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Evaluating the survival of discarded species is gaining momentum after the new European Common Fisheries Policy (Article 15 of the European Regulation No. 1380/2013). This regulation introduced a discard ban, with an exemption for those species with demonstrated high survival rates after their capture and release. Candidate species should be evaluated for each fishing gear and geographical area. In this study, we assessed not only survival, but also physiological recovery rates of blackspot seabream (Pagellus bogaraveo) below commercial size captured with a hookline called “voracera” in the Strait of Gibraltar (SW Atlantic waters of Europe). Experiments onboard a commercial fishing vessel were paralleled with studies in controlled ground-based facilities, where the capture process was mimicked, and physiological recovery markers were described. Our results confirmed that hookline capture induced acute stress responses in the target species, such as changes in plasma cortisol, lactate, glucose, and osmolality. However, 90.6% of the blackspot seabreams below commercial size captured with this fishing gear managed to survive, and evidenced physiological recovery responses 5 h after capture, with complete homeostatic recovery occurring within the first 24 h. Based on this study, the European Commission approved an exemption from the discard (EU Commission Delegated Regulation 6794/2018). Thus, the robust methodology described herein can be an important tool to mitigate the problem of discards in Europe.

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.

The use of lysed microalgae in the diet of carnivorous fish can increase the bioavailability of proteins and bioactive compounds, such as unsaturated fatty acids or vitamins in the digestive tract. These are essential molecules for the proper physiological development of fish in aquaculture. However, some antinutritional components and other undesirable molecules can be released from an excess of microalgae supplied, compromising the integrity of the intestine. The inclusion of small amounts of hydrolized microalgae in the fish diet can be a good strategy to avoid negative effects, improving the availability of beneficial compounds. Nannochloropsis gaditana is an interesting microalgae as it contains nutraceuticals. Previous studies reported beneficial effects after its inclusion in the diet of Sparus aurata, a widely cultured species in Europe and in all Mediterranean countries. However, administration of raw microalgae can produce intestinal inflammation, increased intestinal permeability, bacterial translocation and disturbance of digestion and absorption processes. The aim of this study was to evaluate changes in the intestinal microbiota and barrier stability of S. aurata fed with low inclusion (5%) hydrolysed N. gaditana. Intestinal microbiota was analyzed using Illumina MiSeq technology and libraries were constructed using variable regions V3–V4 of 16S rDNA molecules. Analysis were based in the identification, quantification and comparison of sequences. The predictive intestinal microbial functionality was analyzed with PICRUSt software. The results determined that the intestinal microbiota bacterial composition and the predictive intestinal microbiota functionality did not change statistically after the inclusion of N. gaditana on the diet. The study of gene expression showed that genes involved in intestinal permeability and integrity were not altered in fish treated with the experimental diet. The potential functionality and bacterial taxonomic composition of the intestinal microbiota, and the expression of integrity and permeability genes in the intestine of the carnivorous fish S. aurata were not affected by the inclusion of hydrolysed 5% N. gaditana microalgae.

Sea bream (Sparus aurata Linneaus) was acclimated to three salinity concentrations, viz. 5 (LSW), 38 (SW) and 55psμ (HSW) and three water temperatures regimes (12, 19 and 26 °C) for five weeks. Osmoregulatory capacity parameters (plasma osmolality, sodium, chloride, cortisol, and branchial and renal Na+,K+-ATPase activities) were also assessed. Salinity and temperature affected all of the parameters tested. Our results indicate that environmental temperature modulates capacity in sea bream, independent of environmental salinity, and set points of plasma osmolality and ion concentrations depend on both ambient salinity and temperature. Acclimation to extreme salinity resulted in stress, indicated by elevated basal plasma cortisol levels. Response to salinity was affected by ambient temperature. A comparison between branchial and renal Na+,K+-ATPase activities appears instrumental in explaining salinity and temperature responses. Sea bream regulate branchial enzyme copy numbers (Vmax) in hyperosmotic media (SW and HSW) to deal with ambient temperature effects on activity; combinations of high temperatures and salinity may exceed the adaptive capacity of sea bream. Salinity compromises the branchial enzyme capacity (compared to basal activity at a set salinity) when temperature is elevated and the scope for temperature adaptation becomes smaller at increasing salinity. Renal Na+,K+-ATPase capacity appears fixed and activity appears to be determined by temperature., This study was partly supported by grants AGL2007-61211/ACU (Ministerio de Innovación y Ciencia and FEDER, Spain) and Proyecto de Excelencia PO7-RNM-02843 (Junta de Andalucía) to JMM. L.V.C. is funded FONDAP-IDEAL 15150003.

In 2019, Europe will adopt a no-discards policy in fisheries. This entails the landing of captured species unless strong evidence is provided supporting their survival and recovery after fishing. Thus, research on this topic is gaining momentum. Bottom-trawling, as a non-selective fishing method, is characterized by a high proportion of discards including vulnerable key species, such as demersal sharks. Their survival may also depend on capture depth. By paralleling onboard and laboratory experiments with the small-spotted catshark, Scyliorhinus canicula, we offer a robust experimental design to assess the survival of discarded sharks. Catsharks were captured by bottom-trawling at two depths (shallow similar to 89 m and deep similar to 479 m). Blood samples were collected following trawl capture and analyzed for stress biomarkers (lactate, osmolality, phosphate, urea). During recovery in onboard tanks, behavior was video-recorded and fish were re-sampled after 24 h. A second experiment was conducted in laboratory facilities to simulate air-exposure after trawling and to analyze the physiological recovery. Our results showed that 95.7% of the animals survived 24 h after trawling. We confirmed that trawling elicited acute stress responses in catshark but that they managed to recover. This was demonstrated by lactate concentrations that were 2.6 mM upon capture, but recovered to assumed baselines after 24 h (0.2 mM). Non-invasive video monitoring revealed behavioral differences with depth, whereby those captured at 89 m depth required longer to recover than those captured at 479 m depth. Implementation of standardized survival studies by fishery managers can benefit from holistic physiological approaches, such as the one proposed here. European UnionEuropean Union (EU) PADI Foundation [28467] Ministerio de Economia y CompetitividadSpanish Government [AGL2013-48835-C2-R, AGL2016-76069-C2-1-R] Project SUREDEPAR (Programa Pleamar, Ministerio de Agricultura y Pesca, Alimentacion y Medio Ambiente) Ministry of Science and Higher EducationMinistry of Science and Higher Education, Poland European Social Funds through the Portuguese National Science Foundation (FCT)Portuguese Foundation for Science and Technology [PTDC/MAR-BIO/3034/2014] FCTPortuguese Foundation for Science and Technology [UID/Multi/04326/2013]

the intestine of marine fishes contributes to the ocean carbon cycle producing carbonate aggregates as part of the osmoregulatory process. Therefore, this study aimed to evaluate physiological adjustments of European sea bass (Dicentrarchus labrax) intestine to a higher pCO(2) environment likely in the near future (similar to 1700 mu atm). At the whole-body level, hypercapnia for 5 weeks resulted in fish having a significantly diminished specific growth rate, condition factor and hepatosomatic index. An increase in plasma osmolality and HCO3- concentration was detected, paralleled by decreased metabolites concentrations. In the intestine, high seawater pCO(2) was without effect on ouabain-sensitive ATPase activities, while Bafilomycin A1-sensitive ATPase activity significantly decreased in the anterior intestine. Anterior and mid intestine were mounted in Ussing chambers in order to measure bioelectrical parameters and bicarbonate secretion by pH-Stat ex-vivo. Hypercapnia induced a 2.3 and 2.8-fold increase in bicarbonate secretion rates in the anterior and mid intestine, respectively. In the intestinal fluid, HCO3- concentration increased 2.2-fold, and carbonate precipitates showed a 4.4-fold increase in response to hypercapnia, paralleled by a > 3-fold increase of drinking and a > 2-fold increase of intestinal volume at any given time. At the molecular level, hypercapnia elicited higher intestinal mRNA expression levels for atp6v1b (V-ATPase B subunit), slc4a4, slc26a3, and slc26a6, both in the anterior and mid intestine. As a whole, our results show that the intestine of sea bass responds to high seawater pCO(2), a response that comes at a cost at the whole-body level with an impact in the fish specific growth rate, condition factor, and hepatosomatic index. Ministry of Science and Higher Education, Portugal European Social Funds through the Portuguese National Science Foundation (FCT)[PTDC/MAR-BIO/3034/2014] Portuguese Foundation for Science and Technology (FCT) [UID/Multi/04326/2019] info:eu-repo/semantics/publishedVersion

Fish welfare is gaining momentum due to consumers' trends and legal regulations. Therefore, aquaculture industry is in the way of mitigating stress to the animals and, thus, improving the physiological status, with the consequent increase in economical profits. As a consequence, feed additives have been proposed as potential stress relievers through the diet. However, the effectiveness of these extracts on stress responses and growth regulation is still to be defined for different species and stressors. Here we show the effects of the commercial natural-additive “Relaquax” on growth performance, endocrine regulation of hypothalamic-pituitary-interrenal (HPI) and somatotropic (GH/IGF-I) axes, as well as intermediary metabolism, of gilthead seabream (Sparus aurata L.) reared in low and high stocking density conditions. For this purpose, S. aurata juveniles were maintained for 3 months at different combined conditions of feeding (control diet or supplemented with the additive) and initial stocking density (low or high; 4.0 or 11.5 kg m−3, respectively). At the end of the experimental period, brain, pituitary, head kidney and liver gene expression of endocrine factors involved in stress and growth regulation were determined. In addition, liver and muscle enzyme activities of the intermediary metabolism of carbohydrates, lipids and amino acids were assessed. Our results showed an increased growth performance in fish fed with the additive, mediated through hepatic igf1 enhanced expression at both stocking densities. In the same way, higher body mass was associated to inhibition of lipid catabolism in muscle (decreased GPDH and HADH activities), as a consequence of diet supplementation. The additive has also reduced amino acid catabolism in liver (decreased AST activity), as well as enhanced glycolysis in muscle (increased PK activity). In conclusion, this additive was confirmed as a natural alternative to improve aquaculture and welfare of seabream, especially under high stocking density conditions., This work was funded by Spanish Ministry of Science and Innovation - MICINN (AGL2013-48835-C2-1-R and AGL2016-76069-C2-1-R) awarded to JMM. IJC was supported by a contract from the University of Cádiz (PIF UCA/REC02VIT/2014; 2018-011/PU/AY.PUENTE/CD). The authors (IJC, IR-J, and JMM) belong to the Fish Welfare and Stress Network (AGL2016-81808-REDT), supported by the Agencia Estatal de Investigación (MICINN, Spanish Government).

The European Fisheries Policy aims at a progressive elimination of discards. An exception from this regulation includes the release of species with high survival rates after capture. In south-western Atlantic waters of Europe, Norway lobster (Nephrops norvegicus) and spottail mantis shrimp (Squilla mantis) are amongst the most important crustacean species captured by bottom trawling. We evaluated their short-term survival probability, survival rates and recovery capacities after being trawled by an oceanographic vessel. Seasonal differences were considered by sampling in spring and autumn. In order to characterise the full recovery after capture, physiological responses were also analysed along a time-course of 24 h. Our results confirm that bottom trawling is a stressful process to these crustacean species, as seen by changes in plasma and muscle metabolites, hemocyanin and immune system parameters. However, maintaining captured animals in onboard water tanks evidenced the full physiological recovery of survivors after 6 h and before 24 h. Survival in Norway lobster and spottail mantis shrimp varied according to the season, being higher in spring (68.4 � 7.1% and 87.0 � 4.7%, respectively) than in autumn (33.8 � 7.8% and 63.8 � 9.3%, respectively), probably due to the higher temperatures registered after summer months. The employment of the presented techniques for the evaluation of other crustaceans, fishing gears and geographical areas can be contemplated. Fisheries stakeholders might use this approach to better manage discards in Europe, Sí

Land use carries implications for freshwater fish conservation. Plantation forestry practices have been shown to have negative impacts on resident fish fauna, but little work has been conducted to assess these impacts on invasive vs. native fish populations. Ten headwater catchments in the Mediterranean climate zone of Chile were used to assess the impacts of land use (pine plantations vs. native forests) on fish condition (length-weight relationship) and abundance (catch-per-unit-effort (CPUE)) of the invasive trout Oncorhynchus mykiss and the threatened native catfish Nematogenys inermis. Negative impacts on trout condition were associated with a lack of canopy cover and river topology. The presence of N. inermis was associated with catchment factors less favourable to trout. Current environmental regulations and forestry management practices do not appear to create negative pressures on invasive trout from land use practices, despite expectations from the literature. Assessing how land use management regulations impact invasive and native fishes should be a part of species conservation and territorial planning.

In this study we assessed the influence of three different environmental salinities (5, 15 and 31 psu during 90 days) on growth, osmoregulation, energy metabolism and digestive capacity in juveniles of the Notothenioid fish Eleginops maclovinus. At the end of experimental time samples of plasma, liver, gill, intestine, kidney, skeletal muscle, stomach and pyloric caeca were obtained. Growth, weight gain, hepatosomatic index and specific growth rate increased at 15 and 31 psu and were lower at 5 psu salinity. Gill Na(+), K(+)-ATPase (NKA) activity presented a "U-shaped" relationship respect to salinity, with its minimum rates at 15 psu, while this activity correlated negatively with salinity at both anterior and posterior intestinal portions. No significant changes in NKA activity were observed in kidney or mid intestine. Large changes in plasma, metabolite levels and enzymatic activities related to energy metabolism in liver, gill, intestine, kidney and muscle were generally found in the groups exposed to 5 and 31 psu compared to the 15 psu group. Only the pepsin activity (digestive enzymes) assessed enhanced with environmental salinity, while pyloric caeca trypsin/chymotrypsin ratio decreased. This study suggests that juvenile of E. maclovinus presents greater growth near its iso-osmotic point (15 psu) and hyperosmotic environment (31 psu). Acclimation to low salinity increased the osmoregulatory expenditure as seen by the gill and anterior intestine results, while at high salinity, branchial osmoregulatory activity was also enhanced. This requires the mobilization of lipid stores and amino acids, thereby holding the growth of fish back. The subsequent reallocation of energy sources was not sufficient to maintain the growth rate of fish exposed to 5 psu. Thus, E. maclovinus juveniles present better growth efficiencies in salinities above the iso-osmotic point and hyperosmotic environment of this species, showing their best performance at 15 psu as seen by the main osmoregulatory and energy metabolism enzymatic activities.

The influence of stocking density and food deprivation on energy metabolism, stress processes and the pituitary endocrine system of silver catfish (Rhamdia quelen) was investigated after a period of 14 days, in which plasmatic and hepatic parameters and the mRNA expression of prolactin (PRL), growth hormone (GH) and somatolactin (SL) were assessed. The fish were subjected to four experimental conditions: (1) fed under high stocking density (32 kg/m3, HSD); (2) fed under mean stocking density (16 kg/m3, MSD); (3) fed under low stocking density (8 kg/m3, LSD); and (4) food-deprived under low stocking density (8 kg/m3, LSD-FD). After 14 days, plasma and liver samples were obtained to analyze the metabolite levels and enzymatic activities related to metabolism, and pituitary glands were obtained to analyze hormone expression (PRL, GH and SL). Liver weight and the hepato-somatic index (HSI) revealed that specimens maintained at HSD and/or MSD had higher hepatic stores, which were observed in the triglyceride and glycogen levels in this tissue, than animals submitted to the LSD and LSD-FD groups. Triglyceride levels in the plasma and liver revealed the consumption of fatty acid reserves in the fasting group. Enzymatic activities, such as glutamate dehydrogenase (GDH), phosphorylase (GPase), pyruvate kinase (PK), aspartate transaminase (AST) and glycerol-3-phosphate dehydrogenase (G3PDH), indicated an increase in gluconeogenic pathways in the HSD group and an increase in glycolitic metabolism in the LSD groups. The expression of PRL was not affected by stocking density and/or food deprivation and GH decreased with increased density and increased in fasting conditions. A negative effect of density and fasting was observed on the expression of SL. Overall, the data suggested that juvenile silver catfish reared at stocking densities of 16 to 32 kg/m3 were better maintained than those maintained at the lowest density., We would like to thank the financial support by CAPES (Ministry of Education of Brazil, Brazil) through the program PDSE-CAPES (Programa Institutional de Bolsas de Doutorado Sanduíche no Exterior — Process: 1585/12-6) to C.M., the CNPq research fellowships to V.L.L. and B.B., the project AGL2010-14876 (Ministry of Science and Education, Spain) to J.M.M. and the program FPU (Formación de Profesorado Universitario — Ref. AP2008-01194) (Ministry of Science and Education, Spain) to JAM-S.

Osmoregulation in fish is a complex process that requires the orchestrated cooperation of many tissues. In fish facing hyperosmotic environments, the intestinal absorption of some monovalent ions and the secretion of bicarbonate are key processes to favor water absorption. In the present study, we showed that bicarbonate levels in the intestinal fluid are several fold higher in seawater than in freshwater acclimated tilapia (Oreochromis mossambicus). In addition, we analyzed gene expression of the main molecular mechanisms involved in HCO3- movements i.e. slc26a6, slc26a3, slc4a4 and v-type H-ATPase sub C in the intestine of tilapia acclimated to both seawater and freshwater. Our results show an anterior/posterior functional regionalization of the intestine in tilapia in terms of expression patterns, which is affected by environmental salinity mostly in the anterior and mid intestine. Analysis of bicarbonate secretion using pH-Stat in tissues mounted in Ussing chambers reveals high rates of bicarbonate secretion in tilapia acclimated to seawater from anterior intestine to rectum ranging between similar to 900 and similar to 1700 nmol HCO3- cm(-2) h(-1). However, a relationship between the expression of slc26a6, slc26a3, slc4a4 and the rate of bicarbonate secretion seems to be compromised in the rectum. In this region, the low expression of the bicarbonate transporters could not explain the high bicarbonate secretion rates here described. However, we postulate that the elevated v-type H-ATPase mRNA expression in the rectum could be involved in this process. (C) 2017 Elsevier Inc. All rights reserved. University of Cadiz, Spain FCT, Portugal [SFRH/BD/113363/2015] Portuguese Foundation for Science and Technology (Ministry of Science and Higher Education, Portugal) [PTDC/MAR-BIO/3034/2014] Portuguese Foundation for Science and Technology (European Social Funds) [PTDC/MAR-BIO/3034/2014] national funds from the Portuguese Foundation for Science and Technology (FCT) [UID/Multi/04326/2013]

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., This study was funded by project AGL2010-14876 from Ministerio de Ciencia e Innovación awarded to J. M. M. (Spain). This work was partially supported by Ph.D. scholarship from the University of Cadiz (UCA 2009-074-FPI) awarded to I. R-J.

The aim of this study was to evaluate immunological, metabolic and osmoregulatory secondary stress responses in Eleginops maclovinus specimens submitted to three different stocking densities: i) low (3.1 kg m(-3)), medium (15 kg m(-3)) and high (60 kg m(-3)) during 10 days, alone or in combination with a previous treatment of a protein extract of the pathogen Piscirickettsia salmonis (0.5 μg g weight body(-1)). Plasma, liver, gill and kidney samples were obtained at the end of both experiments. Plasma cortisol and amino acid levels increased, while plasma glucose, triglyceride and lactate levels decreased at higher stocking densities. However, no effects were observed on serum Immunoglobulin type M (IgM anti P. salmonis level) values. Gill Na(+), K(+)-ATPase activity enhanced under these experimental conditions, suggesting an osmotic imbalance. Energy metabolism changes, assessed by metabolite concentrations and enzyme activities, indicated a reallocation of energetic substrates at higher stocking densities. Specimens inoculated with a protein extract of P. salmonis and maintained at different stocking densities showed primary stress response, as all groups enhanced plasma cortisol concentrations. Serum IgM levels increased after treatment with P. salmonis extract but a negative influence of high stocking density on IgM production was observed when immune system was activated. Furthermore, treatment with P. salmonis protein extract evoked deep changes in the metabolite stores in all tissues tested, indicating a mobilization of energy substrates in response to infection. The results show that stocking density induced immunological, metabolic and osmoregulatory secondary stress responses in E. maclovinus specimens and that previous treatment with P. salmonis compromise these changes.

The aim of this study was to carry out a comparative analysis of the osmoregulatory properties and associated energy metabolism of euryhaline flatfish species that are cultured in the world. Culture of flatfish (pleuronectiformes) requires stage- and species-dependent osmotic conditions for rearing. Additionally, geographic origin of broodstock animals is another factor to be taken into account for the culture of pleuronectiformes. Larval and juvenile stages of many flatfish species are cultured in large nurseries situated in estuaries and shallow marine habitats, where the environmental salinity is close to the iso-osmotic point of their internal milieu. This fact implicates an advantage in terms of energy savings for osmoregulatory purposes. Thus, this ‘saved’ energy can be derived to other physiological processes, such as somatic growth. However, this scientific presumption does not always results in an optimal growth for many flatfish species. Indeed, iso-osmotic culture conditions can evoke a higher allostatic load than that in the usual hyper-osmotic environment where flatfish species live wildly. Optimization of flatfish culture thus requires adjustments of the osmotic culture conditions to the specific osmoregulatory and metabolic demands that eventually determine the allostatic load and consequently condition growth rates. In this sense, the geographical location of aquaculture farms and the osmoregulatory-based selection of the species to be cultivated in a particular area become critical factors to be considered for optimal flatfish culture.

Marine fish contribute to the carbon cycle by producing mineralized intestinal aggregates generated as by-products of their osmoregulation. Here we aimed at characterizing the control of intestinal aggregate production in the gilthead sea bream in response to near future increases of environmental CO2. Our results demonstrate that hypercapnia (800 and 1200 μatm CO2) elicits higher intestine epithelial HCO3−secretion and the subsequent parallel increase of intestinal aggregate production when compared to present values (400 μatm CO2). Intestinal gene expression analysis revealed the up-regulation of crucial transport mechanisms involved not only in the intestinal secretion cascade (Slc4a4, Slc26a3 and Slc26a6) of sea bream, but also in other mechanisms involved in intestinal ion uptake linked to water absorption such asNKCC2and theAquaporin 1b.These results highlight the important role of fish in the marine carbon cycle, and their potential growing impact of intestinal biomineralization processes in the scenario of ocean acidification.

Fish are continuously forced to actively absorb or expel water and ions through epithelia. Most studies have focused on the gill due to its role in Na+ and Cl- trafficking. However, comparatively few studies have focused on the changing function of the intestine in response to external salinity. Therefore, the present study investigated the main intestinal changes of long-term acclimation of the Senegalese sole (Solea senegalensis) to 5,15, 38 and 55 ppt. Through the measurement of short-circuit current (Isc) in Ussing chambers and biochemical approaches, we described a clear anterior/posterior functional regionalization of the intestine in response to salinity. The use of specific inhibitors in Ussing chamber experiments, revealed that the bumetanide-sensitive Na+/K+/Cl- co-transporters are the main effectors of Cl- uptake in both anterior intestine and rectum. Additionally, the use of the anion exchanger specific inhibitor, DIDS, showed a salinity/region dependency of anion exchanger function. Moreover, we also described ouabain-sensitive Na+/K+-ATPase (NKA) and Bafilomycin Al-sensitive H-ATPase activities (HA), which displayed changes related to salinity and intestinal region. However, the most striking result of the present study is the description of an omeprazole-sensitive H+/K+-ATPase (HKA) in the rectum of Senegalese sole. Its activity was consistently measurable and increased at lower salinities, reaching rates even higher than those of the NKA. Together our results provide new insights into the changing role of the intestine in response to external salinity in teleost fish. The rectal activity of HKA offers an alternative/cooperative mechanism with the HA in the final processing of intestinal water absorption by apical titration of secreted bicarbonate. (C) 2016 Elsevier Inc. All rights reserved. Ministry of Science and Education, Spain [AGL2010-14876] Ministry of Science and Higher Education European Social Funds through the Portuguese National Science Foundation (FCT) [PTDC/MAR-BIO/3811/2012, PTDC/MAR-BIO/3034/2014] Portuguese Foundation for Science and Technology (FCT) [UID/Multi/04326/2013]

Eleginops maclovinus is an endemic, subantarctic Notothenioidei species. This study examined the influence of different environmental salinities (5, 15, and 45 psu; and 32 psu as a control) on energy metabolism in E. maclovinus over a period of 14 days. Metabolite contents and enzymatic activities related to carbohydrate, amino acid, and lipid metabolisms were evaluated in metabolic (liver) and osmoregulatory (gill and kidney) tissues. At extreme salinities (5 and 45 psu), the liver showed a high consumption of energy reserves, mainly as amino acids and carbohydrates. Carbohydrate metabolism in the gills did not change under different salinities, but increased lactate levels were found, suggesting that this tissue may use lactate as an energy substrate. Amino acid metabolism in the gills decreased at 5 psu but increased at 45 psu, and lipid metabolism increased at 5 and 15 psu during the first days of the trial, indicating a possible use of lipids as energy. Kidney carbohydrate catabolism and amino acid metabolism increased after 14 days at 45 psu, while lipid metabolism did not vary in relation to salinity changes. Together, these results suggest that the liver is most affected by salinity changes, probably due to its role as a supplier of energetic substrates. The gills and kidney, osmoregulatory tissues, maintained their energy metabolism levels with minor modifications. In conclusion, E. maclovinus exhibits metabolic adjustments to adapt to different salinities, showing the best responses in isosmotic environmental salinities.

Thyroid hormones are involved in many developmental and physiological processes, including osmoregulation. The regulation of the thyroid system by environmental salinity in the euryhaline gilthead seabream (Sparus aurata) is still poorly characterized. To this end seabreams were exposed to four different environmental salinities (5, 15, 40 and 55 ppt) for 14 days, and plasma free thyroid hormones (fT3, fT4), outer ring deiodination and Na+/K+-ATPase activities in gills and kidney, as well as other osmoregulatory and metabolic parameters were measured. Low salinity conditions (5 ppt) elicited a significant increase in fT3 (29%) and fT4 (184%) plasma concentrations compared to control animals (acclimated to 40 ppt, natural salinity conditions in the Bay of Cádiz, Spain), while the amount of pituitary thyroid stimulating hormone subunit β (tshb) transcript abundance remained unchanged. In addition, plasma fT4 levels were positively correlated to renal and branchial deiodinase type 2 (dio2) mRNA expression. Gill and kidney T4-outer ring deiodination activities correlated positively with dio2 mRNA expression and the highest values were observed in fish acclimated to low salinities (5 and 15 ppt). The high salinity (55 ppt) exposure caused a significant increase in tshb expression (65%), but deiodinase gene expression (dio1 and dio2) and activity did not change and were similar to controls (40 ppt). In conclusion, acclimation to different salinities led to changes in the peripheral regulation of thyroid hormone metabolism in seabream. Therefore, thyroid hormones are involved in the regulation of ion transport and osmoregulatory physiology in this species. The conclusions derived from this study may also allow aquaculturists to modulate thyroid metabolism in seabream by adjusting culture salinity., This work was partially supported by a Socrates/Erasmus Grant from the European Union and a Ph.D. scholarship from the University of Cadiz (UCA 2009-074-FPI) to I. R-J. It has been also supported by grants AGL2007-61211/ACU (Ministerio de Educación y Ciencia and FEDER, Spain) and Proyecto de Excelencia PO7-RNM-02843 (Junta de Andalucía) to J.M.M. BL (SFRH/BPD/89889/2012) and PISP (SFRH/BPD/84033/2012) were supported by the Science Foundation (FCT) of Portugal.

Item does not contain fulltext Senegalese sole (Solea senegalensis) is a eurytherm teleost that under natural conditions can be exposed to annual water temperature fluctuations between 12 and 26 degrees C. This study assessed the effects of temperature on sole metabolic status, in particular in what concerns plasma free amino acid changes during thermal acclimation. Senegalese sole maintained at 18 degrees C were acclimated to either cold (12 degrees C) or warm (26 degrees C) environmental temperatures for 21 days. Fish maintained at 18 degrees C served as control. Plasma concentrations of cortisol, glucose, lactate, triglycerides, proteins, and free amino acids were assessed. Cold acclimation influenced interrenal responses of sole by increasing cortisol release. Moreover, plasma glucose and lactate concentrations increased linearly with temperature, presumably reflecting a higher metabolic activity of sole acclimated to 26 degrees C. Acclimation temperature affected more drastically plasma concentrations of dispensable than that of indispensable amino acids, and different acclimation temperatures induced different responses. Asparagine, glutamine and ornithine seem to be of particular importance for ammonia detoxification mechanisms, synthesis of triglycerides that may be used during homeoviscous adaptation and, to a lesser extent, as energetic substrates in specimens acclimated to 12 degrees C. When sole is acclimated to 26 degrees C taurine, glutamate, GABA and glycine increased, which may suggest important roles as antioxidant defences, in osmoregulatory processes and/or for energetic purposes at this thermal regimen. In conclusion, acclimation to different environmental temperatures induces several metabolic changes in Senegalese sole, suggesting that amino acids may be important for thermal acclimation. 01 juli 2012

The effects of prolonged feed deprivation were assessed on blood plasma metabolites and free amino acid levels in Solea senegalensis. Juvenile specimens were maintained at two experimental conditions (24 h fasted and 21 days feed-deprived). In feed-deprived fish, relative growth rate and hepatosomatic index as well as plasma triglycerides and proteins levels were significantly lower. However, plasma cortisol levels were higher in feed-deprived fish, while plasma glucose and lactate values were not significantly different between treatments. Furthermore, feed-deprived fish showed higher levels of total plasma free amino acids than 24 h fasted fish. In 21 days feed-deprived sole, an increase in plasma cortisol levels may suggest a functional role in mobilizing energy due to the catabolic action of this hormone in teleosts. Higher levels of glutamine, arginine and ornithine in 21 days feed-deprived fish may be indicative of a dual role for these amino acids: ammonia detoxification and carbon source for gluconeogenesis. The increased plasma glucogenic and branched-chain amino acid levels, together with the maintenance of plasma glucose in 21 days feed-deprived sole, suggest active liver gluconeogenic processes supported by tissue proteolysis.

We have investigated the regulation of thyroidal status and osmoregulatory capacities in juveniles from the teleost Solea senegalensis acclimated to different ambient temperatures. Juveniles, raised in seawater at 19°C, were acclimated for 3 weeks to temperatures of 12, 19 and 26°C. Since our preliminary observations showed that at 12°C feed intake was suppressed, our experimental design controlled for this factor. The concentration of branchial Na+,K+-ATPase, estimated by measurements of enzyme activity at the optimum temperature of this enzyme (37°C), did not change. In contrast, an increase in Na+,K+-ATPase activity (measured at 37°C), was observed in the kidney of 12°C-acclimated fish. In fish acclimated to 12°C, the hepatosomatic index had increased, which correlated with increased plasma levels of triglycerides and non-esterified fatty acids. Plasma cortisol levels did not differ significantly between the experimental groups. In liver and gills, the amount of iodothyronine deiodinases that exhibit thyroid hormone outer ring deiodination was up-regulated only when fish did not feed. When assayed at the acclimation temperature, kidney deiodinase activities were similar, indicating a temperature-compensation strategy. 3,5,3′-triiodothyronine (T3) tissue concentrations in gills and kidney did not differ significantly between experimental groups. However, at 12°C, lower T3 tissue levels were measured in plasma and liver. We conclude that S. senegalensis adjusts its osmoregulatory system to compensate for the effects of temperature on electrolyte transport capacity. The organ-specific changes in thyroid hormone metabolism at different temperatures indicate the involvement of thyroid hormones in temperature acclimation.

The influence of culture density on growth, stress system and metabolism has been assessed in A. regius juveniles submitted to different initial stocking densities (3, 7, 10 and 13 g L− 1) for 40 days. On days 0, 12, 27 and 40 of the experiment, biometric parameters were measured. In addition, plasma, liver and muscle samples were taken for biochemical analysis at the end of experimental time. Our results showed better growth rates and feed utilization in those specimens held at high stocking densities when compared to those under low stocking densities. In addition, higher plasma cortisol, glucose and triglycerides levels found in the lowest stocking density tested suggest an activation of the stress system in fish held at this condition. Moreover, no changes in hepatic metabolites were observed, while values of muscle triglycerides, amino acids and lactate enhanced when stocking density increased. In conclusion, the culture of juvenile A. regius at higher initial densities (at least 13 g L− 1) ensures better growth and the optimization of the existing facilities, improving welfare of this species in aquaculture systems., Study funded by project AGL2013-48835-C2-1-R (Ministerio de Economía y Competitividad, Spain) awarded to J.M.M.

Background Marine species have colonized extreme environments during evolution such as freshwater habitats. The amphidromous teleost fish, Galaxias maculatus is found mainly migrating between estuaries and rivers, but some landlocked populations have been described in lakes formed during the last deglaciation process in the Andes. In the present study we use mtDNA sequences to reconstruct the historical scenario of colonization of such a lake and evaluated the osmoregulatory shift associated to changes in habitat and life cycle between amphidromous and landlocked populations. Results Standard diversity indices including the average number of nucleotide differences (Π) and the haplotype diversity index (H) indicated that both populations were, as expected, genetically distinctive, being the landlocked population less diverse than the diadromous one. Similarly, pairwise GST and NST comparison detected statistically significant differences between both populations, while genealogy of haplotypes evidenced a recent founder effect from the diadromous stock, followed by an expansion process in the lake. To test for physiological differences, individuals of both populations were challenged with a range of salinities from 0 to 30 ppt for 8 days following a period of progressive acclimation. The results showed that the landlocked population had a surprisingly wider tolerance to salinity, as landlocked fish survival was 100% from 0 to 20 ppt, whereas diadromous fish survival was 100% only from 10 to 15 ppt. The activity of ATPase enzymes, including Na+/K+-ATPase (NKA), and H+-ATPase (HA) was measured in gills and intestine. Activity differences were detected between the populations at the lowest salinities, including differences in ATPases other than NKA and HA. Population differences in mortality are not reflected in enzyme activity differences, suggesting divergence in other processes. Conclusions These results clearly demonstrate the striking adaptive changes of G. maculatus osmoregulatory system, especially at hyposmotic environments, associated to a drastic shift in habitat and life cycle at a scale of a few thousand years.

The effects of starvation and re-feeding on metabolites and tissue composition, GH/IGF-I axis, and digestive enzyme activities in juvenile thick-lipped grey mullet (Chelon labrosus) were evaluated. Fish were divided into three feeding groups (n = 72, 82.00 ± 4.09 g initial body mass). The control group was fed 1% of their body mass once a day throughout the experiment with commercial pellets. The other two groups were deprived of feed for 21 days (starved), or re-fed for 7 days after 14 days of food deprivation (re-fed). Full-length cDNAs from pituitary GH and hepatic IGF-I were cloned by screening a cDNA library or by PCR techniques. Furthermore, changes in their mRNA expressions were assessed by real time PCR in specimens maintained under the different feeding patterns. Results showed a negative growth in starved and re-feeding groups. Starvation induced a significant increase in plasma triglycerides as well as a decrease in liver glucose and glycogen. Re-feeding increased plasma glucose, lactate and protein, as well as liver glucose and glycogen. In addition, starvation significantly increased pituitary GH expression, while re-feeding down-regulated it. No significant changes were observed in hepatic IGF-I expression in any dietary treatment. Digestive enzyme activities were not significantly affected either by starvation or by re-feeding. The results of the present work suggest that juveniles of the thick-lipped grey mullet may easily adjust their metabolism under situations characterized by a short-term starvation and re-feeding., This work was funded by project AGL2010-14876 from MICINN to JMM.

The aim of this study was to determine the impact of diets with different plant protein ingredients on proximate composition, tissue metabolites and tissue fatty acid composition, as well as hepatic and intestinal histological modifications in Senegalese sole (Solea senegalensis). Fish (21.5 ± 2.8 g body weight) were fed six isonitrogenous and isoenergetic diets during 11 weeks. A control diet containing fish meal as the main protein source was compared with five experimental diets replacing 30% fish meal protein by different plant protein sources: soybean meal (SBM), soybean protein concentrate (SPC), soybean protein isolate (SPI), wheat gluten meal (WGM) or pea protein concentrate (PPC). The inclusion of different plant protein did not significantly affect growth and proximate composition of fish. The hepatosomatic index was not significantly different to the control group; however, utilization of WGM significantly increased hepatocyte size. Plasma protein values and muscle triglycerides were influenced by the inclusion of SBM and WGM in the diets respectively. Feeding fish on SBM, WGM and PPC diets significantly enhanced n-6 fatty acid levels in muscle, particularly linoleic acid. None of the plant protein ingredient used in the diets decreased arachidonic, eicosapentaenoic as well as docosahexaenoic acid values in liver and muscle. Overall, histological studies did not reveal the existence of any intestinal alterations induced by the inclusion of different plant proteins. Despite moderate changes produced by SBM, SPC and WGM, inclusion of dietary plant protein ingredients has no major impact on growth, tissue and blood biochemistry, fatty acid profile and gut integrity of Senegalese sole juveniles.

This study investigated the effects of prolonged exposure of silver catfish (Rhamdia quelen) to the essential oil (EO) of Hesperozygis ringens. Ventilatory rate (VR), stress and metabolic indicators, energy enzyme activities, and mRNA expression of adenohypophyseal hormones were examined in specimens that were exposed for 6 h to 0 (control), 30 or 50 µL L−1 EO of H. ringens in water. Reduction in VR was observed in response to each treatment, but no differences were found between treatments. Plasma glucose, protein, and osmolality increased in fish exposed to 50 µL L−1. Moreover, lactate levels increased after exposure to both EO concentrations. Plasma cortisol levels were not changed by EO exposure. Fish exposed to 30 µL L−1 EO exhibited higher glycerol-3-phosphate dehydrogenase (G3PDH) activity, while exposure to 50 µL L−1 EO elicited an increase in glucose-6-phosphate dehydrogenase (G6PDH), fructose-biphosphatase (FBP), and 3-hydroxyacyl-CoA-dehydrogenase (HOAD) activities compared with the control group. Expression of growth hormone (GH) only decreased in fish exposed to 50 µL L−1 EO, while somatolactin (SL) expression decreased in fish exposed to both concentrations of EO. Exposure to EO did not change prolactin expression. The results indicate that GH and SL are associated with energy reorganization in silver catfish. Fish were only slightly affected by 30 µL L−1 EO of H. ringens, suggesting that it could be used in practices where a reduction in the movement of fish for prolonged periods is beneficial, i.e., such as during fish transportation., This study was supported by research funds from the Fundação de Amparo à Pesquisa do Estado do Rio Grande do Sul (FAPERGS/PRONEX), Ministério da Pesca/Ministério da Ciência e Tecnologia/FINEP, Conselho Nacional de Pesquisa e Desenvolvimento Científico (CNPq) and by project AGL2013-48835-C2-1-R (Ministerio de Economía y Competividad) to J.M. Mancera (Spain). B. Baldisserotto received a research fellowship from CNPq. C. Toni and C.G. Pinheiro received PhD fellowships from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), and J.A. Martos-Sitcha is supported by a PhD fellowship (FPU, Reference AP2008-01194) from Ministerio de Educación (Spain).

11 pages, 5 figures, 1 table, It now is widely recognised that the global temperature is rising, a phenomenon which could alter the effects of pollution on wildlife. In order to assess the role of temperature and exposure to chlorine due to cooling water discharges, a battery of metabolic, oxidative stress and histological parameters were evaluated in Mytilus galloprovincialis after 15 and 30 days at 15 °C and at two increased temperatures (+5 and + 10 °C). Diverse gill pathologies such as haemolymphatic sinus dilatation, an increased number of mucocytes and granulocytes as well as a lower number of cilia were observed after 30 days exposure at higher temperatures. Protein, amino acid, triglyceride and fatty acid levels decreased when the temperature increased, as a consequence of higher energetic demand. Similarly, acetylcholinesterase, catalase and glutathione S-transferase activities showed an inhibition at higher temperatures, although gill lipid peroxidation levels remained unaffected. Our results suggest that increased temperatures induce deterioration in the health status of themussels and in their defensive capacity against a polluted environment, This research work was funded by grant CTM2009-09527 and CSD2007-0055 to E.N.