Effectiveness of several commercial non-toxic antifouling technologies for aquaculture netting at reducing mussel biofouling

Biofouling causes a range of problems in aquaculture, and there is a need to validate the effectiveness of antifouling products marketed in the industry. We tested the antifouling performance of four commercial aquaculture netting options at a trout aquaculture operation in the Bras d'Or Lakes, Nova Scotia, Canada. This site has brackish water and a severe mussel (Mytilus edulis) biofouling problem – complete net occlusion can occur within four weeks of the onset of mussel larvae settlement. We tested white and black nylon netting as controls, and four products marketed as having non-toxic antifouling properties: white and black Finsulate®, white Netminder® coating on white nylon netting, and white Dyneema® netting. In 2017, using image analysis measurements of fouling, we found only Netminder® significantly delayed fouling by two weeks over controls. Nonetheless, biofouling on all netting treatments (a mixture of filamentous algae and mussels) reached saturation (i.e. complete net occlusion in the images) within six weeks. After 17 weeks, the Netminder® coated netting supported significantly greater mussel biomass (measured by shell masses). In 2018, a follow-up experiment found that Netminder® caused a one-week delay in exclusively mussel biofouling compared to the white nylon control netting. We conclude that none of the options tested are likely to reduce severe mussel biofouling substantially. However, the benefits of a one-to-two week delay in biofouling caused by Netminder® (including reduced cleaning costs and diminished influence of mussels on water properties and the benthos under the net pens) should be weighed against the cost of application and maintenance for the coating.