Stress and growth biomarkers in adult rainbow trout (

Introduction: The present study is part of the PRIMA Fish-PhotoCAT project, which aims to evaluate the effectiveness of a smart purification system for improving water quality, fish production, and environmental sustainability in aquaculture. The system employs an innovative TiO Methods: Adult rainbow trout were reared at low (LD, 15 kg/m Results: Cortisol concentrations in all sampled matrices did not differ significantly between CTRL and PEC groups at either stocking density. Similarly, plasma glucose, lactate, and TP remained unchanged between treatments. Hepatic expression of IGF-I, HSP70, and CYP1A1 also showed no significant differences. The AOPP/TP ratio was comparable between groups, although AOPP concentrations were higher in the PEC group under HD conditions. Despite this increase, cortisol values remained within physiological ranges, indicating no evidence of marked stress. Discussion: The PEC water treatment system provided rearing conditions comparable to conventional filtration with respect to physiological, biochemical, and molecular stress responses in adult rainbow trout. The absence of treatment-related changes in cortisol, metabolic indicators, and stress-related gene expression suggests that PEC technology does not compromise fish welfare under the tested conditions. However, the increase in AOPP observed at high stocking density indicates a potential oxidative response that deserves further investigation. Overall, these findings support the use of PEC technology as a sustainable water treatment strategy for aquaculture while maintaining fish health and welfare.