Osmoregulatory cost of Nile tilapia across salinity gradients on growth and oxygen consumption rates

ABSTRACT

Nile tilapia (Oreochromis niloticus) exhibits remarkable phenotypic plasticity, particularly regarding its adaptability to varying environmental salinities. This study aimed to comprehensively evaluate the bioenergetic costs and rearing performance of Nile tilapia subjected to a micro-salinity gradient. A 30-day in vivo experiment was conducted at the Aquaculture Laboratory and Experimental Ponds of Universitas Sriwijaya. The study used a completely randomized design comprising five salinity treatments: P0 (0 ppt; freshwater control), P1 (1 ppt), P2 (2 ppt), P3 (3 ppt), and P4 (4 ppt). The result showed that an optimal survival rate was recorded at 1 ppt (P1; 85%), contrasting sharply with the lowest survival observed in the freshwater control (P0; 35%). Conversely, somatic growth peaked at 2 ppt (P2), yielding the highest absolute weight gain (13 g), while the maximum length extension (3 cm) was co-dominantly observed in the 2 ppt and 3 ppt treatments. Interestingly, despite recording the lowest survival, the highest feed efficiency was maintained in the control group (P0; 48.43%). Furthermore, the metabolic cost of osmoregulation peaked at 3 ppt (P3), as evidenced by the maximum oxygen consumption rate (0.26 mg O₂ g⁻¹ h⁻¹). Overall, the data suggest that low-to-moderate salinity levels (1–2 ppt) provide a substantially more optimal rearing environment compared to strictly freshwater or higher salinity conditions. Operating within this micro-salinity range effectively balances osmoregulatory energy expenditure with maximized growth and survival rates, offering strategic bioenergetic insights for sustainable tilapia aquaculture operations.