The impact and control of biofouling in marine finfish aquaculture

We review the impact and control of fouling of netting and cages in finfish aquaculture. The large surface area and structure of netting material, particularly multifilament mesh, is highly suitable for colonisation and growth of fouling. Furthermore, fouling growth is often rapid because the waters surrounding aquaculture operations are enriched by organic and inorganic wastes (uneaten food, faecal and excretory material) generated by high-density fish populations. Biofouling of fish-cage netting is a significant operational problem to aquaculture. The occlusion of mesh and the resulting restriction in water exchange adversely affects fish health by the reduction in dissolved oxygen (DO) and the accumulation of metabolic ammonia. Fouling is of further concern because it significantly decreases cage flotation, increases structural fatigue and cage deformation, and may act as a reservoir for pathogens. The impacts of fouling vary dramatically depending on season and location, and are also influenced by farming methods and practices. The impacts of these factors are reviewed and highlighted. The overall outcome is that there are few comprehensive quantitative studies of fouling or its impacts on sea-cage aquaculture, and this impairs the ability to develop the most appropriate mitigation strategies to control fouling. Effective fouling control is particularly difficult, given the high species diversity and spatial variation typical of many fouling communities on cages. However, the continual expansion of finfish aquaculture, in particular cage aquaculture into tropical regions where fouling is highly diverse with rapid year-round growth rates, is increasing demand for fish-cage antifouling technologies. At the same time, the control and regulation of products available for use in aquaculture, and the phasing out of many metal-based products, mean that there are fewer antifouling products available than there were a decade ago. We review the range of antifouling technologies currently available, including mechanical cleaning, coatings incorporating biocides, and their non-release alternatives. Recommendations for effective biofouling control and directions for future research are identified given the need to develop non-toxic coatings specifically suited for aquaculture applications