Nano-engineering of a thermoplastic compound with CuO nanoparticles for the development of safe antimicrobial and anti-biofouling fish cage nets

The occurrence of biofouling is the most common problem that may arise on the surface of fish cage nets in freshwater and the marine environment. The issue not only induces structural damage to the netting because of the progressive increase in weight but also reduces the freshwater exchange and oxygen flow inside the cage, possibly leading to health problems for the farmed fish. Regular cleaning or inclusion of anti-fouling agents in the fish net cage material are typical methods to avoid biofouling growth and proliferation. Both are considered costly and pose health and environmental risks. In this study, a nano-engineered approach was adopted by embedding antimicrobial copper oxide (CuO) nanoparticles in the polyamide net fibers in order to prevent biofouling. The nano-engineered fish cage nets showed a strong anti-microbial effect, with up to a 6-log reduction of <i>S. aureus</i> and a 3-log reduction of <i>E. coli</i> in simulated seawater. Moreover, fine-tuning of the polyamide crystallinity level allowed for minor, within the range of 0.009 mg L^-1 to 0.06 mg L^-1, leaching of CuO nanoparticles into the aquatic environment. Aquatic toxicity, assessed in freshwater by monitoring mortality, malformations and hatching rates in zebrafish embryos exposed to different dilutions of samples leachates, over a 96 hour post-fertilization period, demonstrated a dose- and manufacturing-dependent embryotoxic effect, highlighting the importance of early-stage nanomaterial safety evaluation.