BackgroundWater temperature greatly influences the physiology and behaviour of teleost fish as other aquatic organisms. While fish are able to cope with seasonal temperature variations, thermal excursions outside their normal thermal range might exceed their ability to respond leading to severe diseases and death.Profound differences exist in thermal tolerance across fish species living in the same geographical areas, promoting for investigating the molecular mechanisms involved in susceptibility and resistance to low and high temperatures toward a better understanding of adaptation to environmental challenges. The gilthead sea bream, Sparus aurata, is particularly sensitive to cold and the prolonged exposure to low temperatures may lead to the "winter disease", a metabolic disorder that significantly affects the aquaculture productions along the Northern Mediterranean coasts during winter-spring season. While sea bream susceptibility to low temperatures has been extensively investigated, the cascade of molecular events under such stressful condition is not fully elucidated.ResultsIn the present study two groups of wild sea bream were exposed for 21 days to two temperature regimes: 16 ± 0.3°C (control group) and 6.8 ± 0.3°C (cold-exposed group) and DNA microarray analysis of liver transcriptome was carried out at different time points during cold exposure.A large set of genes was found to be differentially expressed upon cold-exposure with increasingly relevant effects being observed after three weeks at low temperature. All major known responses to cold (i.e. anti-oxidant response, increased mitochondrial function, membrane compositional changes) were found to be conserved in the gilthead sea bream, while, evidence for a key role of unfolded protein response (UPR) to endoplasmic reticulum (ER) stress, during short- and long-term exposure to cold is reported here for the first time.ConclusionsTranscriptome data suggest a scenario where oxidative stress, altered lipid metabolism, ATP depletion and protein denaturation converge to induce ER stress. The resulting UPR activation further promotes conditions for cell damage, and the inability to resolve ER stress leads to severe liver dysfunction and potentially to death.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-765) contains supplementary material, which is available to authorized users.

The EU Marine Strategy Framework Directive 2008/56/EC (MSFD) defines a framework for Community actions in the field of marine environmental policy in order to achieve and/or maintain the Good Environmental Status (GES) of the European seas by 2020. Microbial assemblages (from viruses to microbial-sized metazoa) provide a major contribution to global biodiversity and play a crucial role in the functioning of marine ecosystems, but are largely ignored by the MSFD. Prokaryotes are only seen as "microbial pathogens," without defining their role in GES indicators. However, structural or functional prokaryotic variables (abundance, biodiversity and metabolism) can be easily incorporated into several MSFD descriptors (i.e. D1. biodiversity, D4. food webs, D5. eutrophication, D8. contaminants and D9. contaminants in seafood) with beneficial effects. This review provides a critical analysis of the current MSFD descriptors and illustrates the reliability and advantages of the potential incorporation of some prokaryotic variables within the set of indicators of marine environmental quality. Following a cost/benefit analysis against scientific and economic criteria, we conclude that marine microbial components, and particularly prokaryotes, are highly effective for detecting the effects of anthropogenic pressures on marine environments and for assessing changes in the environmental health status. Thus, we recommend the inclusion of these components in future implementations of the MSFD.

Summary Blood chemistry profiles of cultured sturgeon hybrids Acipenser naccarii female × Acipenser baerii male were assessed in order to acquire basic data for evaluating fish health status on‐farm. Sixty healthy fish (11.0 ± 3.2 Kg weight; 117.8 ± 8.6 cm total length) were randomly captured from 600 m3 concrete tanks and sampled from April to June. Blood samples were analyzed for the following 22 biochemical parameters using standard clinical methods: cortisol, glucose, lactate, non esterified fatty acids, triglycerides, cholesterol, albumin, creatinine, urea, total bilirubin, total protein, aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, creatine phosphokinase, lactate dehydrogenase, calcium, phosphorus, magnesium, sodium, potassium and chloride. Biochemical values were found to be consistent with data from the parental species A. naccarii. Cortisol, cholesterol, albumin, urea, total bilirubin, CK, LDH and magnesium were significantly affected by sampling time and the differences are probably related to sexual maturation of the fish. Blood chemistry analyses afforded an accurate evaluation of sturgeons’ health status, also providing information on their reproductive conditions. Evidence resulting from cortisol and lactate values indicated that pre‐sampling operations, including capture and confinement of these large‐sized fish, must be carefully managed in order to minimize handling stress. This study provides knowledge on blood chemistry of hybrid sturgeon A. naccarii × A. baerii and the results corroborate the validity of the test panel performed in evaluating the physiological functions of sturgeons. Reference values for 22 biochemical parameters were identified for the purpose of evaluating health and welfare in cultured sturgeons.

A 9-week feeding trial was performed to evaluate the effects of fishmeal (FM) replacement by a mixture of plant proteins (PP), consisted of wheat gluten, soybean meal and soy protein concentrate, on the growth performance and welfare of turbot juveniles (initial weight 9.7 AE 0.2 g). Four isonitrogenous and isolipidic diets contained FM at 500 g kg À1 (FM50), 350 g kg À1 (FM35), 200 g kg À1 (FM20) and 50 g kg À1 (FM5). A decreased feed intake and an increased feed conversion rate was observed in FM5 group. Specific growth rate was significantly reduced in FM20 and FM5 groups, whereas protein and lipid utilization and proximate whole body composition were significantly different in FM5 group. Serum cortisol significantly increased in FM20 and FM5 groups whereas cholesterol, triglycerides, NEFA, total protein and urea concentrations significantly decreased. Serum lysozyme and blood phagocytes increased in FM20 and FM5 groups. FM35 ensured growth close to FM50, without significant effects on health and welfare of animals. FM20 and FM5 groups displayed reduced growth, metabolic stress and an immune response with effects on health and welfare. Results highlighted the consistency between growth performance and welfare status, suggesting the usefulness of their combined assessment for evaluating the suitability of PP and to improve dietary formulation for turbot.

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