental diets containing TM meal was not different from that of fish fed the CTRL diet (289 g). However, the inclusion of TM meal resulted in a gradual improvement in growth rate and feed efficiency in both cases (replacement of fish or plant meals), and significant differences in specific growth rate (SGR) were observed between fish fed the CTRL diet (SGR = 0.30% day⁻¹) and those fed diets with the highest TM meal content (PP15; SGR = 0.35% day⁻¹). The experimental groups did not show any differences in the protein content of the muscle (19.6% w/w). However, significant differences were observed in the total lipid content of the muscle, with the FM10, PP10, and PP15 groups having the lowest muscle lipid contents (2.2% ww). These fish also showed the lowest neutral lipid content in muscle (6.6% dw), but no differences were observed in the total phospholipid content (2.6% dw). Regarding the fatty acid profile, fish fed FM10, PP10 and PP15 had lower levels of linoleic acid (18:2n-6) and higher levels of oleic acid (18:1n-9) in liver and muscle compared to fish fed CTRL. However, no differences were found between fish fed CTRL and TM-based diets for docosahexaenoic acid (22:6n-3) and total n-3 PUFA in liver and muscle. In conclusion, our study demonstrated that full-fat TM inclusion up to 15% in S. senegalensis diets had no negative effects or even some positive effects on fish survival, growth performance, nutrient utilization and flesh quality. Full article

Some of the characteristics of probiotics used in aquaculture are the antagonistic activity against pathogens and the activation of the immune response. Moreover, some probiotics with common antigens to pathogens can produce antibodies that react with these pathogens. One of those potential probiotics is Vibrio proteolyticus DCF12.2, a strain with the capacity to produce antibodies in soles (Solea senegalensis) that react with Photobacterium damselae subsp. piscicida and Vibrio harveyi antigens. Therefore, the objective of the work was to determine the capacity of DCF12.2 to activate the immune response in the sole, providing protection against both pathogens. For this purpose, DCF12.2 was administered to cultured soles by intraperitoneal injection, bath, and diet. The DCF12.2 strain activated the gene expression related to the fish immune response and increased the antibody production with cross-reaction to P. damselae subsp. piscicida and V. harveyi cells. Challenges with P. damselae subsp. piscicida resulted in a 30–40% relative percent survival (RPS) through DCF12.2 treatments. After challenge with V. harveyi, only intraperitoneal treatment protected the fish (67% RPS). In conclusion, the DCF12.2 strain showed great potential to be used to prevent diseases caused by both pathogens, and indicates a way to use probiotics as live vaccines. Full article

Taurine is a sulphur-containing amino acid with important physiological roles and a key compound for the synthesis of bile salts, which are essential for the emulsion and absorption of dietary lipids. This study aimed to evaluate the effects of taurine supplementation to low-fishmeal diets on the metabolism of taurine, bile acids, and lipids of Senegalese sole. A fishmeal (FM) and a plant-protein-based (PP0) diet were formulated, and the latter was supplemented with taurine at 0.5 and 1.5% (diets PP0.5 and PP1.5). Diets were assigned to triplicate tanks containing 35 fish (initial weight ~14 g) for 6 weeks. Fish from the PP0 treatment presented lower taurine and bile-acid concentrations compared with the FM treatment, and a downregulation of cyp7a1 and abcb11 was observed. Triolein catabolism decreased in PP0-fed fish, resulting in increased hepatic fat content and plasma triglycerides, while no effects on plasma cholesterol were observed. Taurine supplementation to plant-based diets resulted in a higher taurine accumulation in fish tissues, increased bile-acid concentration, and upregulation of cyp7a1 and abcb11. Hepatic fat content and plasma triglycerides decreased with increasing dietary taurine supplementation. Taurine supplementation mitigated part of the negative effects of plant-based diets, leading to better lipid utilisation. Full article

Physical complexity adds physical enrichment to rearing conditions. This enrichment promotes fish welfare and reduces detrimental characteristics that fish develop in captivity. Senegalese sole (Solea senegalensis) is an important species for European aquaculture, where it is reared in intensive conditions using fibreglass tanks. However, reproductive dysfunctions present in this species do not allow it to complete its life cycle in captivity. Recently, dominance behaviour has been studied to try to solve this problem. The present study aimed to assess the effect of sand as environmental enrichment in the dominance behaviour and brain mRNA abundance of Senegalese sole juveniles. Four tanks of sole (n = 48 fish in total) were established in two different environments (with and without sand). Juveniles were subjected to dominance tests of feeding and territoriality. Behaviours analysed by video recordings related to the distance from the food delivered and harassment behaviour towards other individuals (e.g., resting of the head on another individual). In both environments, dominant sole were the first to feed, displayed more head-resting behaviour and dominated the area close to the feeding point, where the events were reduced in fish maintained in the sand. mRNA expression related to differentiation of dopamine neurons (nr4a2) and regulation of maturation (fshra) were significantly upregulated in dominant fish in the sand environment compared to dominants maintained without sand. The use of an enriched environment may affect Senegalese sole dominance, enhance welfare and possibly advance future maturation. Full article

Endolimax is a genus of intestinal amoebae which stands among the least known human protists. Previous studies on amoebic systemic granulomatosis of a marine fish (Solea senegalensis) resulted in the unexpected characterization of a new organism which was related to Endolimax and named E. piscium. The existence of multiple reports of systemic granulomatosis caused presumptively by unidentified amoebae in goldfish lead us to investigate the organism involved in goldfish disease. Analysed goldfish presented small whitish nodules in the kidney, which correspond to chronic granulomatous inflammatory reactions with a ring-layer of amoebae in the periphery. Amoebae were amitochondriate and were located in a parasitophorous vacuole within macrophages, as previous studies on this condition in goldfish and other freshwater fish pointed out. SSU rDNA characterization confirmed a new Endolimax lineage which appears closely related to E. piscium, but the molecular evidence, distinct pathological features and lack of ecological overlapping between the hosts support their assignment to a new species, E. carassius. The results support the existence of a considerable unexplored diversity of Endolimax spp. among fish, and their proper characterization can contribute to an understanding of Archamoebae evolution and pathogenic potential. Full article

Histological techniques are a traditional and essential tool for adequately comprehending cellular morphology and physiology in several scientific fields, including ecotoxicological studies. Although bioassays generally recommend using small test organisms, based on advantages such as low maintenance costs and the possibility of a higher number of replicates, the histological process of such organisms is still challenging due to the difficulty of handling them. The present study proposes an accessible protocol for performing the histology of a biological sample of 8 mm maximum length and using histopathological biomarkers in Senegal sole larvae for ecotoxicological tests. Eight-day old larvae of Solea senegalensis obtained from breeders’ natural spawns in cultivation conditions were submitted to histological processing by an adjusted protocol comprising fixation, agarose array pre-embedding, dehydration, paraffin embedding, slides’ preparation, and image analysis by light optical microscope coupled to a digital camera. Low-cost and easy-to-use alternatives were applied in the technique execution. The histological steps were detailed, and S. senegalensis morphological features were presented. This can be considered valuable background information for ecotoxicological studies where changes in cell morphology and physiology are expected. Full article

Research on recruitment variability has gained momentum in the last years, undoubtedly due to the many unknowns related to climate change impacts. Knowledge about recruitment—the process of small, young fish transitioning to an older, larger life stage—timing and success is especially important for commercial fish species, as it allows predicting the availability of fish and adapting fishing practices for its sustainable exploitation. Predicting tools for determining the combined effect of temperature rise and food quality and quantity reduction (two expected outcomes of climate change) on early-life history traits of fish larvae are valuable for anticipating and adjusting fishing pressure and policy. Here we use a previously published and validated dynamic energy budget (DEB) model for the common sole (Solea solea) and adapt and use the same DEB model for the Senegalese sole (S. senegalensis) to predict the effects of temperature and food availability on Solea spp. early life-history traits. We create seven simulation scenarios, recreating RCP 4.5 and 8.5 Intergovernmental Panel on Climate Change (IPCC) scenarios and including a reduction in food availability. Our results show that temperature and food availability both affect the age at metamorphosis, which is advanced in all scenarios that include a temperature rise and delayed when food is limited. Age at puberty was also affected by the temperature increase but portrayed a more complex response that is dependent on the spawning (batch) period. We discuss the implications of our results in a climate change context. Full article

The Senegalese sole (Solea senegalensis, Kaup 1858), a marine flatfish, belongs to the Pleuronectiformes order. It is a commercially important species for fisheries and aquaculture. However, in aquaculture, several production bottlenecks have still to be resolved, including skeletal deformities and high mortality during the larval and juvenile phase. The study aims to characterize the hox gene clusters in S. senegalensis to understand better the developmental and metamorphosis process in this species. Using a BAC library, the clones that contain hox genes were isolated, sequenced by NGS and used as BAC-FISH probes. Subsequently the hox clusters were studied by sequence analysis, comparative genomics, and cytogenetic and phylogenetic analysis. Cytogenetic analysis demonstrated the localization of four BAC clones on chromosome pairs 4, 12, 13, and 16 of the Senegalese sole cytogenomic map. Comparative and phylogenetic analysis showed a highly conserved organization in each cluster and different phylogenetic clustering in each hox cluster. Analysis of structural and repetitive sequences revealed accumulations of polymorphisms mediated by repetitive elements in the hoxba cluster, mainly retroelements. Therefore, a possible loss of the hoxb7a gene can be established in the Pleuronectiformes lineage. This work allows the organization and regulation of hox clusters to be understood, and is a good base for further studies of expression patterns. Full article

Vitamin K (VK) is a fat-soluble vitamin necessary for fish metabolism and health. VK stability as dietary component during aquafeed storage and its potential effect on intestinal microbiome in fish have not yet been completely elucidated. The convenient storage conditions of aquafeeds when supplemented with phylloquinone (VK1), as well as its potential effects on the gut microbiota of Senegalese sole (Solea senegalensis) juveniles, have been explored. Experimental feeds were formulated to contain 0, 250 and 1250 mg kg⁻¹ of VK1 and were stored at different temperatures (4, −20 or −80 °C). VK stability was superior at −20 °C for short-term (7 days) storage, while storing at −80 °C was best suited for long-term storage (up to 3 months). A comparison of bacterial communities from Senegalese sole fed diets containing 0 or 1250 mg kg⁻¹ of VK1 showed that VK1 supplementation decreased the abundance of the Vibrio, Pseudoalteromonas, and Rhodobacterace families. All these microorganisms were previously associated with poor health status in aquatic organisms. These results contribute not only to a greater understanding of the physiological effects of vitamin K, particularly through fish intestinal microbiome, but also establish practical guidelines in the industry for proper aquafeed storage when supplemented with VK1. Full article

Senegalese sole (Solea senegalensis) has been considered a promising new flatfish species for Mediterranean marine fish farming. Accurate prediction of fillet traits in live animals may allow for more efficient control of muscle deposition in fish. In this sense, this study was undertaken to develop a non-invasive method to predict in vivo fish fillet volume and yield using real-time ultrasonography (RTU). The trial was conducted with 44 market weight Senegalese sole (298.54 ± 87.30 g). Fish were scanned with an Aloka SSD 500V with a 7.5 MHz probe. Ten RTU cross-sectional images were taken from the operculum to the caudal fin at regular intervals. These images were analyzed using Fiji software. These data were then used to estimate the partial volumes of the fillet. Actual fillet volume was determined using Archimedes’ principle. Simple and stepwise multiple regression analyses were then used to develop prediction models of fillet volume and yield. The most cranial RTU sections of the fish fillet were the best single predictors of both fillet volume and fillet yield and were the ones included in the best stepwise models. The best RTU slice area explained 82% of the variation observed in fillet volume, but the other RTU slice areas used as predictors of fillet volume showed poor to moderate accuracy (0.035 ≤ R² ≤ 0.615). Single RTU partial volumes showed poor to very high accuracy (0.395 ≤ R² ≤ 0.970) as predictors of fillet volume. The best stepwise model based on the RTU slice areas included three independent variables and explained 88.3% of the observed variation. The best stepwise models based on RTU partial volumes (single volumes and/or combinations of single volumes) explained about 97% of the variation observed in fillet volume. Two RTU volume traits, V_1–5 + V_6–9, and V₁₊₍₎₊₉, showed to be practically direct predictors of the actual fillet volume, explaining, respectively, 97% and 96% of the variation observed in the actual fillet volume. The fillet yields show lower correlations with slice areas (r between 0.044 and 0.601) than with volumes (r between 0.288 and 0.637). While further studies are clearly necessary to better understand the potential of RTU for the estimation of fillet yield in fish in general and Senegalese sole in particular, the present results showed that RTU traits can be very good predictors of Senegalese sole’s fillet volume, either used in regression models or as direct predictors. Full article

The Pleuronectiformes order, which includes several commercially-important species, has undergone extensive chromosome evolution. One of these species is Solea senegalensis, a flatfish with 2n = 42 chromosomes. In this study, a cytogenomics approach and integration with previous maps was applied to characterize the karyotype of the species. Synteny analysis of S. senegalensis was carried out using two flatfish as a reference: Cynoglossus semilaevis and Scophthalmus maximus. Most S. senegalensis chromosomes (or chromosome arms for metacentrics and submetacentrics) showed a one-to-one macrosyntenic pattern with the other two species. In addition, we studied how repetitive sequences could have played a role in the evolution of S. senegalensis bi-armed (3, and 5–9) and acrocentric (11, 12 and 16) chromosomes, which showed the highest rearrangements compared with the reference species. A higher abundance of TEs (Transposable Elements) and other repeated elements was observed adjacent to telomeric regions on chromosomes 3, 7, 9 and 16. However, on chromosome 11, a greater abundance of DNA transposons was detected in interstitial BACs. This chromosome is syntenic with several chromosomes of the other two flatfish species, suggesting rearrangements during its evolution. A similar situation was also found on chromosome 16 (for microsatellites and low complexity sequences), but not for TEs (retroelements and DNA transposons). These differences in the distribution and abundance of repetitive elements in chromosomes that have undergone remodeling processes during the course of evolution also suggest a possible role for simple repeat sequences in rearranged regions. Full article

Nervous necrosis virus (NNV), genus Betanodavirus, the etiological agent of the viral encephalopathy and retinopathy (VER), presents a genome with two positive-sense single-stranded RNA segments. Striped jack nervous necrosis virus (SJNNV) and red-spotted grouper nervous necrosis virus (RGNNV), together with reassortants RGNNV/SJNNV, are the betanodaviruses predominantly isolated in Southern Europe. An RGNNV/SJNNV reassortant isolated from Senegalese sole (wt160) causes high mortalities in this fish species. This virus presents differences in the sequence of the 3’ non-coding region (NCR) of both segments compared to RGNNV and SJNNV reference strains. Previously, it has been reported that the reversion of two of these differences (nucleotides 1408 and 1412) in the RNA2 3’NCR to the SJNNV-type (recombinant r1408-1412) resulted in a decrease in sole mortality. In the present study, we have applied an OpenArray^® to analyse the involvement of sole immune response in the virulence of several recombinants: the r1408-1412 and two recombinants, developed in the present study, harbouring mutations at positions 3073 and 3093 of RNA1 3’NCR to revert them to RGNNV-type. According to the correlation values and to the number of expressed genes, the infection with the RNA2-mutant provoked the most different immune response compared to the immune response triggered after the infection with the rest of the viruses, and the exclusive and high upregulation of genes related to the complement system. The infection with the RNA1-mutants also provoked a decrease in mortality and their replication was delayed at least 24 h compared to the wt160 replication, which could provoke the lag observed in the immune response. Furthermore, the infection with the RNA1-mutants provoked the exclusive expression of pkr and the downregulation of il17rc. Full article