Dynamics of endogenous and water cortisol release in Asian Sea bass Lates calcarifer after acute stress in a farm scale recirculating aquaculture system

Stress in farmed fish is associated with poor feeding, slow growth, disease, and mortality. Therefore, it is essential to closely monitor stress levels in fish to optimize farming practices, which could then enhance productivity and welfare in aquaculture operations. Cortisol, a circulating stress hormone, is a reliable biomarker for evaluating fish stress. As blood sampling is highly invasive, alternative cortisol sampling methods such as fin, mucus, and the surrounding water that contains released cortisol, have been proposed as less invasive or non-invasive sampling methods. However, a comprehensive understanding of their temporal dynamics and associations with plasma cortisol levels is still lacking. In this study, we subjected Lates calcarifer, Asian sea bass within a farm-scale (3000 L tank, 9000 L system) and high-flow rate (8000 L/h) Recirculating Aquaculture System (RAS) to an acute handling stress challenge involving chasing and air exposure, and quantified cortisol dynamics within different biological samples, including blood, fin, and mucus, and in tank water from multiple sampling points. We showed that handling stress induced an expected increase in plasma and mucosal cortisol, peaking at 1 h and 24–48 h, respectively, and that plasma and mucosal cortisol were moderately correlated, especially during the stress period. Fin cortisol did not show consistent dynamics. Water cortisol similarly rose, but peaked within 40 min from the start of the stressor, in a pattern that was dependent on the site of sampling within the RAS system, likely due to RAS circulation dynamics. Our study is the first to examine the impact of stress on cortisol accumulation and release in Asian Sea bass in a farm-scale RAS, thus complementing existing research on the efficacy of fin, mucus, and water cortisol as stress indicators that could help optimize aquaculture productivity and welfare. •Plasma and mucosal cortisol are elevated following chasing and air exposure stress in Asian sea bass (Lates calcarifer).•Plasma and mucosal cortisol are correlated but increase along different time courses.•Water cortisol in a farm-scale, high-flow rate RAS showed a faster peak with different dynamics across RAS compartments.•Water cortisol may be a reliable stress indicator in farm-scale RAS across varying stocking densities and conditions.