DNA and chromosomal damage in Senegalese sole (Solea senegalensis) as side effects of ozone-based water treatment - Contribution to optimization of fish-farming practices.

The progressive growth of aquaculture implicates a dependence on large water amounts, which are submitted to disinfection processes, namely ozonation. Considering the importance of genomic integrity, it is critical to improve the knowledge on ozone-related genotoxic hazard to organisms reared in recirculating aquaculture systems (RAS) applying ozonation. Therefore, genetic damage induced by ozone exposure in the Senegalese sole (Solea senegalensis) was assessed, combining the comet and the erythrocytic nuclear abnormalities (ENA) assays, reflecting different damage levels, i.e. DNA and chromosomal damage, respectively. Fish were subjected to a daily 6-h ozone (0.15 mg L-1 ) exposure, repeated for 3 consecutive days, simulating a short-term event of overozonation. To assess the temporal impact of the previous event, the progression of damage was evaluated 7 days later, following transference to ozone-free water or to 0.07 mg L-1 ozone, a routinely adopted level in RAS. Both endpoints pointed to the ozone genotoxic potential, displaying DNA oxidation as a possible mechanism of damage. Overall, the present findings pointed out the genotoxic hazard of ozone to fish, highlighting the importance of these types of studies and contributing to improve aquaculture practices, namely in RAS systems. These early genotoxic signals may be a prelude to negative repercussions on fish health, which may affect the aquaculture productivity. The present findings recommend precautions in relation to accidental or intentional overozonation in fish-farming, even when short-term events are considered. The strategies to mitigate the impact of ozonation in S. senegalensis may include a dietary extra supplementation of antioxidants (regularly, or punctually in cases of overozonation).