Environmental Management of Fish Cage Aquaculture

Abstract

Most modern fish culture involves the intensive input of nutrients in the form of feed, yet only a small proportion of these nutrients is converted into the target product; they can be largely lost to bacterial degradation. However, when compared with other livestock production systems, aquaculture has better feed conversion efficiency and feed conversion ratios (FCRs) are continuing to improve. High levels of nutrients from fish cages may cause eutrophication and thus may affect fisheries adversely, but on the contrary, the additional nutrients from the feed may have a beneficial effect, boosting natural productivity including fisheries. The important components of fish farming waste comprise nutrients (dissolved and particulate) resulting from the metabolism of fish food, uneaten food, escapees of farmed fish affecting the genetic diversity of wild fish populations and chemical residues of disease or parasitic therapeutant treatments. Potential management measures to mitigate environmental impacts include public and private sector approaches. The public sector approaches include appropriate and specific aquaculture policies, strategies, regulations, legislation, and management plans, adoption and implementation of the FAO Code of Conduct for Responsible Fisheries (CCRF) and Ecosystem Approach to Aquaculture (EAA) strategies for planning, management, monitoring, and control. Zoning for aquaculture space is to be based on the allocation of aquafarms on suitable areas, appropriate evaluation of carrying capacity of the ecosystem, planning and management for disease prevention and treatment and environmental control. Appropriate control of farm permits, licences, and registration by the state is necessary to monitor and control aquaculture development. The private sector approaches include improved feed formulation and feeding strategies to reduce the feed conversion ratio and nutrient losses, the use of Integrated Multi-trophic Aquaculture (IMTA) to utilise nutrient outputs from intensive aquaculture and thus regular environmental monitoring is the key to ensure that impacts remain within acceptable limits.