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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]

Coping style is defined as a set of individual physiological and behavioural characteristics that are consistent across time and context. In the zebrafish Danio rerio, as well as in many other animals, several covariations have been established among behavioural, physiological and molecular responses. Nonetheless, not many studies have addressed the consistency in behavioural responses over time starting at the larval stage. Therefore, this study aimed to improve the understanding of behavioural consistency across contexts and over time in zebrafish from the larval to juvenile stages. Two distinct experiments were conducted: a larval stage experiment (from 8 to 21 days post fertilization, dpf) and a juvenile stage experiment (from 21 to 60 dpf). On one hand, the larval experiment allows to focus on the transition between 8 and 21 dpf, marked by significant morphological changes related to the end of larval stage and initiation of metamorphosis. On the other hand, the juvenile experiment allows to properly cover the period extending from the end of larval stage to the juvenile stage (60 dpf), including metamorphosis which is itself completed around 45 dpf. Within each experiment, boldness was determined using a group risk‐taking test to identify bold and shy individuals. A novel environment test was then performed at the same age to evaluate consistency across contexts. Groups of fish (either bold or shy) were bathed in an alizarin red S solution for later identification of their initially determined coping style to evaluate behavioural consistency over time. Fish were then reared under common garden conditions and challenged again with the same behavioural tests at a later age (21 and 60 dpf in the larval and juvenile experiments, respectively). Behavioural consistency was observed across contexts, with bold fish being more active and expressing higher thigmotaxis regardless of age. There was, however, little behavioural consistency over age, suggesting behavioural plasticity during development. Moreover, the use of alizarin red S to conduct this experiment provides new perspectives for the further study of the longitudinal evolution of various traits, including behaviour, over life stages in fish. [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]

• Trout of different personality/competitive ability were exposed to aquaculture stressors (hypoxia and high ammonia). • Hypoxia resulted overall in reduced swimming activity, but induced no physiological stress. • High levels of ammonia were stressful, and induced an increase of avoidance behavior. • Personality-related behavioral differences were evident upon stress (high ammonia). • The data support the use of wireless accelerometer sensors as a promising tool for welfare monitoring in aquaculture. As other vertebrates, fish differ on an individual basis in their responses to disturbance (i.e. stress) and in their capacity for adaptation to environmental change. This individual stress-coping style (SCS) might have an impact on the individual welfare in aquaculture facilities. However, most of the studies about the behavioral and physiological stress responses of fish with different SCS were performed under conditions very unlike usual rearing conditions. Therefore, we aimed in the current study at investigating the behavioral and physiological responses of rainbow trout (Oncorhynchus mykiss) of different SCS to common aquaculture stressors (exposure to hypoxia or high ammonia) under realistic conditions. We first screened the fish according to their competitive ability, as a proxy of SCS, separating the best and worst competitors (winners, W, and losers, L, respectively). Then, we evaluated the behavioral (using both telemetric and video-monitoring approaches) and physiological response of both groups upon exposure to increasing levels of hypoxia and ammonia. Overall, increasing hypoxia induced a slight but progressive decrease in fish activity, independently of the fish SCS. High concentrations of total ammonia induced an increase of certain behavioral displays, such as swimming bursts or approaches to the surface, the latter being overall more frequent in W than in L fish. At the specific stress levels tested (hypoxia: 50 % oxygen saturation; total ammonia: 2.91 mM), the physiological stress markers showed that the behavioral response to ammonia was probably driven by stress, while the behavioral response of the fish to hypoxia was just a behavioral adjustment to accommodate the decrease in oxygen availability. In conclusion, our data show that fish of different competitive ability showed similar activity patterns in routine conditions or when adapting to non-stressful conditions (50 % oxygen saturation) in an aquaculture-like setup, but differed in their behavioral response when exposed to stress (high water ammonia). In addition, our data support the use of acoustic accelerometer transmitters as a promising tool for real-time monitoring of fish welfare in commercial fish farms. [ABSTRACT FROM AUTHOR]