Evaluating metabolic rate and specific dynamic action in recirculating aquaculture systems: Influence of stocking density and feeding level in barramundi (Lates calcarifer)

Bioenergetic modelling plays a crucial role in aquaculture, optimizing nutrition, growth prediction, husbandry, and genetic management. The estimation of animal metabolic rate (MR), traditionally conducted in closed respirometric chambers, is a fundamental aspect of these models. This study presents a novel method for directly measuring fish MR, routine metabolic rate (RMR), postprandial peak metabolic rate (PMR), and specific dynamic action (SDA) parameters including SDA coefficient (C_SDA) within a recirculating aquaculture system (RAS). Additionally, the study evaluates the effects of fish size, stocking density, and feeding levels on these metabolic metrics. Using 3510 barramundi (Lates calcarifer, 51.2 g) housed in 27 RAS tanks (1 m³, 30.0 °C seawater), dissolved oxygen levels every 10 min for 56 days to model metabolic parameters. Fish MR ranged from 14.5 to 112.8 mg O₂ fish⁻¹ h⁻¹, following a daily sinusoidal pattern. PMR fit a power model (PMR = 2.18 × body weight [BW]^0.71, R² = 0.70, n = 810), while RMR followed an exponential model (RMR = 6.31 × exp. (0.01 × BW), R² = 0.87, n = 148). SDA parameters remained largely unaffected by stocking density or feeding rate (P > 0.05), with time-to-peak = 8.8–10.7 h, total SDA duration = 22.1–22.6 h, SDA factual scope = 2.0–2.9, and C_SDA = 14.8–16.4 %. Although this RAS-based methodology does not match the precision of closed-chamber respirometry, the results closely align with previous findings. This approach therefore provides a scalable tool for phenotyping metabolic variations in commercial aquaculture.