Effect of different aquaculture systems on chronic hypoxia tolerance in Nile tilapia, Oreochromis niloticus: growth rate, physiological responses, oxidative stress biomarkers, and flesh quality

This study aims to evaluate the effect of rearing systems, traditional aquaculture system (TAS) and recirculating aquaculture system (RAS), on the ability of Nile tilapia, Oreochromis niloticus, to tolerate chronic hypoxia, growth, hemato-biochemical and oxidative stress biomarkers, and flesh quality parameters. The study consists of two parts, the first involves rearing fish under TAS and RAS in three replicates for 60 days. Nile tilapia fingerlings (initial weight 41.59 ± 5.21 g) were stocked at 4.15 ± 0.61 kg m^–3 in both systems. The second part is a chronic hypoxia test (dissolved oxygen = 1.0 ± 0.2 mg L^–1) in three replicates for 10 days at a stocking density of 7.60 ± 0.36 kg m^–3, followed by a recovery period of 48 h. Fish reared in RAS outperformed (P < 0.0001) TAS in terms of weight gain by 49.57%. Hypoxic fish in both systems exhibit behavioral and morphological changes, which are more rapid in appearance and severe in TAS compared to RAS. Serum cortisol and glucose levels raised significantly (P ≤ 0.05) in both treatments indicating stress, but return to normal levels after the recovery period. Hematological parameters, AST activity, serum proteins, total antioxidant capacity, and superoxide dismutase activity of fish reared in TAS were significantly (P ≤ 0.05) lower in most sampling times. Flesh quality parameters in TAS-reared fish were significantly (P ≤ 0.05) deteriorated than those reared in RAS at all-time intervals. In conclusion, fish reared in RAS experienced superior growth performance, better tolerance to chronic hypoxia, health status, and flesh quality compared to TAS.