The present study is part of the PRIMA project Fish-PhotoCAT, which aims to evaluate the efficiency of a smart purification system in improving water quality, fish production, and environmental sustainability in aquaculture This system utilizes an innovative TiO2-based photo-electrocatalytic (PEC) filter for the remediation of nitrogen compounds in water. This new-generation, low-cost filter is developed from the traditional filters used in aquaculture, combining the purifying action of the TiO2 and the biocidal action of the UV. The efficiency of this filter will be tested in both freshwater and seawater RAS systems, where two important Mediterranean farmed fish species are reared: the rainbow trout and the gilthead seabream. Specifically, this preliminary study evaluated the effects of the PEC filter on the stress status of rainbow trout during the grow-out phase, measuring cortisol, the primary stress-related hormone in fish, in a suite of matrices to obtain a comprehensive assessment of both short- and long-term stress response.
The trial was performed at the Spallanzani Institute (Italy) where rainbow trout (IBW: 156±4.5g) were reared for four weeks at a low stocking density (15kg/m3) in six 500-L tanks equipped with either traditional UV-filter (CTRL; three tanks) or the PEC filter (PEC; three tanks). Prior to sampling, fish were euthanized with an overdose of anesthetic (MS222 Sigma-Aldrich), followed by spinal cord transection. Cortisol levels were measured in plasma, skin mucus, muscle, fin, and scales, using a specific microtitre radioimmunoassay (RIA). Statistical analysis was carried out using the T-test for body weight data and the Mann-Whitney U test for cortisol data with a significance level set at p < 0.05.
Fish body weight significantly increased during the trial, with no differences observed between the two systems (Table 1). Similarly, no differences were found in cortisol levels in any of the analyzed matrices, indicating that fish reared in the two systems exhibited a similar stress status. It is noteworthy that the measured cortisol levels were very low (Table 1) and comparable to the basal levels already reported for rainbow trout.
In conclusion, this innovative system was successfully tested in rainbow trout, with effectiveness assessed in terms of fish growth and stress response. Future investigations are planned to test this purification system in on-growing trout at a higher stocking density (30 kg/m3), during the juvenile phase, along with the selected seawater candidate, the gilthead seabream.