Behavioural Response Detection in Nile Tilapia, Oreochromis niloticus (Linnaeus, 1758) With Different Formalin Concentrations Using Tracker Software-Based Computer Vision Techniques

Changes in fish behaviour caused by stress are difficult to measure. In this study, tracker software-based computer vision techniques were applied, with formalin used as a stressor. At different formalin concentrations, stress responses of Nile tilapia, Oreochromis niloticus (Linnaeus, 1758), were examined for fish swimming velocity (FSV) and behaviour. Seven treatments included 1 (control) without formalin, with treatments 2–7 consisting of 100, 200, 300, 400, 500 and 600 mg.L-1formalin concentration, respectively. Three (25 × 51 × 31 cm, width × length × height) glass tanks were 80 % filled with water for each trial. Each tank contained three fish with weights of 0.5–1.0 g, and the FSV of each fish was recorded for 120 min after exposure to formalin. Average FSV statistically differed (P < 0.05) at different formalin concentrations. Treatment 1 (control) gave the highest FSV at 0.038 ± 0.005 m.S-1 followed by treatments 2 (100 mg.L-1) and 3 (200 mg.L-1) at 0.020 ± 0.013 and 0.018 ± 0.020 m.S-1, respectively. Treatments 4 (300 mg.L-1), 5 (400 mg.L-1), 6 (500 mg.L-1) and 7 (600 mg.L-1) recorded 0.007 ± 0.010, 0.006 ± 0.090, 0.004 ± 0.008 and 0.003 ± 0.007 m.S-1, respectively. Differences in FSV at each concentration interval were applied to indicate the behavioural expression of fish response to stress in phase III (tertiary responses). Results indicated that computer vision techniques were suitable for studying Nile tilapia behaviour, with possible applications in other aquatic animals. Highlights of this technique included continuous real-time results to monitor fish stress using a non-invasive method.