Oxygen availability is a critical environmental factor influencing the physiology and behaviour of aquatic organisms. This study investigated the effects of chronic exposure to varying oxygen levels on the respiratory and locomotor behaviours of African catfish (Clarias gariepinus) juveniles (mean body mass: 92.0 ± 6.6 g).
Three groups of fish (n = 8 per treatment) were acclimated for 30 days to normoxic (6 mgL-1), moderately hypoxic (3 mgL-1), and extremely hypoxic conditions (<1 mgL-1). During acclimatization, the fish were hand fed three times daily at 3% of their body with a commercial feed. Following acclimation, air-breathing frequency, gill ventilation rates, and general swimming activity were assessed. Results showed that reduced oxygen levels elicited slight changes in air-breathing frequencies which were not statistically significant across treatments. The mean air-breathing frequencies ranged from a highest of 1.11±0.24 breaths min-1 in the normoxia group, followed by 0.90 ± 0.21 and 0.91 ± 0.18 breaths min-1 in the moderate hypoxia and extreme hypoxia groups respectively. Gill ventilation and swimming behaviours remained largely unaffected. These findings suggest that C. gariepinus juveniles exhibit a degree of behavioural resilience to chronic hypoxia, with limited adjustments in respiratory behaviour. This highlights the species’ adaptive potential to fluctuating oxygen environments, which is relevant for aquaculture systems and natural habitats increasingly affected by deoxygenation.