Introduction
The well-being of farmed fish significantly affects aquaculture productivity and profitability. Changes of environmental factors such as water temperature (T) and dissolved oxygen (DO) can directly impact fish energy demands and swimming performance, thus affecting overall health and growth. Technological advancements like cameras and environmental sensors offer promising opportunities for real-time fish welfare monitoring. This study examines the impact of water temperature on European seabass swimming performance in cages during the summer of 2023 when a heat wave occurred in Greece, compared to the relevant period in 2022, focusing on swimming speed as the behavioral variable.
Materials and methods
A group (N = 22,500 individuals) of E. seabass fish was reared during the two studied periods at the pilot scale netpen cage farm of HCMR at Souda bay, Crete (certified as an aquaculture facility from the national veterinary authority; code GR94FISH0001). Rearing was performed in circular polyester cages (40 m diameter, 9 m depth). A submerged network camera (Fyssalis V3.1) capturing at 10 fps was used for monitoring and video recording during daylight hours constantly for a period of two years, i.e. 2022 and 2023 . The camera was positioned at 4 m depth using a gyroscopic gimbal stabilizer to ensure its orientation remained directed upwards. We trained YOLOv5 (a machine learning model for object detection) to detect fish and adapted Deepsort (a model for tracking people) to track fish individually (using OPENCV/Python) and extract their speed. Bioceanor real time data logger (Aquabox) with T, DO, pH sensors (AquaTroll 500) were also deployed in the cage at 1m depth continuously collecting data. All data were transferred using multiple protocols (MQTT, HTTP) to the Aquareal platform. The mean weight of the fish ranged from 170 gr in March 2022 to 500 gr in September 2023. We tested for differences in the speed between years and between different temperatures.
Results
An increase in the environmental parameters was observed in summer 2023 and temperature increased from T2022 = 24.80 ± 0.57 °C to T2023 = 25.38 ± 0.63 °C (fig.1). Similar trend appeared in the fish speed as the average speed increased 0.08 b/sec (s2022 = 0.38±0.17 bd/sec and s2023 = 0.46±0.09 bd/sec). Figure 1 shows how the speed and the temperature (averaged values) varied within a day for both years. The fish showed the highest activity in the morning in both, 2022 and 2023. However the duration of the morning excitation lasted longer (apx. 2 hours longer) in 2023 than in 2022. In addition, there is a second excitation peak that appeared in 2023 at around 16:00 in the afternoon, and this peak coincides with the maximum peak the temperature had (25.71 °C).
Conclusion
From the preliminary results showed here, we can confirm that during the 2023 heatwave there was a change in the activity profile of the fish. Overall, the fish seem to show higher activity as they show higher average speed but also higher duration of increased activity. Previous studies have highlighted the varying energy demands of fish across different temperature ranges, underscoring the intricate relationship between environmental conditions and metabolic processes. Given the multifaceted implications of environmental conditions on fish welfare, continued research in this domain is essential.
Acknowledgement
This work has received funding from the European Union’s Horizon 2020 Research and innovation programme under grant agreement 101084204 (CURE4AQUA).
References
Barreto, M.O., Planellas, S.R., Yang, Y., Phillps, C., Descovich, K. Emerging indicators of fish welfare in aquaculture. Reviews in aquaculture 14, 343-361. https://doi.org/10.1111/raq.12601
Georgopoulou, D.G, Vouidaskis, C. and 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