fish and other marine creatures. The impacts of aquaculture on the environment are an increasingly important issue as aquaculture operations expand globally. These impacts are largely dependent on the intensity of production, the species farmed and the farm location[sc:1].
Negative impacts of aquaculture on the environment
In South-East Asia where finfish and shellfish are heavily produced and poorly managed there are fairly heavy environmental impacts. Finfish production here is usually quite intensive and involves an addition of solids and nutrients to the marine environment to help fish grow. This process is generally recognised as being potentially degrading to the environment as such a rapid unnatural build-up of organic material can negatively impact on the localised flora and fauna. In some cases this can cause major changes to the sediment chemistry and affect the overlying water column location[sc:1].
The effect of farmed fish on local wild fisheries is also a real environmental concern in South-East Asia and elsewhere. Outbreaks of disease from farms can spread quickly due to the high concentrations in which fish are retained and is easily spreadable into wild fish populations if uncontrolled. Aquaculturalists used to tackle these outbreaks with antibiotics in fish feed until concern mounted over the effect of the drugs on local aquatic ecosystems as well as on consumers. Vaccinations are however now readily available for farmed fish and the practice of using drugs to tackle disease is seldom used in Western aquaculture[sc:2].
Additional impacts related to aquaculture may also occur as a result of other farm discharges and waste products. These can include from shore-based stun and bleed operations, the escaping of non-resident species, transmission of disease and (lack of) control of predatory species. Where species such as shellfish compete with other organisms such as native seagrass for survival, displacement can occur which has a potentially spiralling effect on the native wildlife[sc:1][sc:comma][sc:2].
Positive impacts of aquaculture on the environment
Despite a negative outlook there are some fairly positive environmental impacts to be recognised from aquaculture. These can be found in (artificially or naturally) nutrient enriched areas where the farming of filter feeders such as shellfish improve water quality. Farmed fish are also generally free of environmental contaminants such as mercury and heavy metals as they exclusively eat human-processed feed of which toxin levels are regulated[sc:1][sc:comma][sc:2].
Room for improvement
Achieving the sustainable use of aqua-cultural techniques and aquatic ecosystems has the predominant objective of fisheries managers for decades; however it has arguably failed due to lack of governance. Natural variability and climate change have also had significant implications for the productivity and management of aquaculture and catastrophic natural events continue have significant impacts on resources, infrastructures and people[sc:3].
Understanding, predicting and accounting for this is going to a significant challenge for the next decade[sc:3]. Aquaculture can be made more sustainable by producing the fishmeal and fish oil used in feeds from seafood waste. This type of recycling in the feed industry has been on the rise in recent years[sc:2]. Regulatory bodies have also recognized the problems with algae blooms and implemented measures to prevent them such as the use of cages to wash away effluent in locations where strong currents are existent[sc:2].