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Stress triggers a battery of physiological responses in fish, including the activation of metabolic pathways involved in energy production, which helps the animal to cope with the adverse situation. Prolonged exposure to stressful farming conditions may induce adverse effects at the whole-animal level, impairing welfare. Fourier transform infrared (FTIR) spectroscopy is a rapid biochemical fingerprinting technique, that, combined with chemometrics, was applied to disclose the metabolic alterations in the fish liver as a result of exposure to standard stressful practices in aquaculture. Gilthead seabream (Sparus aurata) adults exposed to different stressors were used as model species. Spectra were preprocessed before multivariate statistical analysis. Principal components analysis (PCA) was used for pattern recognition and identification of the most discriminatory wavenumbers. Key spectral features were selected and used for classification using the k-nearest neighbour (KNN) algorithm to evaluate whether the spectral changes allowed for the reliable discrimination between experimental groups. PCA loadings suggested that major variations in the hepatic infrared spectra responsible for the discrimination between the experimental groups were due to differences in the intensity of absorption bands associated with proteins, lipids and carbohydrates. This broad-range technique can thus be useful in an exploratory approach before any targeted analysis.

Hepatic metabolic adjustments are key adaptive mechanisms to stress in fish targeting at increasing energy availability for the animal to efficiently cope with a stressor. Teleosts exhibit a broad variety of these metabolic responses, depending on the species biology, individual experiences and the challenge’s characteristics. Nevertheless, the molecular response to a prolonged stress can be more heterogeneous and far more complex to interpret than that to an acute stress. A comparative proteomics analysis was employed to discover the set of liver proteins involved in the adaptive processes that tune the physiological response of Sparus aurata to different suboptimal rearing conditions and physical challenges. Three separated trials were established where fish were submitted to different conditions (overcrowding, net handling and hypoxia). The response at the transcript level of 13 genes was also assessed. Mass spectrometric analysis revealed 71 differential abundant proteins distributed among the trials. Prolonged exposure to stress seems to have induced widespread changes in amino acid, carbohydrate, and lipid metabolisms, antioxidant response and protein folding, sorting and degradation processes. Two genes corresponding to heat-shock proteins were found to be differently expressed in net handled fish. These results shed light on the dynamics and extent of this species’ metabolic reprogramming under different challenges, supporting future studies on stress markers’ discovery and fish welfare research.

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One of the main constraints in aquaculture production is farmed fish vulnerability to diseases due to husbandry practices or external factors like pollution, climate changes, or even the alterations in the dynamic of product transactions in this industry. It is though important to better understand and characterize the intervenients in the process of a disease outbreak as these lead to huge economical losses in aquaculture industries. High-throughput technologies like proteomics can be an important characterization tool especially in pathogen identification and the virulence mechanisms related to host-pathogen interactions on disease research and diagnostics that will help to control, prevent, and treat diseases in farmed fish. Proteomics important role is also maximized by its holistic approach to understanding pathogenesis processes and fish responses to external factors like stress or temperature making it one of the most promising tools for fish pathology research.

Consumption of aquatic food, including fish, accounts for 17% of animal protein intake. However, fish consumption might also result in several side-effects such as sneezing, swelling and anaphylaxis in sensitized consumers. Fish allergy is an immune reaction to allergenic proteins in the fish muscle, for instance parvalbumin (PV), considered the major fish allergen. In this study, we characterize PV in two economically important fish species for southern European aquaculture, namely gilthead seabream and European seabass, to understand its stability during in vitro digestion and fish processing. This information is crucial for future studies on the allergenicity of processed fish products. PVs were extracted from fish muscles, identified by mass spectrometry (MS), and detected by sandwich enzyme-linked immunosorbent assay (ELISA) after simulated digestion and various food processing treatments. Secondary structures were determined by circular dichroism (CD) after purification by anion exchange and gel filtration chromatography. In both species, PVs presented as α-helical and β-sheet structures, at room temperature, were shown to unfold at boiling temperatures. In European seabass, PV detectability decreased during the simulated digestion and after 240 min (intestinal phase) no detection was observed, while steaming showed a decrease (p < 0.05) in PVs detectability in comparison to raw muscle samples, for both species. Additionally, freezing (−20 °C) for up to 12 months continued to reduce the detectability of PV in tested processing techniques. We concluded that PVs from both species are susceptible to digestion and processing techniques such as steaming and freezing. Our study obtained preliminary results for further research on the allergenic potential of PV after digestion and processing.

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