Biofouling is a serious problem in marine aquaculture facilities, exerting several negative effects on cage structures. In this study, different materials of nets were placed in the Fujian Sea area of China, and the main biological adhesion species were determined. The drag force of different materials of fouled nets was studied by a physical test in a flume tank. The drag force coefficient of a clean polyethylene terephthalate (PET) net was 0.53. The drag force coefficients of ultrahigh-molecular-weight polyethylene (UHMWPE) and polyethylene (PE) nets were 161.2% and 133.5% higher, respectively, compared with those of PET nets. Crustaceans, mollusks, and algae were the main organisms that adhered to the nets. Compared with the clean nets, the drag force of PET, UHMWPE, and PE nets increased by 1.29–5.06 times, 1.11–2.85 times, and 0.55–2.46 times, respectively. Based on backpropagation (BP) neural network training, the relationship between biological characteristics (average adhesion thickness and density) and the drag force of three kinds of net materials was determined. The drag force of the biofouled net at various time points throughout the year can be predicted based on this model, which can guide the cleaning and maintenance of nets in cage structures.

Biofouling on netting poses a significant challenge, as it can considerably increase the weight of the nets and shorten their service lifespan. This study investigates the properties of polyethylene-grafted poly(hexamethylene guanidine) (PE-g-PHMG) modified ultra-high molecular weight polyethylene (UHMWPE) monofilaments. The results show that the addition of PE-g-PHMG decreases the degree of crystallinity, average lattice spacing and crystallite size of the blend monofilaments, leading to relatively low rigidity and high toughness. The incorporation of PE-g-PHMG enhances both the knot strength (increased by 17.9%) and the overall antibacterial performance (efficacy rates of 99.4% and 97.2% against Escherichia coli and Staphylococcus aureus ) of the blend monofilaments. Furthermore, blend monofilaments (UHMWPE-20%) after washing 30 times exhibit high efficacy rates against E. coli and S. aureus . This article provides a method for preparing fishing grade polyethylene monofilaments that effectively combines favourable characteristics, including enhanced knot strength and good antibacterial properties.

Biofouling on aquaculture netting increases hydrodynamic drag and restricts water exchange across net cages. The solidity ratio is introduced as a quantitative parameter to characterize fouling severity. Towing tank experiments and computational fluid dynamics (CFD) simulations were used to assess the hydrodynamic behavior of netting under different fouling conditions. Experimental results indicated a nonlinear increase in drag force with increasing solidity. At a flow velocity of 0.90 m/s, the drag force increased by 112.2%, 195.1%, and 295.7% for netting with solidity ratios of 0.445, 0.733, and 0.787, respectively, compared to clean netting (S_n = 0.211). The drag coefficient remained stable within 1.445–1.573 across Re of 995–2189. Numerical simulations demonstrated the evolution of flow fields around netting, including jet flow formation in mesh openings and reverse flow regions and vortex structures behind knots. Under high solidity (S_{n =} 0.733–0.787), complex wake patterns such as dual-peak vortex streets appeared. Therefore, this study confirmed that the solidity ratio is an effective comprehensive parameter for evaluating biofouling effects, providing a theoretical basis for antifouling design and cleaning strategy development for aquaculture cages.