Sea Bream Larvae Research Articles

Effects of the dietary supplementation of manganese on growth, skeletal development, oxidative stress and bone metabolism related genes in gilthead seabream (Sparus aurata) larvae

Manganese (Mn) is an essential element necessary for normal growth, antioxidant defense and maintaining bone health. Knowledge about the effects of dietary Mn levels in gilthead seabream (Sparus aurata) larvae performance is still scarce. To determine the effects of dietary Mn levels on growth, survival, skeletal development and expression of antioxidant and bone metabolism related genes, gilthead seabream larvae were fed six experimental microdiets supplemented with manganese sulfate monohydrate (MnSO4.H2O) (contained 6.3, 39, 75, 79, 200 and 270 mg Mn/kg diet). After 26 days of feeding, dietary Mn levels had no effect on larval survival. However, larvae fed the non-supplemented diet (6.3 mg Mn/kg) showed signs of Mn deficiency, including growth reduction, low whole body Mn content, lower expression of mnsod, runx2, oc, and reduced bone mineralization. The poor vertebral body mineralization and low bone relative gene expression in seabream larvae was related to a marked increase in the number of fish with total skeletal anomalies and anomalies of the caudal vertebrae region. On the contrary, larvae fed with Mn supplemented diet up to 270 mg Mn/kg showed increased growth and whole body Mn content, up-regulated mnsod, runx2, alp, opn and oc expression, as well as increased bone mineralization, and reduced number of fish with skeletal anomalies. Therefore, the findings suggest that adequate dietary Mn supplementation positively influences the growth, skeletal development, and antioxidant defense of gilthead seabream larvae, preventing the manifestation of Mn deficiency-related issues.

Transcriptomic Responses and Larval-Stage Growth of Protandrous Yellowfin Seabream (Acanthopagrus Latus) to Different Polyethylene Microplastics Exposure.

Polyethylene microplastics (PE-MPs) were widespread in the marine environment; thus, their influences on marine hermaphroditic fish cannot be ignored. This study intends to evaluate the adverse biological effects of two different sources of PE, identified by Raman spectroscopy, on protandrous yellowfin seabream (Acanthopagrus latus) larvae. Growth retardation, brain lesions, head/body length ratio increase, and neuroendocrine system disorders were found, and growth and neuroendocrine regulation-related genes such as sstr2, ghrb, irs1, UGT2B15, UGT2C1, drd4a, esr2b, hsd3b7, and hsd17b2 were identified. PE microbeads (100 μm) showed more severe tissue damage on fish, while environmental PE fibers (500-2500 μm) showed more imperceptible adverse effects. There were 218 DEGs up-regulated and 147 DEGs down-regulated in the environmental PE group, while 1284 (up) and 1267 (down) DEGs were identified in the virgin PE group. PE-MP stress influenced physiological processes like growth and neuroendocrine regulation and cholesterol-steroid metabolism, and caused tissue damage in the fish larvae. The study highlights the effects of environmental PE exposure on hermaphroditic protandrous fish.

Antioxidant and osteoinductive properties of organic selenium in microdiets for gilthead seabream (Sparus aurata) larvae

This study investigated the effect of yeast derived selenium (Se) dietary supplementation on larval performance, whole body mineral contents, lipid peroxidation, fatty acid profiles, expression of antioxidants and bone biomarkers genes, mineralization and skeletal anomalies in gilthead seabream (Sparus aurata) larvae. Five experimental microdiets containing 1.4, 6.1, 9.2, 12.0 and 14.0 mg Se/kg diets were fed to triplicate groups of larvae (total length: 7.26 ± 0.83 mm, 30 dph) for 21 days. Larval Se levels increased proportionally to the elevation of dietary Se. Those fed with dietary Se level at 6.1 mg/kg had a higher growth performance than those fed with non-supplemented diet (1.4 mg/kg), then reached a plateau from larvae fed with Se6.1 to Se14 diet although growth was not significantly affected by different diets. In addition, larval survival was not significantly affected. However, larvae fed the lowest Se levels showed a significant increase in lipid peroxidation, the downregulation of antioxidant genes, a reduction in polyunsaturated fatty acids (PUFA) contents and the highest incidence of skeletal anomalies. While increase up to 6.1–12 mg Se/kg, reduced oxidative stress, increased PUFA, vertebral mineralization, up-regulated antioxidant and bone metabolism related genes and contributing to reduce skeletal anomalies of larvae. However, further increase in dietary Se up to 14 mg/kg led to the lowest gpx, cat and alp expressions, in agreement with a lower mineralization. These findings suggest, dietary Se level at 6.1 mg/kg would be the minimum dietary Se level required in microdiets for gilthead seabream larvae. Thus, the study demonstrates the importance of dietary Se for bone metabolism and mineralization due to its antioxidant and osteo-inductive properties.

Insights into core molecular changes associated with metamorphosis in gilthead seabream larvae across diverse hatcheries

Early development is a critical period in fish aquaculture and is influenced by biotic and abiotic factors (e.g., temperature, feed) that can vary significantly between hatcheries, making it difficult to identify core factors determining quality. Many of the existing larval transcriptome studies are small-scale and occur under specific rearing conditions that do not mirror the diversity of larviculture practices at an industrial level. In the present transcriptome study, gilthead seabream at the larval to juvenile transition (metamorphosis) from several hatcheries in Europe (Greece, Italy, and France) were analysed in a large-scale RNA-seq study. The aim was to uncover the most significant molecular modifications occurring during metamorphosis, irrespective of differences in biotic or abiotic factors, to address knowledge gaps associated with critical early developmental stages under industrial hatchery conditions. Commonly modified gene transcripts between larval stages were identified based on the clustering of gene expression profiles of 25 gilthead seabream libraries from different hatcheries in a PCA analysis. When larvae at flexion were compared to larvae at mid-metamorphosis, 2243 differentially expressed genes (DEGs) were identified, and when larvae at early to mid-metamorphosis were compared to mid to late-metamorphosis, 2299 DEGs were identified. Comparative analysis across the developmental stages of gilthead seabream revealed genes of importance for the metamorphic transition and adaptation to rearing conditions, including genes related to the nervous system at flexion (24 days post hatch), enteroendocrine cell differentiation, and lipid homeostasis at early to mid-metamorphosis (46 dph), and enrichment of genes indicative of immune competence at mid to late-metamorphosis (51–54 dph). The differential expression of some endocrine-associated genes, dio1, dio2, cldn1, ing4, Pou3f4, and fgf22, highlights their importance in metamorphosis. Meta-analysis of the transcriptomes from two species, the gilthead seabream and Senegalese sole, that have differing symmetry and ecology uncovered common molecular expression patterns that underlie larvae maturation during metamorphosis, and we propose that these represent core gene markers of metamorphosis in these two fish species.

Effects of selenium nanoparticles on larval development, ontogeny of antioxidant enzymes and fatty acid profile in Arabian yellowfin seabream (Acanthopagrus arabicus)

Selenium (Se) is an essential trace element that has vital effects on growth, antioxidant capacity and early development in marine fish larvae. However, traditional livefoods such as rotifer and artemia lack of Se. In this regard, a 50-day feeding experiment was conducted in order to examine the effects of Rotifer and Artemia enrichment with selenium nanoparticles (SeNPs) on growth, antioxidant capacity and fatty acid profile of Arabian yellowfin seabream (Acanthopagrus arabicus) larvae. Four levels of SeNPs were used to prepare the experimental emulsions,including control (0), 0.5, 1.0 and 5 mg SeNPs L−1. Larvae were stocked at density of 50 larvae L−1 into twelve 250-L cylindrical tanks. Tanks supplied with seawater (23 ± 1 ºC; 40.0 ± 1.0 g L−1). Green water was used from day first until 20 days after hatch (DAH). Rotifers (15 ml−1) were offered to larvae from day 2–21 DAH and Artemia metanauplii (1–3 Artemia ml−1) were offered to larvae from day 18–45 DAH. Fish were sampled at 0, 7, 10, 15, 22, 30, 40, 45, 50 DAH. The Se concentration in the livefoods and larval whole body linearly increased with the increment of SeNPs level in the experimental emulsions. Larvae wet weight showed quadratic response and increased with SeNPs up to 1 mg mg SeNPs/L, then decreased in SeNPs (5.0) group. The activity of antioxidant enzymes including catalase, superoxide dismutase glutathione peroxidase, and total antioxidant capacity increased but malondialdehyde level decreased in larvae fed the SeNPs-enriched livefoods and showed both linear and quadratic responses. Lysozyme activity in the whole body of larvae fed SeNPs-enriched livefoods had both linear and quadratic responses and in the most of the sampling times was higher than the control group. Docosahexaenoic acid (DHA) level in the livefoods and larval whole body increased with SeNPs. In conclusion, livefoods enrichment with SeNPs at 1 mg L−1 is recommended to elevate the antioxidant capacity and non-specific immune response in A. arabicus larvae.

Virulence and pangenome analysis of Vibrio harveyi strains from Greek and Red Sea marine aquaculture

Comparative genomic analysis of Vibrio harveyi, a leading pathogen in Mediterranean aquaculture, was conducted to assess the genomic plasticity of the species. V. harveyi is responsible for vibriosis outbreaks during the warmer months, resulting in significant economic losses that impact Greek aquaculture. Over a span of six years, we curated a diverse collection of bacterial strains associated with these outbreaks. Whole-genome sequencing was employed in 21 strains to uncover their evolutionary relationships and virulence factors. Pangenome analysis revealed significant gene gain/loss, with numerous unique genes within the strains. The core genome featured genes associated with pathogenicity, including secretion systems, flagella, pili, siderophores, and toxins. Furthermore, we examined the phenotypic traits and virulence of these strains using in vivo testing with gilthead seabream larvae. Our findings indicated variant metabolic profiles and virulence among the strains during these in vivo assays. By integrating genomic and phenotypic data, our study highlights the ongoing evolution of disease-associated V. harveyi strains, which pose a growing challenge to the aquaculture industry.

Skeletal anomalies in gilthead seabream (Sparus aurata) larvae reared in different densities and water volumes

AbstractThis study describes the effects on the skeletal phenotype of two pivotal factors, density and water volume, don the hatchery (larval) phase of gilthead seabream (Sparus aurata) larvae previoulsy described for two model species (Danio rerio and Oryzias latipes) and sub‐adult (pre‐ongrowing) gilthead seabream (Sparus aurata). The experimental trial was conducted using single conditions in a pilot study, starting with a total of 615,385 eggs from the same batch. Three densities (LD low density: 25 larvae/L; MD medium density: 125 larvae/L; and HD high density: 250 larvae/L) and two water volumes (500 and 1000 L) were tested from spawning up to 60 days post‐hatching (dph) (average standard length: 1.79 cm; average dry weight: 27.11 mg). On the final samples, morphometric, anatomical, and histological data were collected for data pertinent to meristic counts and skeletal anomalies. The results (analyzed by means of multivariate analyses) indicated that the LD‐reared larvae were significantly longer and heavier than HD‐reared fish. Furthermore, LD‐reared gilthead seabream exhibited a significant reduction in the frequency of individuals with anomalies of jaws, vertebral body shape, and vertebral arches than the MD and HD conditions, which is in agreement with previous experiments carried out on model species and gilthead seabream sub‐adults.

Bacterial community structures and dynamics associated with rotated positioning syndrome in gilthead sea bream (Sparus aurata) larviculture

IntroductionThe availability of high-quality gilthead seabream (Sparus aurata) larvae in larviculture represents a major bottleneck to the aquaculture. This challenge can be compounded by losses resulting from the emergence of a clinical disorder’s symptomatology. In this study, the observed syndrome included a rotated positioning of the larval sagittal plane and in most cases leading eventually to death. MethodsHerein, we examined using amplicon sequencing of the 16S rDNA the bacterial communities associated with S. aurata larvae at different conditions (including both fish with no evidence of the syndrome and fish with syndrome) during the early developmental stages along with the contribution of rearing water, organic matter and provided feed in the microbiota during an experiment of 18 days. ResultsOver the development of larvae, differences were observed in the bacterial composition between healthy and symptomatic larvae as well as between components of the system. A remarkable presence of members of the Psychrobacter genus was observed in symptomatic larvae with a significant increase at 18dph. The healthy larvae harbor different bacterial profile with a dominance of Vibrio and Bacillus genera during 3-8dph, various members of Alphaproteobacteria during 11-14dph and Marinifilum at 18dph. The rearing water showed a different bacterial profile compared to the other components, with a slight effect of healthy larvae at 3-8dph. The bacteriome of feeds provided during the rearing of larvae was found to be diverse. Chlorella was mainly dominated by members of Firmicutes, while Rotifer and Artemia were mainly dominated by members of Proteobacteria including different species of Psychrobacter. At 18dph, Artemia feed seems to affect the symptomatic larvae bacteriome, where it enhanced the presence of Psychrobacter spp.DiscussionInterestingly, the comparative network analysis at 18dph indicated that the bacterial associations in symptomatic larvae were primarily driven by members of the Psychrobacter genus. While various phyla contributed to bacterial associations in healthy larvae with different frequencies including mainly members of Proteobacteria, Bacteroidota and Firmicutes phyla. Finally, the Gammaproteobacteria/Alphaproteobacteria ratio was found to be related to the health condition of larvae. This study provides valuable information which can be used as indicators for monitoring the health status of S. aurata larvae.

Enrichment of live foods with arachidonic acid enhanced stress resistance, digestive enzyme activity, and total antioxidant capacity in yellowfin seabream (Acanthopagrus latus) larvae

Enrichment of live foods with arachidonic acid enhanced stress resistance, digestive enzyme activity, and total antioxidant capacity in yellowfin seabream (Acanthopagrus latus) larvae

Polyinfection in Fish Aeromoniasis: A Study of Co-Isolated Aeromonas Species in Aeromonas veronii Outbreaks.

We studied the phenotypic and genomic characteristics related to the virulence and antibiotic resistance of two Aeromonas strains, which were co-isolated before an outbreak of Aeromonas veronii among diseased seabass on Agathonisi Island, Greece, in April 2015. The first strain, AG2.13.2, is a potentially pathogenic mesophilic variant of Aeromonas salmonicida, and the second, AG2.13.5, corresponds to an Aeromonas rivipollensis related to A. rivipollensis KN-Mc-11N1 with an ANI value of 97.32%. AG2.13.2 lacks the type III secretion system just like other mesophilic strains of A. salmonicida. This characteristic has been associated with lower virulence. However, the genome of AG2.13.2 contains other important virulence factors such as type II and type VI secretion systems, and toxins such as rtxA, aerolysin aer/act, and different types of hemolysins. The strain also carries several genes associated with antibiotic resistance such as the tetE efflux pump, and exhibits resistance to tetracycline, ampicillin, and oxolinic acid. In an in vivo challenge test with gilthead seabream larvae, the A. veronii bv sobria strain AG5.28.6 exhibited the highest virulence among all tested strains. Conversely, both A. salmonicida and A. rivipollensis showed minimal virulence when administered alone. Interestingly, when A. veronii bv sobria AG5.28.6 was co-administered with A. rivipollensis, the larvae survival probability increased compared to those exposed to A. veronii bv sobria AG5.28.6 alone. This finding indicates an antagonistic interaction between A. veronii bv sobria AG5.28.6 and A. rivipollensis AG2.13.5. The co-administration of A. veronii bv sobria AG5.28.6 with Aeromonas salmonicida did not yield distinct survival probabilities. Our results validate that the primary pathogen responsible for European seabass aeromoniasis is Aeromonas veronii bv sobria.

Genomics goes deeper in fisheries science: The case of the blackspot seabream (Pagellus bogaraveo) in the northeast Atlantic

Recent advances in genomics are an essential contributor to the assessment of fish stocks by providing a fine-scale identification of the species' genetic boundaries. The blackspot seabream, Pagellus bogaraveo, is a commercial sparid distributed across the northeast (NE) Atlantic and the Mediterranean. Within the NE Atlantic, three P. bogaraveo stocks are currently defined: Azores; Atlantic Iberian waters; Celtic Sea and the Bay of Biscay. We used a genotyping-by-sequencing (GBS) approach to better define the spatial scale at which the species occurs in the NE Atlantic. Our findings revealed the existence of an additional genetic cluster in the eastern Atlantic (Gulf of Cádiz) that was not identified in previous studies based on mitochondrial DNA or microsatellite data. The combined effect of ocean circulation patterns, complex bathymetry and the existence of local upwelling may play an important role on the retention of blackspot seabream larvae and adults, providing an explanation for the genetic differentiation between the specimens caught off the Gulf of Cádiz and Peniche (Portugal). Results presented here revealed hidden intra-specific genetic differentiation and can inform a finer-scale sampling to determine the new stock boundaries in the Atlantic Iberian coasts.

The effect of delayed first feeding on growth and survival of yellowfin seabream (Acanthopagrus arabicus) larvae

The effect of different initial feeding times (48 h, 72 h, 96 h, and 120 h after hatching) and food deprivation on the point-of-no-return (PNR), survival, and growth of yellowfin seabream Acanthopagrus arabicus larvae were studied under controlled condition. Growth parameters were investigated by evaluating morphometric (head depth, body depth, gut height, musculature height, eye diameter, total length, yolk, and oil globule volume) and gravimetric (dry weight) indices. The larvae commenced to feed exogenously at the mouth opening stage on day 2 after hatching (DAH) and reached PNR between 6 and 7 DAH at 19–20 °C. The time of initial feeding significantly affected the larval growth. From 3 DAH until the end of the trial period at 15 DAH, the growth (all morphometric indices and dry weight) of larvae started which earlier initial feeding start (48 h and 72 h after hatching) were significantly higher than that of 96 h (P < 0.05). Growth parameters were measured until 9 DAH in the larvae commenced feeding at 120 h, since complete mortality was recorded after this sampling point (at 12 DAH). During this period, the larvae showed significantly lower morphometric indices and dry weight compared with larvae in other initial feeding time treatments (48 h, 72 h, and 96 h). Yolk absorption in yellowfin seabream larvae was completed on 4 DAH regardless of the variances in the time of first feeding. Likewise, the oil globule was completely utilized on 5 DAH in all initial feeding trials. No significant differences were noticed in yolk volume and oil globule absorption between different treatments. At the end of the trial at 15 DAH, the survival rate was significantly higher for larvae began first feeding at 48 h (35.67 ± 7.01%) and 72 h (36.48 ± 4.72%) when compared to 96 h first feeding larvae (13.10 ± 2.62%)(P < 0.05). The findings from the current study reveal that the first feeding of yellowfin seabream larvae can be initiated up to 72 h after hatching with no significant differences in growth and survival rate.

Core microbiome profiles and their modification by environmental, biological, and rearing factors in aquaculture hatcheries

16S rRNA gene sequencing and bacteria- and genus-specific quantitative PCR was used to profile microbial communities and their associated functions in water, live feed (microalgae, Artemia, and rotifer), and European sea bass and gilthead sea bream larvae from hatcheries in Greece and Italy. The transfer to larvae of genus containing potential pathogens of fish was more likely with Artemia and rotifer than with microalgae or water, irrespective of geographic location. The presence of potentially pathogenic bacteria (Vibrio and Pseudoalteromonas) in the core microbiota of water, live feed, and fish larvae, the enrichment of different bacterial resistance pathways and biofilm formation, and the overall low beneficial bacteria load during larval ontogeny emphasizes the risk for disease outbreaks. The present data characterizing microbiota in commercial aquaculture hatcheries provides a baseline for the design of strategies to manage disease and to model or remediate potential adverse environmental impacts.

The effect of dietary docosahexaenoic acid (DHA; 22:6n-3) on photoreceptor abundance, rhodopsin expression and growth in developing gilthead sea bream (Sparus aurata) larvae

This study determined the effect of prey DHA on larval gilthead sea bream (GSB; Sparus aurata) photoreceptor abundance, rhodopsin expression, and growth performance. It was carried out in a twenty-eight 400 l conical tank system that was stocked with 100 viable GSB eggs/l/tank. This allowed the testing of 4 levels of rotifer DHA; 0.99 (Low; L), 1.9 (Intermediate low; I-L), 3.2 (Intermediate high; I-H) and 12.1(High; H) mg DHA/g DW rotifer, which were fed (10 rotifers/ml) to 3-16 DPH larvae. These rotifer diets continued to be offered to 17-34 DPH fish, although these larvae predominantly fed on 4 DHA enriched Artemia nauplii treatments that were offered at a concentration from 0.1 nauplii/ml to 4 nauplii/ml, depending on larval age. This resulted in 4 DHA rotifer-Artemia ranges: 0.99-0.0 (L), 1.9-2.6 (I-L), 3.2-7.2 (I-H), and 12.1-11.77 (H) mg DHA/g DW. The 4 DHA treatments and ranges were tested in replicates of 7 conical tanks per treatment. Increasing rotifer DHA significantly (P&lt;0.0001) improved TL, in an exponential manner, throughout larval rearing. DW in 34 DPH larvae was markedly (P&lt;0.05) enhanced with dietary DHA inclusion in the rotifers and Artemia. There was a significant (P &lt; 0.005) prey DHA dose dependent range effect on the abundance of photoreceptor cells in the retina of 34 DPH larvae. The gene expression of rhodopsin in GSB larvae was significantly (P&lt;0.05) upregulated with dietary DHA dose range and larval age (P&lt;0.0001). This study established a link between dietary DHA level with photoreceptor abundance and rhodopsin expression, which led to improved vision, prey acquisition, and growth in developing GSB larvae.

Interaction between Dietary Vitamin D3 and Vitamin K3 in Gilthead Seabream Larvae (Sparus aurata) in Relation to Growth and Expression of Bone Development-Related Genes.

Vitamins D and K are essential fat-soluble nutrients that intervene in bone development processes among other biological functions. The present study is aimed at investigating the potential combined effect of dietary supplementation with vitamin D3 (cholecalciferol) and vitamin K3 (menadione) in gilthead seabream (Sparus aurata) larvae. For that purpose, seabream diets were supplemented with different combinations of vitamin D3/vitamin K3 (mg/kg diet) as follows: 0.00/0, 0.06/70, 0.06/170, 0.13/70, 0.13/170, 0.40/70, and 0.40/170. Feeding gilthead seabream larvae (22 days post hatch) for 21 days with the diets supplemented with 0.06-0.13 mg/kg vitamin D3 and 70 mg/kg vitamin K3 (diets 0.06/70 and 0.13/70) led to the highest larval growth and survival and the highest expression of important biomarkers of both bone development and health, such as bmp2, osx, and mgp, and calcium homeostasis, such as pthrp and casr. However, the increased supplementation with both vitamins at 0.40 mg/kg vitamin D3 and 170 mg/kg vitamin K3 (diet 0.40/170) reduced larval growth and survival, downregulated bmp2 and pthrp expressions, and upregulated osx and mgp, causing an unbalance in the relative expression of these genes. The results of the present study have shown the interaction between vitamin D3 supplementation and vitamin K3 supplementation in larval performance and gene expression related to bone development and calcium homeostasis, denoting the significance of a correct balance between both vitamins in larval diets.

Deficiency and excess in dietary vitamin K3 negatively affect gilthead seabream (Sparus aurata) larvae performance and bone health

Despite the importance of vitamin K to maintaining normal growth, survival, and bone health in fish, studies on the effect of different dietary levels of vitamin K on marine fish larvae are very scarce. In the present study, the effect of vitamin K on growth performance, incidence of bone anomalies, bone mineralization, and expression of bone biomarkers were investigated in gilthead seabream larvae by feeding microdiets with six different levels of vitamin K3 (1.32, 1.63, 4.98, 12.26, 22.90, and 58.51 mg kg−1) for 14 days. The highest total length and body weight were registered in larvae fed 4.98 mg kg−1 vitamin K3, whereas the further increase in dietary vitamin K3 up to 22.9 and 58.51 mg kg−1 reduced growth and survival. The highest incidence of anomalies in branchiostegal rays, glossohyal, or neurocranium bones was found in larvae fed the lowest vitamin K3 level (1.32 mg kg−1), whereas the increase in vitamin K3 reduced these anomalies following potential regressions with inflection points close to 5 mg kg−1 vitamin K3. However, larvae fed the highest vitamin K3 levels (22.9 and 58.51 mg kg−1) showed a high incidence of abdominal kyphosis, reduced mineralization, and unbalances in the expression of bone health-related genes. In conclusion, the present study suggested an optimum dietary level of 5 mg kg−1 of vitamin K3 to promote seabream larval growth and reduce the incidence of bone anomalies. On the contrary, the elevation of dietary vitamin K3 levels up to 22.9 and 58.51 mg kg−1 has a deleterious effect on larval performance and bone health.

Comprehensive Characterization of a Novel Bacteriophage, vB_VhaS_MAG7 against a Fish Pathogenic Strain of Vibrio harveyi and Its In Vivo Efficacy in Phage Therapy Trials.

Vibrio harveyi, a significant opportunistic marine pathogen, has been a challenge to the aquaculture industry, leading to severe economical and production losses. Phage therapy has been an auspicious approach in controlling such bacterial infections in the era of antimicrobial resistance. In this study, we isolated and fully characterized a novel strain-specific phage, vB_VhaS_MAG7, which infects V. harveyi MM46, and tested its efficacy as a therapeutic agent in challenged gilthead seabream larvae. vB_VhaS_MAG7 is a tailed bacteriophage with a double-stranded DNA of 49,315 bp. No genes linked with virulence or antibiotic resistance were harbored in the genome. The phage had a remarkably large burst size of 1393 PFU cell-1 and showed strong lytic ability in in vitro assays. When applied in phage therapy trials in challenged gilthead seabream larvae, vB_VhaS_MAG7 was capable of improving the survival of the larvae up to 20%. Due to its distinct features and safety, vB_VhaS_MAG7 is considered a suitable candidate for applied phage therapy.

Changes of oxidative status in yellowfin seabream larvae (Acanthopagrus latus) during development

Dynamic changes of tissues, organs and growth that occur in fish larvae during the transition to the juvenile stage are accompanied by differences in metabolic, locomotor and feeding activities that can reflect on fish's oxidative status. In this study, we examine how body growth, antioxidant system (superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR) and total antioxidant capacity (TAC) and oxidative damage (malondialdehyde-MDA) parameters change in larvae of yellowfin seabream larvae (Acanthopagrus latus) during early development (0, 7, 15, 22 and 30 day after hatching-DAH). Body growth (length and weight) starts to intensify from 15 DAH. We observed general increase in the antioxidant system (AOS) with the age of larvae from newly hatched and 7 DAH up to 15 and 22 DAH individuals. 15 and 22 DAH larvae had the greatest levels of TAC, SOD and GR activity, while 30 DAH larvae had higher CAT activity from 0, 7 and 15 DAH and MDA concentration in comparison to 15 DAH individuals. Several developmental events can be linked with observed results: lower AOS in 0 and 7 DAH individuals with low locomotor activity, growth, endo-exogenous feeding phase and cell differentiation; 15 and 22 DAH larvae are under pressure of fast growth, enhanced swimming and foraging capacity; while higher MDA production in 30 DAH larvae can be a result of shifts in muscle metabolism, changes in both quality and quantity of food and a significant increase in weight. The present study provides insight into the changes in redox status during the ontogeny of A. latus, fish species about which physiology is still little known but with a potential for use in marine culture. Ability to lower oxidative stress during critical developmental periods can enhance that potential.

Viral nervous necrosis resistance in gilthead sea bream (Sparus aurata) at the larval stage: heritability and accuracy of genomic prediction with different training and testing settings

BackgroundThe gilthead sea bream (Sparus aurata) has long been considered resistant to viral nervous necrosis (VNN), until recently, when significant mortalities caused by a reassortant nervous necrosis virus (NNV) strain were reported. Selective breeding to enhance resistance against NNV might be a preventive action. In this study, 972 sea bream larvae were subjected to a NNV challenge test and the symptomatology was recorded. All the experimental fish and their parents were genotyped using a genome-wide single nucleotide polymorphism (SNP) array consisting of over 26,000 markers.ResultsEstimates of pedigree-based and genomic heritabilities of VNN symptomatology were consistent with each other (0.21, highest posterior density interval at 95% (HPD95%): 0.1–0.4; 0.19, HPD95%: 0.1–0.3, respectively). The genome-wide association study suggested one genomic region, i.e., in linkage group (LG) 23 that might be involved in sea bream VNN resistance, although it was far from the genome-wide significance threshold. The accuracies (r) of the predicted estimated breeding values (EBV) provided by three Bayesian genomic regression models (Bayes B, Bayes C, and Ridge Regression) were consistent and on average were equal to 0.90 when assessed in a set of cross-validation (CV) procedures. When genomic relationships between training and testing sets were minimized, accuracy decreased greatly (r = 0.53 for a validation based on genomic clustering, r = 0.12 for a validation based on a leave-one-family-out approach focused on the parents of the challenged fish). Classification of the phenotype using the genomic predictions of the phenotype or using the genomic predictions of the pedigree-based, all data included, EBV as classifiers was moderately accurate (area under the ROC curve 0.60 and 0.66, respectively).ConclusionsThe estimate of the heritability for VNN symptomatology indicates that it is feasible to implement selective breeding programs for increased resistance to VNN of sea bream larvae/juveniles. Exploiting genomic information offers the opportunity of developing prediction tools for VNN resistance, and genomic models can be trained on EBV using all data or phenotypes, with minimal differences in classification performance of the trait phenotype. In a long-term view, the weakening of the genomic ties between animals in the training and test sets leads to decreased genomic prediction accuracies, thus periodical update of the reference population with new data is mandatory.

Effects of the dietary supplementation of copper on growth, oxidative stress, fatty acid profile and skeletal development in gilthead seabream (Sparus aurata) larvae

The effect of dietary copper (Cu) levels on growth, oxidative stress, fatty acid profile and bone health of gilthead seabream larvae (Sparus aurata) was studied in 47 days-post-hatching fish fed 4 experimental diets containing 17, 18, 19 and 25 mg Cu/kg diet. After 21 days of feeding, larval growth and survival were not affected by the dietary Cu levels. However, larvae fed the non-supplemented diet (17 mg Cu/kg) showed clear symptoms of Cu deficiency, including increased lipid peroxidation and reduced bone mineralization. Increased peroxidation risk caused a reduction in essential fatty acids and n-3 PUFA (polyunsaturated fatty acids) contents in whole body lipids, whereas the poor vertebral body mineralization in seabream larvae was related to a marked increase in abdominal vertebrae anomalies. On the contrary, dietary Cu supplementation raised whole-body contents in DHA, EPA and n-3 PUFA and reduced MUFA, TBARS and the incidence of severe, cranial, branchiostegal rays and abdominal vertebral anomalies. Polynomial regression models applied to all these parameters suggested optimum dietary Cu levels to be 21.5–22.6 mg/kg in gilthead seabream larvae microdiets supplemented with CuSO4.5H2O. These levels (21.5–22.6 mg/kg) are in the range of the Cu contents in copepods (12–38 mg/kg) and on the verge of the dietary levels authorized by EU Commission in feeds for cultured fish species (25 mg Cu/kg diet).