Monitoring fish welfare is of paramount importance in aquaculture from an ethical, legal, and economic perspective. The development of new technologies such as cameras, implant tags, and various types of loggers could allow efficient and timely monitoring in real time, ensuring the welfare of the farmed animals. In this study, we experimentally tested the effect of repeated stress on established welfare indicators while also including the application of a previously developed camera-based welfare monitoring technology. Specifically, we induced change in welfare as crowding-induced stress and then recorded and analyzed fish behavior. Physiological and growth markers as well as visual cues were used to determine the levels of stress and access shifts in welfare while the repetition of the stress protocol was done to assess the habituation of the fish.
A trial was performed in a Recirculating Aquaculture System where juvenile European seabass of approximately 250 g were subjected to a protocol of repeated stressing, induced via crowding, at intervals of 15 days over a two-month period. Over this period, growth performance was monitored (weigh measurements, FCR) along with visual inspection for external abnormalities (ulcers, scales, fins, and tail issues). At sampling points, blood was collected, and cortisol measurements were used to quantify stress levels. For the duration of the trial, the behavior of the fish was recorded via ip cameras and behavioral indicators such as the speed were analyzed via methodology previously developed
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There were no significant differences between the control and the stressed groups in terms of growth with both groups increasing in weight by 150 g by the end of the trial. Similarly, baseline cortisol levels did not differ between the groups, exhibiting low stress values within the typical seasonal range at approximately 200 mg/ml. However, there were slight differences in conversion efficiency, with the stressed group exhibiting higher FCR values overall. Moreover, the prevalence of external abnormalities differed between stressed and non- stressed groups, with the former exhibiting higher, and increasing over time, frequency of visual cues compared to the control group. Regarding behavior, preliminary results suggest that there are no significant differences in the speed caused from the stressor. The stressed group appeared to have a lower swimming speed than the control group, but this difference was apparent throughout the whole experimental period, even before any stressor was applied. After the stressor applied, the difference between the control and the stressed group increased slightly. This could possibly indicate a weak effect of the stressor on the behavior of the treated group. These results highlight the importance of incorporating multiple indicators in the overall welfare assessment of farmed fish.
Georgopoulou, D.G., Vouidaskis, C., Papandroulakis, N., 2024. Swimming behavior as a potential metric to detect satiation levels of European seabass in marine cages. Front. Mar. Sci. 11:1350385. doi: 10.3389/fmars.2024.1350385