Mapping the Energetic Costs of Free-Swimming Gilthead Sea Bream (Sparus aurata), a Key Species in European Marine Aquaculture

European seabass show variable responses in their group swimming features after tag implantation

The usefulness of acoustic telemetry on the study of movements, interactions, and behaviors has been revealed by many field and laboratory studies. The process of attaching acoustic tags on fish can, however, impact their physiological, behavioral, and growth performance traits. The potential negative effects are still unknown for several species and behavioral attributes. Previous studies have attempted to shed light on the effects of tag implantation on fish, focusing mainly on fish growth and physiological parameters, and one or two behavioral properties mainly on the individual level. However, the effect of this procedure could also be expressed at the group level. This study investigated the short-term effects of dummy and active body-implanted acoustic tags on the group-level swimming performance of adult European seabass (Dicentrarchus labrax) using optical flow analysis. We studied four main swimming performance properties—group speed, alignment (polarization), cohesion, and exploratory behavior. To help in the interpretation of any detected differences, physiological stress-related parameters were also extracted. The results show that the tag implantation procedure has variable effects on the different swimming performance attributes of fish. Group cohesion, polarization, and the group’s exploratory tendency were significantly impacted initially, and the effect persisted but to a lesser extent two weeks after surgery. In contrast, group speed was not affected initially but showed a significant decrease in comparison with the control group two weeks post-surgery. In addition, the physiological parameters tested did not show any significant difference between the control and the treated group 14 days after the onset of the experiment. The findings suggest that the effect of tagging is non-trivial, leading to responses and response times that could affect behavioral studies carried out using acoustic telemetry.

Investigating the physiological response and antibody concentration of gilthead sea bream (Sparus aurata) following Vibrio anguillarum vaccination depending on the stress coping style

Stress coping styles (SCSs) are defined as coherent sets of individual physiological and behavioral differences in stress response consistent across time and context and are described in a wide range of taxa, including fishes. These differences in behavior and physiology are of great interest because they may have direct implications on animal health, welfare, and performance in farming systems, including aquaculture. In this study, the physiological responses of sea bream (Sparus aurata) from different SCSs following Vibrio anguillarum vaccination were monitored. Fish were first screened either bold or shy (proxy of proactive and reactive SCSs, respectively) using group risk-taking tests and were then injected with a vaccine against V. anguillarum. Following vaccination, the fish were implanted with an accelerometer tag to monitor their swimming activity (proxy of energy expenditure), and blood sampling was carried out to measure health and welfare parameters (e.g., cortisol, glucose, hemoglobin) and aspecific immunity (e.g., protease, total proteins). In addition, blood was also collected at three different sampling times to screen antibody levels and, thus, to evaluate the efficiency of the vaccine. Following vaccination, bold fish displayed lower swimming activity values, indicative of lower energy expenditure, and also displayed higher levels of hematocrit, total proteins, and lysozyme in the plasma than the shy ones, which could be indicative of better health/welfare status and greater aspecific immunity. Finally, the V. anguillarum vaccination appeared to be more efficient in bold fish since the number of total antibodies was found higher than in shy fish 1 month after vaccination. Such results could help improve both health/welfare and productivity of farmed sea breams by selecting more robust fish, better adapted to farming conditions.

Using Telemetry Sensors Mapping the Energetic Costs in European Sea Bass (Dicentrarchus labrax), as a Tool for Welfare Remote Monitoring in Aquaculture

Physiological real-time monitoring could help to prevent health and welfare issues in farmed fishes. Among physiological features that can be of interest for such purposes, there is the metabolic rate. Its measurement remains, however, difficult to be implemented in the field. Thus, mapping the fish acceleration recorded by tag with the oxygen consumption rate (MO2) could be promising to counter those limitations and to be used as a proxy for energy expenditure in the aquaculture environments. In this study, we investigated the swimming performance (Ucrit) and the swimming efficiency (Uopt, COTmin), and we estimated the metabolic traits (standard and maximum metabolic rates, SMR and MMR, as well the absolute aerobic scope, AS) of European sea bass (Dicentrarchus labrax; n = 90) in swimming tunnel. Among all tested fish, 40 fishes were implanted with an acoustic transmitter to correlate the acceleration recorded by the sensor with the MO2. In this study, the mean SMR, MMR, and AS values displayed by sea bass were 89.8, 579.2, and 489.4 mgO2 kg−1 h−1, respectively. The Uopt and COTmin estimated for sea bass were on average 1.94 km h−1 and 113.91 mgO2 kg−1 h−1, respectively. Overall, implantation of the sensor did not alter fish swimming performance or induced particular stress, able to increase MO2 or decrease swimming efficiency in tagged fish. Finally, acceleration recorded by tag has been successfully correlated with MO2 and fish mass using a sigmoid function (R2 = 0.88). Overall, such results would help for real-time monitoring of European sea bass health or welfare in the aquaculture environment in a framework of precision livestock farming.