Aroclor 1254 inhibits vasotocinergic pathways related to osmoregulatory and stress functions in the gilthead sea bream (Sparus aurata, Linnaeus 1758)

The present study assesses the response of vasotocinergic system in the gilthead sea bream (Sparus aurata) after administering two doses of the polychlorinated biphenyl Aroclor 1254 (15 or 50 μg g^-1 fresh body mass). Seven days post-administration, eight fish of each experimental group were sampled, and the remaining animals were challenged with a hyperosmotic stress by being transferred from seawater (36 ppt) to high salinity water (55 ppt) and being sampled 3 days post-transfer. Aroclor 1254 affected gene expression of avt, together with Avt concentrations in pituitary and plasma, inhibiting the stimulation observed in vasotocinergic system after hyperosmotic challenge. This was noted by the accumulation of Avt at hypophyseal level as well as by its undetectable values in plasma. Hyperosmotic transfer significantly changed branchial avtrv1a, avtrv2, atp1a and cftr mRNA expression levels in control fish, while in Aroclor 1254-treated fish they remained mostly unchanged. This desensitization also occurred for avtrs in hypothalamus, caudal kidney and liver. In addition, an enhancement in plasma cortisol concentration, together with the orchestration of several players of the Hypothalamic-Pituitary-Interrenal axis (crh, crhbp, trh, star), was also observed mostly at the highest dose used (50 μg g^-1 body mass), affecting plasma and hepatic metabolites. Our results demonstrated that Aroclor 1254 compromises the hypoosmoregulatory function of vasotocinergic system in S. aurata, also inducing a concomitant stress response. In summary, this study demonstrates that Aroclor 1254 can be considered an important endocrine disruptor in relation with the correct arrangement of vasotocinergic, metabolic and stress pathways after their stimulation by transfer to hyperosmotic environments.

Artemia spp., a Susceptible Host and Vector for Lymphocystis Disease Virus

Different developmental stages of Artemia spp. (metanauplii, juveniles and adults) were bath-challenged with two isolates of the Lymphocystis disease virus (LCDV), namely, LCDV SA25 (belonging to the species Lymphocystis disease virus 3) and ATCC VR-342 (an unclassified member of the genus Lymphocystivirus). Viral quantification and gene expression were analyzed by qPCR at different times post-inoculation (pi). In addition, infectious titres were determined at 8 dpi by integrated cell culture (ICC)-RT-PCR, an assay that detects viral mRNA in inoculated cell cultures. In LCDV-challenged Artemia, the viral load increased by 2–3 orders of magnitude (depending on developmental stage and viral isolate) during the first 8–12 dpi, with viral titres up to 2.3 × 10² Most Probable Number of Infectious Units (MPNIU)/mg. Viral transcripts were detected in the infected Artemia, relative expression values showed a similar temporal evolution in the different experimental groups. Moreover, gilthead seabream (Sparus aurata) fingerlings were challenged by feeding on LCDV-infected metanauplii. Although no Lymphocystis symptoms were observed in the fish, the number of viral DNA copies was significantly higher at the end of the experimental trial and major capsid protein (mcp) gene expression was consistently detected. The results obtained support that LCDV infects Artemia spp., establishing an asymptomatic productive infection at least under the experimental conditions tested, and that the infected metanauplii are a vector for LCDV transmission to gilthead seabream.

Transport and Recovery of Gilthead Seabream (Sparus aurata L.) Sedated With Clove Oil and MS-222: Effects on Stress Axis Regulation and Intermediary Metabolism

Transport processes between aquaculture facilities activate the stress response in fish. To deal with these situations, the hypothalamic-pituitary-interrenal (HPI) axis releases cortisol, leading to an increase in circulating energy resources to restore homeostasis. However, if the allostatic load generated exceeds fish tolerance limits, stress-related responses will compromise health and welfare of the animals. In this context, anesthetics have arisen as potential agents aiming to reduce negative effects of stress response. Here we assessed the effects of a sedative dose of clove oil (CO) and MS-222 on hallmarks involved in HPI axis regulation and energy management after simulated transport, and further recovery, in gilthead seabream (Sparus aurata L.) juveniles. Fish were placed in a mobile setup of water tanks where transport conditions were simulated for 6 h. Sedation doses of either CO (2.5 mg L⁻¹) or MS-222 (5 mg L⁻¹) were added in the water tanks. A control group without anesthetics was also included in the setup. Half of the animals (n = 12 per group) were sampled immediately after transport, while remaining animals were allowed to recover for 18 h in clean water tanks and then sampled. Our results showed that the HPI axis response was modified at peripheral level, with differences depending on the anesthetic employed. Head kidney gene-expressions related to cortisol production (star and cyp11b1) matched concomitantly with increased plasma cortisol levels immediately after transport in CO-sedated fish, but these levels remained constant in MS-222-sedated fish. Differential changes in the energy management of carbohydrates, lipids and amino acids, depending on the anesthetic employed, were also observed. The use of CO stimulated amino acids catabolism, while MS-222-sedated fish tended to consume liver glycogen and mobilize triglycerides. Further studies, including alternative doses of both anestethics, as well as the assessment of time-course HPI activation and longer recovery periods, are necessary to better understand if the use of clove oil and MS-222 is beneficial for S. aurata under these circumstances.

Biochemical impacts in adult and juvenile farmed European seabass and gilthead seabream from semi-intensive aquaculture of southern European estuarine systems

The nutritional value and developmental variations of cultured fish were assessed for European seabass and gilthead seabream specimens reared in semi-intensive aquaculture systems in two Portuguese estuaries. Quantification of total protein and of carbohydrate and fatty acid profiles was carried out to determine differences between the composition of the same species in two development stages reared in four distinct farms. A significant influence of the rearing site on the nutritional composition of the same species was found for adult European seabass regarding saturated, monounsaturated and highly unsaturated fatty acids contents, both between estuaries and within each estuary. In gilthead seabream, saturated, monounsaturated, polyunsaturated and highly unsaturated fatty acids content were also influenced by the rearing site. Carbohydrate analysis showed a significant influence of the rearing site on free sugar and polysaccharide content in fish of both species, and there was no influence on the species' protein content. Differences in fatty acid and carbohydrate content among juvenile and adult stages were found for all the groups studied. The present study supported the existing evidence that semi-intensive rearing systems are subjected to the variability of extrinsic factors in the rearing sites, influencing the nutritional value of the same species, namely regarding lipid and carbohydrate profiles, depending on the production site. From a consumer's perspective, such differences may come as a disadvantage of the rearing method, as it is expected for a product to provide equal nutritional properties and benefits regardless its origin, especially within the same country.

Histopathological effects in gills and liver of Sparus aurata following acute and chronic exposures to erythromycin and oxytetracycline

Due to their worldwide use and environmental persistence, antibiotics are frequently detected in various aquatic compartments. Their toxic properties raise environmental concerns to non-target organisms. Histopathology data is frequently applied in ecotoxicology studies to assess the effects of different classes of environmental stressors in fish, including antibiotics. Tissue alterations in gills and liver of gilthead seabream (Sparus aurata) individuals acutely (96 h) and chronically (28 days) exposed to environmentally relevant concentrations of the antibiotics erythromycin (ERY: 0.0002-200 μg/L) and oxytetracycline (OTC: 0.0004-400 μg/L), including a control non-exposed group, were evaluated. Several disorders (circulatory, regressive, progressive, and inflammatory) were observed in both organs of all exposed animals. The hereby obtained data showed a higher and significant increase in gill histopathological index of organisms acutely exposed to ERY and of those chronically exposed to OTC. In terms of categorical lesions, only a significant increase of regressive and progressive alterations occurred in gills after chronic exposure to OTC. For the liver, a significant increase in pathological index was also detected, as well as regressive changes, after chronic exposure to OTC. Furthermore, the present study indicates that most of the changes observed in gills and liver were of mild to moderate severity, which might be adaptive or protective, non-specific, and mostly reversible. Despite being observed, irreversible lesions were not significant in any of the fish organs analyzed. Although there were histological changes, gill apparatus was considered still functionally normal, as well as liver tissue, not supporting the occurrence of severe toxicity. In general, the observed histological changes were not stressor-specific, and toxicological mechanistic explanations for the alterations observed in gills and liver are presented. The obtained data showed that histopathological biomarkers can be successfully applied in ecotoxicological studies, evidencing their relevance, responsivity, and complementarity to other biochemical biomarker-based approaches.

Production and Refinement of Omega-3 Rich Oils from Processing By-Products of Farmed Fish Species

In this study, the effect of a four-stage chemical refining process (degumming, neutralization, bleaching, deodorization) on the quality parameters, fatty acid composition and volatile compounds of crude oils produced from processing by-products of farmed fish species (tuna, seabass and gilthead seabream) was evaluated. The quality of the oils was compared to commercially available cod liver oil on the basis of free fatty acid, peroxide value, p-anisidine, total oxidation (TOTOX), thiobarbituric acid reactive species (TBARS), oxidative stability at 80, 100 and 120 °C, tocopherol content, and volatile components, while the fatty acid profile and the proportion of polyunsaturated fatty acids (PUFAs) were used as an indicator of the nutritional values of fish oils. Quality parameters of the studied oils and oil oxidative stability were enhanced with refining and were within the limits recommended for fish oils without the loss of PUFAs. In tuna by-product refined oils, the proportion of PUFAs was over 40%, with 30% of eicosapentaenoic and docosahexaenoic fatty acids. The volatile compounds of the oils were quantified (in mg/kg) and major components were 2,4-heptadienal, pentadecane, 2,4-decadienal, 2,4-nonadienal and dodecane. The use of aquaculture by-products as an alternative source for fish oil production could contribute to a more sustainable and profitable aquaculture production, providing economic benefits for the producers and setting new standards for a fish by-product disposal strategy.

Arginine Vasotocin and Cortisol Co-regulate Vasotocinergic, Isotocinergic, Stress, and Thyroid Pathways in the Gilthead Sea Bream (Sparus aurata)

In teleosts, a complex interaction between several endocrine axes modulates physiological functions related to metabolism, stress, and osmoregulation. Although many studies in fish underline the interconnection between the hypothalamic–pituitary–interrenal (HPI) and hypothalamic–pituitary–thyroid (HPT) endocrine axes, their relationship with the vasotocinergic and isotocinergic systems remains unknown. The aim of the present study is therefore to shed light on the potential cross-regulations between HPT, HPI, and the vasotocinergic and isotocinergic axes in gilthead sea bream (Sparus aurata) at hypothalamic, hypophyseal, and plasma levels. Sea breams were administered with intraperitoneal slow-release implants containing different doses of vasotocin (the active peptide in vasotocinergic system) or cortisol (the last component of HPI axis). Plasma osmolality was higher in active neuropeptides vasotocin (Avt)-treated fish, indicating an osmoregulatory function of this hormone. Low concentrations of Avt increased hypothalamic arginine vasotocin precursor (avt) mRNA levels and increased Avt storage in the pituitary. Avt treatment down-regulated hypothalamic arginine vasotocin receptor v1a-type (avtrv1a), suggesting a negative paracrine co-regulation of the HPI axis due to the close location of avtrv1a and adrenocorticotropin hormone (Acth) cells in the anterior pituitary. Furthermore, the up-regulation observed in arginine vasotocin receptor v2-type (avtrv2) suggests their involvement in metabolic and cortisol-related pathways in the hypothalamus. The decrease in isotocin (It) pituitary storage and the up-regulation of it receptor, observed in the Avt-treated group, reinforce the idea of an interconnection between the vasotocinergic and isotocinergic systems. Cortisol and Avt administration each inhibited the HPI axis, down-regulating crh gene expression in the absence of variations in corticotropin releasing hormone binding protein (crhbp). Finally, both hormonal treatments activated the HPT axis via up-regulation of trh and down-regulation of thrb. Our results provide evidence for strong interactions among the Avt/It, HPI, and HPT axes of marine teleosts, particularly at the hypothalamic level.

The genetic population structure and temporal genetic stability of gilthead sea bream Sparus aurata populations in the Aegean and Ionian Seas, using microsatellite DNA markers

We examined 662 gilthead sea bream Sparus aurata from wild samples of the species in the Aegean and Ionian Seas, using 20 EST-linked microsatellite markers, in three multiplex panels, as well as seven anonymous loci. Most of the markers were revealed to be highly polymorphic. We found low genetic differentiation between the sampling stations/areas with total F_ST 0.002 (P < 0.05). Based on comparison of five temporal samples, our results indicate genetic data consistency over time for all tested samples, pointing to stable populations, despite reported repeated escape events. Our results confirm the genetic population structure previously observed in these specific areas, using by far more markers than in previous studies in both coding and non-coding DNA loci. The limited genetic structure and the temporal genetic stability indicate neither major genetic differentiation of local populations by geographic isolation nor influence from anthropogenic factors. These results provide a baseline for future reference in any management programme of both wild and farmed population of S. aurata as well as of other aquaculture species with a potential introgression among farmed and wild populations.

A long-term growth hormone treatment stimulates growth and lipolysis in gilthead sea bream juveniles

The enhancement of the endocrine growth hormone (GH)/insulin-like growth factor I (IGF-I) system by the treatment with a sustained release formulation of a recombinant bovine GH (rBGH), is a good strategy to investigate growth optimization in aquaculture fish species. To further deepen into the knowledge of rBGH effects in fish and to estimate the growth potential of juveniles of gilthead sea bream, the present work evaluated rBGH injection on growth, GH/IGF-I axis and lipid metabolism modulation, and explored the conservation of GH effects provoked by the in vivo treatment using in vitro models of different tissues. The rBGH treatment increased body weight and specific growth rate (SGR) in juveniles and potentiated hyperplastic muscle growth while reducing circulating triglyceride levels. Moreover, the results demonstrated that the in vivo treatment enhanced also lipolysis in both isolated hepatocytes and adipocytes, as well as in day 4 cultured myocytes. Furthermore, these cultured myocytes extracted from rBGH-injected fish presented higher gene expression of GH/IGF-I axis-related molecules and myogenic regulatory factors, as well as stimulated myogenesis (i.e. increased protein expression of a proliferation and a differentiation marker) compared to Control fish-derived cells. These data, suggested that cells in vitro can retain some of the pathways activated by in vivo treatments in fish, what can be considered an interesting line of applied research. Overall, the results showed that rBGH stimulates somatic growth, including specifically muscle hyperplasia, as well as lipolytic activity in gilthead sea bream juveniles.

Acting locally - affecting globally: RNA sequencing of gilthead sea bream with a mild Sparicotyle chrysophrii infection reveals effects on apoptosis, immune and hypoxia related genes

BACKGROUND

Monogenean flatworms are the main fish ectoparasites inflicting serious economic losses in aquaculture. The polyopisthocotylean Sparicotyle chrysophrii parasitizes the gills of gilthead sea bream (GSB, Sparus aurata) causing anaemia, lamellae fusion and sloughing of epithelial cells, with the consequent hypoxia, emaciation, lethargy and mortality. Currently no preventive or curative measures against this disease exist and therefore information on the host-parasite interaction is crucial to find mitigation solutions for sparicotylosis. The knowledge about gene regulation in monogenean-host models mostly comes from freshwater monopysthocotyleans and almost nothing is known about polyopisthocotyleans. The current study aims to decipher the host response at local (gills) and systemic (spleen, liver) levels in farmed GSB with a mild natural S. chrysophrii infection by transcriptomic analysis.

RESULTS

Using Illumina RNA sequencing and transcriptomic analysis, a total of 2581 differentially expressed transcripts were identified in infected fish when compared to uninfected controls. Gill tissues in contact with the parasite (P gills) displayed regulation of fewer genes (700) than gill portions not in contact with the parasite (NP gills) (1235), most likely due to a local silencing effect of the parasite. The systemic reaction in the spleen was much higher than that at the parasite attachment site (local) (1240), and higher than in liver (334). NP gills displayed a strong enrichment of genes mainly related to immune response and apoptosis. Processes such as apoptosis, inflammation and cell proliferation dominated gills, whereas inhibition of apoptosis, autophagy, platelet activation, signalling and aggregation, and inflammasome were observed in spleen. Proteasome markers were increased in all tissues, whereas hypoxia-related genes were down-regulated in gills and spleen.

CONCLUSIONS

Contrasting forces seem to be acting at local and systemic levels. The splenic down-regulation could be part of a hypometabolic response, to counteract the hypoxia induced by the parasite damage to the gills and to concentrate the energy on defence and repair responses. Alternatively, it can be also interpreted as the often observed action of helminths to modify host immunity in its own interest. These results provide the first toolkit for future studies towards understanding and management of this parasitosis.

Determination of Seasonal Vitamin and Mineral Contents of Sea Bream (Sparus aurata L., 1758) Cultured in Net Cages in Central Black Sea Region

This study aimed to determine the seasonal vitamin and mineral contents of sea bream (Sparus aurata) cultured in net cages in Central Black Sea region. The average seasonal A, D₃, and E vitamins values in fish meat were between 0.27 ± 0.02-0.60 ± 0.00, 0.98 ± 0.01-1.70 ± 0.00, and 3.10 ± 0.14-6.00 ± 0.21 mg/kg, respectively (p < 0.05). The average seasonal Ca, Fe, K, Mg, Na, P, Zn, and Se values in fish meat were between 276.90 ± 0.99-1788.50 ± 51.27 (p < 0.05), 3.50 ± 0.12-4.47 ± 0.18 (p > 0.05), 4244.50 ± 8.84-4761.50 ± 1.06 (p < 0.05), 251.55 ± 2.55-312.65 ± 11.42 (p < 0.05), 56.49 ± 0.04-128.75 ± 0.18 (p < 0.05), 2234.50 ± 15.20-2619.00 ± 7.07 (p < 0.05), 5.62 ± 0.10-15.30 ± 0.22 (p < 0.05), and 0.30 ± 0.00-0.38 ± 0.01 mg/kg (p > 0.05), respectively. As a result, it can be concluded that sea bream cultured in the Central Black Sea region is a rich source of nutrients in terms of vitamins and mineral matters, and fish size, feed quality, and the environmental factors are influential on the contents of vitamin and mineral substances in the fish tissue.

What can we learn from glucocorticoid administration in fish? Effects of cortisol and dexamethasone on intermediary metabolism of gilthead seabream (Sparus aurata L.)

In aquaculture facilities fish welfare could be compromised due to stressors. Fish deal with stress, inter alia, through the activation of the hypothalamic-pituitary-interrenal endocrine axis and, as a result, corticosteroids are released into the blood. Recent studies have described that corticosteroids actions depend on the specific affinities to their receptors, and the subsequent differentiated responses. Cortisol is the main corticosteroid hormone in teleost fish, being its actions dependent on the intensity and time of exposure to stressors. Short-term effects of corticosteroids are well described, but long-term effects, including changes in the energy management directly affecting growth and survival, are less understood in fish. Here we show the effects of chronic oral administration of cortisol and the synthetic glucocorticoid dexamethasone (DXM) on the intermediary metabolism of the gilthead seabream (Sparus aurata). We described a higher energy expenditure associated to both corticosteroids resulting in lower growth rates of fish. Moreover, the effects of these compounds were tissue-dependant, with differences between both hormones. Thus, cortisol-fed animals accumulated triglycerides in the liver, while DXM treatment led to glycogen storage. Cortisol and DXM stimulated amino acids catabolism and gluconeogenic pathways in muscle and gills, but the effects were significantly enhanced in DXM-fed fish. The described effects highlighted differentiated mechanisms of action associated to both corticosteroids under chronic stress conditions. Further studies should aim at describing those pathways in detail, with special attention to the functionality of glucocorticoid receptor isoforms. The effects described here for S. aurata juveniles, may serve as a basis to assess long-term stress in future comparative studies with other aquaculture species.

Lymphocystis disease virus (LCDV-Sa), polyomavirus 1 (SaPyV1) and papillomavirus 1 (SaPV1) in samples of Mediterranean gilthead seabream

Lymphocystis disease, caused by the iridovirus lymphocystis disease virus (LCDV), is characterized by the appearance of tumour-like lesions on the skin of affected animals associated with several environmental factors and/or with stress due to the intensive culture conditions of fish farms. In a previous study, the genomes of a new LCDV species, LCDV-Sa, were detected, together with 2 previously unknown viruses, Sparus aurata papillomavirus 1 (SaPV1) and Sparus aurata polyomavirus 1 (SaPyV1). Gilthead seabream from 17 fish farms in Spain, Italy and Turkey were sampled between 2009 and 2015 to investigate the role of the newly described SaPV1 and SaPyV1 viruses in lymphocystis disease development. Our results show that in diseased fish, either or both of the new viruses are almost invariably detected together with LCDV (98%). In asymptomatic fish, these viruses were detected in a much lower percentage (28%) and mostly in concurrence with LCDV (24%). These data confirm the suspected association among the 3 different viruses during lymphocystis disease development in gilthead seabream and warrant future studies to establish their respective contributions.

Contribution of Non-canonical Cortisol Actions in the Early Modulation of Glucose Metabolism of Gilthead Sea Bream (Sparus aurata)

Teleost fish are exposed to diverse stressors in farming and wildlife conditions during their lifespan. Cortisol is the main glucocorticoid hormone involved in the regulation of their metabolic acclimation under physiological stressful conditions. In this context, increased plasma cortisol is associated with energy substrate mobilization from metabolic tissues, such as liver and skeletal muscle, to rapidly obtain energy and cope with stress. The metabolic actions of cortisol have primarily been attributed to its genomic/classic action mechanism involving the interaction with intracellular receptors, and regulation of stress-responsive genes. However, cortisol can also interact with membrane components to activate rapid signaling pathways. In this work, using the teleost fish gilthead sea bream (Sparus aurata) as a model, we evaluated the effects of membrane-initiated cortisol actions on the early modulation of glucose metabolism. For this purpose, S. aurata juveniles were intraperitoneally administrated with cortisol and with its membrane impermeable analog, cortisol-BSA. After 1 and 6 h of each treatment, plasma cortisol levels were measured, together with glucose, glycogen and lactate in plasma, liver and skeletal muscle. Transcript levels of corticosteroids receptors (gr1, gr2, and mr) and key gluconeogenesis (g6pc and pepck)- and glycolysis (pgam1 and aldo) related genes in the liver were also measured. Cortisol and cortisol-BSA administration increased plasma cortisol levels in S. aurata 1 h after administration. Plasma glucose levels enhanced 6 h after each treatment. Hepatic glycogen content decreased in the liver at 1 h of both cortisol and cortisol-BSA administration, while increased at 6 h due to cortisol but not in response to cortisol-BSA. Expression of gr1, g6pc, pgam1, and aldo were preferentially increased by cortisol-BSA in the liver. Taking all these results in consideration, we suggest that non-canonical cortisol mechanisms contribute to the regulation of the early glucose metabolism responses to stress in S. aurata.

Come rain or come shine: environmental effects on the infective stages of Sparicotyle chrysophrii, a key pathogen in Mediterranean aquaculture

BACKGROUND

Evidence concerning the environmental influence on monogenean transmission and infection processes is widely accepted, although only the effects of a limited number of abiotic factors on particular monogenean species have been explored. The current context of climate change calls for further research both on this subject, and also that concerning monogenean hosts, especially in aquaculture.

METHODS

In this study, four experiments were used to assess the response of the infective stages of Sparicotyle chrysophrii, a pathogenic monogenean from gilthead sea bream (Sparus aurata) cultures in the Mediterranean, to variations of temperature (from 10 °C to 30 °C), pH (7.0 and 7.9), photoperiod (LD 12:12, LD 0:24 and LD 24:0) and salinity (from 27 ppt to 47 ppt).

RESULTS

Thermal variations cause the strongest responses among the infective stages of S. chrysophrii, which reduced development and survival times as temperature increased. The optimal thermal range for maximum hatching success was found between 14 and 22 °C, whereas temperatures of 10 and 30 °C probably represent biological thermal limits. Reductions of development time and hatching rates were recorded at the lowest pH level, but hatching success remained above 50%, suggesting a certain degree of tolerance to slight pH variations. Photoperiod acts as an environmental cue synchronising the circadian hatching rhythm of S. chrysophrii with the first four hours of darkness. Response to a wide range of salinities was negligible, suggesting a high tolerance to variations of this abiotic factor.

CONCLUSIONS

Larval development and hatching of S. chrysophrii are modulated according to environmental factors, mainly temperature, thus parasite-host coordination and successful infections are enhanced. Therefore, abiotic factors should be broadly considered to design treatments against this monogenean. The high tolerance to the predicted environmental variations over the next century reported for gilthead sea bream and herein exposed for S. chrysophrii suggests that neither will be notably affected by climate change in the western Mediterranean region.

Characterization and Expression Dynamics of Key Genes Involved in the Gilthead Sea Bream (Sparus aurata) Cortisol Stress Response during Early Ontogeny

The present study identified and characterized six key genes involved in the hypothalamic-pituitary-interrenal (HPI) axis of gilthead sea bream (Sparus aurata), a commercially important European aquaculture species. The key genes involved in the HPI axis for which gene structure and synteny analysis was carried out, comprised of two functional forms of glucocorticoid receptors (GR), as well as three forms of pro-opiomelanocortin (POMC) genes and one form of mineralocorticoid receptor (MR) gene. To explore their functional roles during development but also in the stress response, the expression profiles of gr1, gr2, mr, pomc_aI, pomc_aII, and pomc_β were examined during early ontogeny and after an acute stress challenge. The acute stress challenge was applied at the stage of full formation of all fins, where whole body cortisol was also measured. Both the cortisol and the molecular data implied that sea bream larvae at the stage of the full formation of all fins at 45 dph are capable of a response to stress of a similar profile as observed in adult fish.

Administration of chitosan-tripolyphosphate-DNA nanoparticles to knockdown glutamate dehydrogenase expression impairs transdeamination and gluconeogenesis in the liver

Glutamate dehydrogenase (GDH) plays a major role in amino acid catabolism. To increase the current knowledge of GDH function, we analysed the effect of GDH silencing on liver intermediary metabolism from gilthead sea bream (Sparus aurata). Sequencing of GDH cDNA from S. aurata revealed high homology with its vertebrate orthologues and allowed us to design short hairpin RNAs (shRNAs) to knockdown GDH expression. Following validation of shRNA-dependent downregulation of S. aurata GDH in vitro, chitosan-tripolyphosphate (TPP) nanoparticles complexed with a plasmid encoding a selected shRNA (pCpG-sh2GDH) were produced to address the effect of GDH silencing on S. aurata liver metabolism. Seventy-two hours following intraperitoneal administration of chitosan-TPP-pCpG-sh2GDH, GDH mRNA levels and immunodetectable protein decreased in the liver, leading to reduced GDH activity in both oxidative and reductive reactions to about 53-55 % of control values. GDH silencing decreased glutamate, glutamine and aspartate aminotransferase activity, while increased 2-oxoglutarate content, 2-oxoglutarate dehydrogenase activity and 6-phosphofructo-1-kinase/fructose-1,6-bisphosphatase activity ratio. Our findings show for the first time that GDH silencing reduces transdeamination and gluconeogenesis in the liver, hindering the use of amino acids as gluconeogenic substrates and enabling protein sparing and metabolisation of dietary carbohydrates, which would reduce environmental impact and production costs of aquaculture.

Modulation of immune genes mRNA levels in mucosal tissues and DNA damage in red blood cells of Sparus aurata by gold nanoparticles

Gold nanoparticles (AuNP) effects on Sparus aurata were evaluated on skin, gills and intestine by assessing the expression of immune genes and in peripheral blood evaluating genetic damage. Fish were exposed to 0.5 and 50 μg/L AuNP for 96 h. Results showed that exposure to 50 μg/L AuNP induced an upregulation in the expression of innate immune genes in gills (c3, lys, il1β, tnfα, il6, il10 and tgfβ) and intestine (il1β, tnfα and il6). Furthermore, mRNA levels of hsp70 and hsp90 were increased in gills after exposure to 0.5 μg/L AuNP, when compared to 50 μg/L. Present data demonstrated the sensitivity of gills and intestines to AuNP exposure supporting their use in the study of fish responses to other nanoparticles. Genotoxic potential of AuNP was demonstrated by increased DNA strand breaks in red blood cells of fish exposed to AuNP, suggesting that AuNP represent a potential hazard to fish.

Enhancement of broodstock health and maternal immunity in gilthead seabream (Sparus aurata L.) using ExcelMOS®

The current study was conducted to investigate the effect of ExcelMOS® in enhancing the immune system of Sparus aurata broodstock and their impact on offspring health through displaying the maternal transfer of immunity. Broodstock were divided into two groups: one was injected intraperitoneally with ExcelMOS® 1 month before spawning, while the other group was used as a control (without injection). Comprehensive increase in survival rate was observed for larvae hatched from ExcelMOS®-injected broodstock than those of the control (P ≤ 0.05). Hematological analysis showed increases in leukocyte count and hematocrit percentage (P ≤ 0.05) and significant enhancement in immune assays as phagocytic, respiratory burst, lysozyme activities in ExcelMOS®-injected broodstock (P ≤ 0.05). Additionally, total immunoglobulin levels in the serum, eggs, and larvae resulted from ExcelMOS®-injected broodstock were highly significant (P ≤ 0.05) than those in the control ones. Transmission electron microscopy and semi-thin sections in posterior intestine of ExcelMOS®-injected broodstock revealed reinforcement of the epithelial barrier structure, intestinal integrity, and functionality in combination with the stimulation of innate immune system. In conclusion, immunostimulation of Sparus aurata broodstock using ExcelMOS® has improved survival of larvae and enhanced both innate and adaptive immune defense mechanisms. Further investigations are required to show the effect of ExcelMOS® on fish cultured in intensive culture systems.

Gene expression of thyrotropin- and corticotrophin-releasing hormones is regulated by environmental salinity in the euryhaline teleost Sparus aurata

In euryhaline teleosts, the hypothalamus-pituitary-thyroid and hypothalamus-pituitary-interrenal axes (HPT and HPI, respectively) are regulated in response to environmental stimuli such as salinity changes. However, the molecular players participating in this physiological process in the gilthead seabream (Sparus aurata), a species of high value for aquaculture, are still not identified and/or fully characterized in terms of gene expression regulation. In this sense, this study identifies and isolates the thyrotropin-releasing hormone (trh) mRNA sequence from S. aurata, encoding prepro-Trh, the putative factor initiating the HPT cascade. In addition, the regulation of trh expression and of key brain genes in the HPI axis, i.e., corticotrophin-releasing hormone (crh) and corticotrophin-releasing hormone-binding protein (crhbp), was studied when the osmoregulatory status of S. aurata was challenged by exposure to different salinities. The deduced amino acid structure of trh showed 65-81% identity with its teleostean orthologs. Analysis of the tissue distribution of gene expression showed that trh mRNA is, though ubiquitously expressed, mainly found in brain. Subsequently, regulation of gene expression of trh, crh, and crhbp was characterized in fish acclimated to 5-, 15-, 40-, and 55-ppt salinities. In this regard, the brain gene expression pattern of trh mRNA was similar to that found for the crh gene, showing an upregulation of gene expression in seabream acclimated to the highest salinity tested. Conversely, crhbp did not change in any of the groups tested. Our results suggest that Trh and Crh play an important role in the acclimation of S. aurata to hypersaline environments.

Impact of Air Exposure on Vasotocinergic and Isotocinergic Systems in Gilthead Sea Bream (Sparus aurata): New Insights on Fish Stress Response

The hypothalamus-pituitary-interrenal (HPI) and hypothalamus-sympathetic-chromaffin cell (HSC) axes are involved in the regulation of the stress response in teleost. In this regard, the activation of a complex network of endocrine players is needed, including corticotrophin-releasing hormone (Crh), Crh binding protein (Crhbp), proopiomelanocortin (Pomc), thyrotropin-releasing hormone (Trh), arginine vasotocin (Avt), and isotocin (It) to finally produce pleiotropic functions. We aimed to investigate, using the gilthead sea bream (Sparus aurata) as a biological model, the transcriptomic response of different endocrine factors (crh, crhbp, pomcs, trh), neuropeptides (avt and it), and their specific receptors (avtrv1a, avtrv2, and itr) in four important target tissues (hypothalamus, pituitary, kidney and liver), after an acute stress situation. We also investigated several stress hormones (catecholamines and cortisol). The stress condition was induced by air exposure for 3 min, and hormonal, metabolic and transcriptomic parameters were analyzed in a time course response (15 and 30 min, and 1, 2, 4, and 8 h post-stress) in a total of 64 fish (n = 8 fish per experimental group; p = 0.05; statistical power = 95%). Our results showed that plasma noradrenaline, adrenaline and cortisol values increased few minutes after stress exposure. At hypothalamic and hypophyseal levels, acute stress affected mRNA expression of all measured precursors and hormonal factors, as well as their receptors (avtrs and itr), showing the activation, at central level, of HPI, HSC, and Avt/It axes in the acute stress response. In addition, stress response also affected mRNA levels of avtrs and itr in the head kidney, as well as the steroidogenic acute regulatory protein (star) and tyrosine hydroxylase (th) expression, suggesting their participation in the HPI and HSC axes activation. Moreover, the pattern of changes in hepatic avtrs and itr gene expression also highlights an important role of vasotocinergic and isotocinergic pathways in liver metabolic organization after acute stress events. Our results demonstrate, both at transcriptional and circulating levels of several hormones, the existence of a complex activation of different endocrine pathways in S. aurata related to the stress pathways, where vasotocinergic and isotocinergic systems can also be considered key players of the acute stress response orchestration.

Osmoregulatory role of vasotocinergic and isotocinergic systems in the gilthead sea bream (Sparus aurata L)

Gilthead sea bream, Sparus aurata L., is an important fish species for the Mediterranean aquaculture and is considered a good model for studying the osmoregulatory process, due to its capacity to cope with great changes in environmental salinity (5-60‰). Our group studied the osmoregulatory role of different endocrine systems in this species, focusing on the vasotocinergic and isotocinergic systems over several years. For this purpose, the cDNAs coding for pro-vasotocin (pro-vt), pro-isotocin (pro-it), two arginine vasotocin (AVT) receptors (avtr v1a2- and v2-types) and one IT receptor (itr) were cloned. Acclimation to different environmental salinities induced a direct lineal relationship between plasma AVT levels and salinity, with no changes in plasma IT values. In addition, higher values in vasotocinergic, isotocinergic and stress pathways (pro-vt and pro-it gene expression, AVT and IT storage and plasma cortisol levels) in both hypo- and/or hyper-osmotic transfers, suggest an interaction between cortisol and AVT/IT pathways. Moreover, gene expression of specific receptors, as well as the use of different in vitro techniques, demonstrated an important osmoregulatory orchestration in different organs. In addition, individuals intraperitoneally injected with AVT and transferred to different environmental salinities enhanced plasma cortisol levels and/or gill Na⁺, K⁺-ATPase activity. These effects could be related to the energy repartitioning process occurring during osmotic adaptation of S. aurata to extreme environmental salinities, which could be mediated not only by plasma cortisol but also by AVT. Finally, our results indicated a very important role of the vasotocinergic and/or isotocinergic systems in both osmoregulatory and non-osmoregulatory organs.

Preliminary studies on haematological and plasmatic parameters in gilthead sea bream (Sparus aurata) held under day/night temperature variations

This study aimed to evaluate to what extent diel water temperature oscillations over a short period of time (41 h) affected haematologic and plasmatic parameters of gilthead sea bream. Sea bream juveniles (160 fish; 177.2 ± 20.9 g) were divided in two homogenous groups, experimental and control. The experimental group was exposed to water at 22.3 ± 0.6 °C between 5 a.m. and 5 p.m. and to colder water from 5 p.m. to 5 a.m. (temperature variation of 8.6 ± 0.3 °C) during 41h period, whereas for the control group, water temperature was maintained constant (22.4 ± 0.7 °C) for the same period. Fish were fed three times per day (10:30 a.m., 2 p.m., 4 p.m.). Blood was collected from fish caudal veins (n = 6) at different time points (10 a.m., 1 p.m., 5 p.m., 6:30 p.m., 8 p.m. and 10 a.m. of the following day) from each group, for haematologic (haematocrit and haemoglobin) and plasmatic (glucose, cortisol, triglycerides and total protein) determinations. All parameters studied tended to vary throughout the study period, both for experimental and control groups. Significant differences were observed between the two groups for all the studied parameters at different sampling points. These differences were observed near the influence of the cold-water period or during the cooling-water period. Results suggested that colder water temperature cycles depressed fish metabolic activity and affected the levels of the analysed blood-circulating metabolites. Overall, results suggested that stress response was similar for experimental and control groups and that gilthead sea bream were able to cope with diel water temperature variations.

Recombinant bovine growth hormone (rBGH) enhances somatic growth by regulating the GH-IGF axis in fingerlings of gilthead sea bream (Sparus aurata)

The growth hormone (GH)/insulin-like growth factors (IGFs) endocrine axis is the main growth-regulator system in vertebrates. Some authors have demonstrated the positive effects on growth of a sustained-release formulation of a recombinant bovine GH (rBGH) in different fish species. The aim of this work was to characterize the effects of a single injection of rBGH in fingerlings of gilthead sea bream on growth, GH-IGF axis, and both myogenic and osteogenic processes. Thus, body weight and specific growth rate were significantly increased in rBGH-treated fish respect to control fish at 6weeks post-injection, whereas the hepatosomatic index was decreased and the condition factor and mesenteric fat index were unchanged, altogether indicating enhanced somatic growth. Moreover, rBGH injection increased the plasma IGF-I levels in parallel with a rise of hepatic mRNA from total IGF-I, IGF-Ic and IGF-II, the binding proteins IGFBP-1a and IGFBP-2b, and also the receptors IGF-IRb, GHR-I and GHR-II. In skeletal muscle, the expression of IGF-Ib and GHR-I was significantly increased but that of IGF-IRb was reduced; the mRNA levels of myogenic regulatory factors, proliferation and differentiation markers (PCNA and MHC, respectively), or that of different molecules of the signaling pathway (TOR/AKT) were unaltered. Besides, the growth inhibitor myostatin (MSTN1 and MSTN2) and the hypertrophic marker (MLC2B) expression resulted significantly enhanced, suggesting altogether that the muscle is in a non-proliferative stage of development. Contrarily in bone, although the expression of most molecules of the GH/IGF axis was decreased, the mRNA levels of several osteogenic genes were increased. The histology analysis showed a GH induced lipolytic effect with a clear decrease in the subcutaneous fat layer. Overall, these results reveal that a better growth potential can be achieved on this species and supports the possibility to improve growth and quality through the optimization of its culture conditions.

Development of sea bream (Sparus aurata) semen vitrification protocols

The long-term goal of this research project is to set up efficient protocol that can be used to develop a standardized approach for vitrification of marine fish spermatozoa. In particular, the aim of the present study was to develop a vitrification protocol for sea bream (Sparus aurata) spermatozoa. To draw up the protocol, we tested two different dilution media (1% NaCl and Mounib medium), three different vitrification devices (loops, drops and cut straws), different cryoprotectants (CPs) and three different equilibration times (30, 60 and 120 s). The effect of the different vitrification procedures on spermatozoa quality was checked by measuring spermatozoa motility rate and viability, mitochondrial membrane potential and the fertilizing ability of both fresh and post-thawed gametes. The best result was obtained by dropping directly into liquid nitrogen 20 μl of spermatozoa suspension (drop-wise method) diluted with Mounib buffer containing 10% Me₂SO + 10% glycerol. The addition of a mixture of anti-freezing proteins, AFPI and AFPIII, to Mounib buffer significantly increases the spermatozoa quality following vitrification so confirming the usefulness of AFPs in improving the quality of gametes subjected to the vitrification process. The present study proves that vitrification offers an alternative to conventional sperm cryopreservation also in this species.