This study explored the innovative application of photoelectrocatalysis (PEC), an advanced evolution of conventional photocatalysis, as a water remediation technology in recirculating aquaculture systems (RASs) for adult rainbow trout ( Oncorhynchus mykiss , 150–200 g). The research focused on its impact on fish muscle and skeletal health using a multidisciplinary approach. Water quality parameters were registered and monitored, including nitrate, nitrite, and ammonia concentrations, and calcium content was measured at the end of the 1‐month trial. To identify potential skeletal anomalies, imaging analyses including X‐ray and computed tomography (CT) were performed. Additionally, histochemical analysis with Picrosirius Red (PSR) staining was used to evaluate collagen distribution in the vertebrae. Muscle density was assessed by CT scans and histological analysis to study metabolism and the size/diameter of white muscle fibers. Finally, genes related to myogenesis and antioxidant enzymes were studied to detect muscle growth and oxidative stress, respectively. The PEC showed lower nitrite and nitrate levels and higher dissolved oxygen (DO) compared to the control (CTR), likely due to photoelectrocatalytic activity, with overall more stable water chemistry. At the end of the trial, a reduction in calcium content in the water was observed ( p < 0.05), without affecting the calcium content in the vertebral bones. Skeletal analyses revealed no anomalies, and collagen distribution in the bone matrix appeared normal. Muscle morphology indicated proper development, with a slight hypertrophic trend in the PEC group. Oxidative stress analysis suggested no adverse effects from PEC treatment, as antioxidant enzyme levels were similar between groups. In summary, the absence of skeletal anomalies and adequate muscle growth, associated with the improvement of water quality in the PEC, suggests that this new remediation technology is a valid, sustainable aquaculture approach, combining environmental innovation and fish health.

Aquaculture has rapidly expanded, surpassing capture fisheries and playing a vital role in global food security. However, this growth raises environmental concerns, especially regarding nitrogen waste accumulation in recirculating aquaculture systems (RASs). Nitrogen compounds from uneaten feed and fish excreta, mainly ammonia (NH₃) and nitrite (NO₂⁻), lead to water pollution, eutrophication, and greenhouse gas emissions. This study describes the setup and the efficiency of a new photo-electrocatalytic (PEC) system in reducing nitrogen waste in a high-density RAS for rainbow trout (30 kg/m³). The PEC system, an evolution of a pure photocatalytic system, was integrated in the units of the RAS and tested for the first time in field conditions, combining photocatalysis and electrochemical oxidation to convert toxic nitrogen species (NH₃) into less harmful nitrogen forms (NO₃⁻ and N₂), aiming to mitigate both water and atmospheric pollution. Over a 4-week period, water nitrogen compounds, ammonia and greenhouse gases (carbon dioxide, nitrous oxide and methane) emitted by water were continuously monitored in two groups of three tanks (PEC vs. control). Each tank was equipped as an independent RAS unit. PEC treatment led to significantly lower NH₃ concentrations (0.96 ± 0.2 mg/L vs. 1.78 ± 0.2 mg/L, p < 0.01), lower NO₂⁻ levels and higher NO₃⁻ levels (61.77 ± 2.14 mg/L vs. 53.10 ± 2.14 mg/L, p < 0.01) in water, indicating efficient nitrogen oxidation. Gaseous emissions were also reduced: NH₃ (1.49 vs. 2.64 mg/m²/day, p < 0.05) and N₂O (1.44 vs. 2.88 mg/m²/day, p < 0.05). These results support PEC technology as a promising solution for improving nitrogen management in intensive aquaculture. Although challenges remain in optimizing energy use and scalability, PEC offers a valuable strategy for reducing environmental impact while sustaining productivity in the aquaculture industry.