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Territoriality, spatial exploration and social hierarchy are strictly related behaviors in gregarious fishes, and are often under-appreciated in farms where the individuals are confined within crowded spaces. In this study, we investigated the role of spatial exploration, elucidating the importance of time upon forming the social organization, and the role of the territoriality in gilthead seabream (Sparus aurata), using two experimental approaches. In the first approach, three fish were placed sequentially in the aquarium with an interval of two days (sequential model), while in the second (simultaneous model), two fish were simultaneously placed in an aquarium divided by a barrier which was removed after a certain period of time. To study the effect of social stress and spatial perception in the two models, we monitored behavior (aggressive acts and feeding priority), integrated with the evaluation of physiological and cellular stress parameters, such as phagocytosis, cortisol, glucose, and blood osmolarity levels. After the establishment of the social hierarchy in the "sequential model", we observed that the levels of cortisol and an immunological cell-mediated marker were higher in subordinate individuals than in the dominant ones. We observed a different modulation of phagocytic activity in peritoneal cavity cells between dominant and subordinates, demonstrating that social stress acts upon immune response. Differently from the first model, no behavioral, physiological, or phagocytic differences were found between the two fish involved in the simultaneous model, where both fish acted as co-dominants, defending their territory. The study achieved a deeper understanding of the role of spatial exploration, territorial dominance and intraspecific interaction in gilthead seabream, and elucidated the link between them and physiological stress indicators. The results highlight aspects of interest to the aquaculture industry, showing the importance of a greater focus on rearing conditions, finding solutions to mitigate crowding effects and promoting the quality of aquacultural products. [ABSTRACT FROM AUTHOR]

The expansion of aquaculture practices in coastal areas can alter the balance of microbial communities in nearby marine ecosystems with negative impacts on both farmed and natural species, as well as on human health through their consumption. Among marine filter-feeder invertebrates, poriferans are known as effective microbial bioremediators, even though they are currently still underutilized in association with fish mariculture plants. In this study, we investigate the microbial bioremediation capability of the demosponge Hymeniacidon perlevis in an experimental land-based fish farm where this species occurred consistently in the drainage conduit of the wastewater. Microbiological analyses of cultivable vibrios, total culturable bacteria (37 °C), fecal and total coliforms, and fecal enterococci were carried out on the fish farm wastewater in two sampling periods: autumn and spring. The results showed that H. perlevis is able to filter and remove all the considered bacterial groups from the wastewater, including human potential pathogens, in both sampling periods. This finding sustains the hypothesis of H. perlevis use as a bioremediator in land-based aquaculture plants as well. [ABSTRACT FROM AUTHOR]

Social stress can affect the ability of fish to respond to various stressors, such as pathogens or environmental variations. In this paper, the effects of social stress on gilt-head bream (Sparus aurata) were investigated. To study the effects of physiological stress, we evaluated biochemical and cellular parameters, such as cortisol, glucose, lactate, osmolarity, and phagocytosis, 24 h after the establishment of social hierarchy in a group of three fish. Social hierarchy was determined and characterized by behavioral observation (aggressive acts and feeding order) of the specimens (dominant: "α"; subordinate: "β" and "γ"). After the establishment of social hierarchy, we observed that, overall, levels of plasma cortisol and other biochemical plasmatic stress markers (glucose and lactate) were higher in subordinate individuals than in dominant individuals. In addition, the modulation of phagocytic activity of the peritoneal exudate cells (PECs) demonstrated that social stress appeared to affect immune response. Finally, principal component analysis clearly separated the subordinate fish groups from the dominant groups, based on stress markers and the phagocytic activity of peritoneal exudate cells. This study contributes to current knowledge on gilt-head sea bream, helping to understand the link between social stress, behavior, and physiology of this species, relevant in the aquaculture sector, where fish are subjected to several kinds of stress. [ABSTRACT FROM AUTHOR]

Simple Summary: Assessment of the energetic costs of different living activities is of primary interest among fish biologists. However, assessing energy expenditure in free-swimming fish is challenging owing to the difficulty of performing such measurements in the field. Therefore, the use of implant fish with sensors that transmit signals that serve as a proxy for energy expenditure is a promising method to counter these limitations, allowing remote monitoring in tagged fish. The aim of this study was to correlate the acceleration recorded by the tag with the activities of the red and white muscles and the oxygen consumption rate (MO2), which could serve as a proxy for energy expenditure, in gilthead sea bream (Sparus aurata), a key species in European marine aquaculture. The acceleration recorded by the tag was successfully correlated with MO2. Additionally, through electromyographic analyses, we determined the activities of the red and white muscles, which are indicative of the contributions of aerobic and anaerobic metabolisms during swimming. Finally, the tag implantation did not affect the swimming performance, metabolic traits, and swimming efficiency of the sea bream. By obtaining insights into both aerobic and anaerobic metabolisms, sensor mapping with physiological indicators may be useful for the purposes of aquaculture health/welfare remote monitoring of gilthead sea bream. Measurement of metabolic rates provides a valuable proxy for the energetic costs of different living activities. However, such measurements are not easy to perform in free-swimming fish. Therefore, mapping acceleration from accelerometer tags with oxygen consumption rates (MO2) is a promising method to counter these limitations and could represent a tool for remotely estimating MO2 in aquaculture environments. In this study, we monitored the swimming performance and MO2 of 79 gilthead sea bream (Sparus aurata; weight range, 219–971 g) during a critical swimming test. Among all the fish challenged, 27 were implanted with electromyography (EMG) electrodes, and 27 were implanted with accelerometer tags to monitor the activation pattern of the red/white muscles during swimming. Additionally, we correlated the acceleration recorded by the tag with the MO2. Overall, we found no significant differences in swimming performance, metabolic traits, and swimming efficiency between the tagged and untagged fish. The acceleration recorded by the tag was successfully correlated with MO2. Additionally, through EMG analyses, we determined the activities of the red and white muscles, which are indicative of the contributions of aerobic and anaerobic metabolisms until reaching critical swimming speed. By obtaining insights into both aerobic and anaerobic metabolisms, sensor mapping with physiological data may be useful for the purposes of aquaculture health/welfare remote monitoring of the gilthead sea bream, a key species in European marine aquaculture. [ABSTRACT FROM AUTHOR]

Simple Summary: Measuring metabolic rates in free-swimming fish would provide valuable insights about the energetic costs of different life activities this is challenging to implement in the field due to the difficulty of performing such measurements. Thus, the calibration of acoustic transmitters with the oxygen consumption rate (MO2) could be promising to counter the limitations observed in the field. In this study, calibrations were performed in rainbow trout (Oncorhynchus mykiss), and a subsample of fish was implanted with such a transmitter and then followed under aquaculture conditions. The use of acoustic transmitters calibrated with MO2 appeared to be a promising tool to estimate energetic costs in free-swimming rainbow trout, and for welfare assessment in the aquaculture industry. Metabolic rates are linked to the energetic costs of different activities of an animal's life. However, measuring the metabolic rate in free-swimming fish remains challenging due to the lack of possibilities to perform these direct measurements in the field. Thus, the calibration of acoustic transmitters with the oxygen consumption rate (MO2) could be promising to counter these limitations. In this study, rainbow trout (Oncorhynchus mykiss Walbaum, 1792; n = 40) were challenged in a critical swimming test (Ucrit) to (1) obtain insights about the aerobic and anaerobic metabolism throughout electromyograms; and (2) calibrate acoustic transmitters' signal with the MO2 to be later used as a proxy of energetic costs. After this calibration, the fish (n = 12) were implanted with the transmitter and were followed during ~50 days in an aquaculture facility, as a case study, to evaluate the potential of such calibration. Accelerometer data gathered from tags over a long time period were converted to estimate the MO2. The MO2 values indicated that all fish were reared under conditions that did not impact their health and welfare. In addition, a diurnal pattern with higher MO2 was observed for the majority of implanted trout. In conclusion, this study provides (1) biological information about the muscular activation pattern of both red and white muscle; and (2) useful tools to estimate the energetic costs in free-ranging rainbow trout. The use of acoustic transmitters calibrated with MO2, as a proxy of energy expenditure, could be promising for welfare assessment in the aquaculture industry. [ABSTRACT FROM AUTHOR]

Three groups of European sea bass (Dicentrarchus labrax) were fed for seven months, with either a conventional diet or two different organic diets, which contain organic vegetables and a natural antioxidant compound. The two organic diets differed themselves in terms of raw proteins, fish oil, and lipid contents. Sea bass welfare condition was assessed in relation to these three diets, using 16 different indicators. These were: swimming activity (recovery test, muscle activity), haematological and serological stress indicators (haematocrit, haemoglobin, red-blood-cell count, cortisol, glucose, lactate), aspecific immunity parameter (lysozyme), indicators of exposure to organic contaminants (7-ethoxyresorufin-O-deethylase and glutathione-S-transferase), and growth parameters (weight gain, specific growth rate, feed conversion ratio, protein efficiency ratio, and hepato-somatic index). Most of these parameters individually did not give consistent responses, but their integration can provide an accurate evaluation of the fish welfare conditions among the three diet experimental groups. The multiparametric approach outlined a comprehensive picture of sea bass physiological state. The principal component analysis and the multi-criteria-decision-analysis were found to be useful tools for an integrated fish welfare assessment, highlighting that the best welfare condition was achieved in the experimental group fed with the protein-rich organic diet. [ABSTRACT FROM AUTHOR]