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Aquaculture: Aquaculture and the Environment |
| What DLIST users say…” Aquaculture has a problem of that, it leads to the destruction of sensitive ecosystems to make way for land based fish farms, particularly the destruction of mangroves and coastal forest to farm shrimp and prawns” |
 There is considerable debate over the environmental impacts of aquaculture, which have cast doubts on the industry’s claims of sustainability. Some of the main issues raised are:
- Positioning of fish farms often block access to coastal areas that were once common land in use by many people. Due to alack of formalised land rights and entitlements in such areas, this could lead to large scale displacement of communities, often without financial compensation or alternative land made available on which to live.
- Pollution from uneaten feeds or waste products (e.g. faeces), cleaning fluids and antibiotics in the feeds, and excessive sedimentation from cleaning of ponds.
| What DLIST users say…”It is when the fish densities are increased beyond the ability of the local environment to assimilate their wastes that a problem occurs” |
- Introduction and escape into the wild of farmed alien fish species, or disease vectors such as viruses.
- Concentrated, unmoving fish populations also give parasites a permanent home and breeding ground.
- Aquaculturalists in Angola, Namibia and South Africa need to have water conserving strategies in place, so that they can protect their fish stock due to the water stressed environment they live in. Read more here.
- The issue of feeds in fish farming has been a controversial one. While vegetarian fish like tilapia require no meat products in their diets, carnivorous fish like salmon depend on fish feed of which a portion is usually derived from fish caught in the wild. In the case of carnivorous fish the input of wild caught fish exceeds the output of farmed fish by a considerable margin, since conversion efficiencies are not high. Attempts to replace fish meal and oil in fish feed with vegetable sources of protein like soybeans, barley, canola, corn, cottonseed and pea are underway but have yet to be proven successful. If plant based feeds are used in aquaculture, to be sustainable they must be sourced from agriculture that is sustainable. The wild (pelagic) fish may be containing contaminants and pollutants that accumulated in their bodies and, fed to the species in conventional aquaculture, may also contaminate or pollute our environment.
| What DLIST users say…. “ In fish farming up to five times the quantity of wild fish are used to produce pelleted fishmeal to feed farmed fish; putting huge pressures on already overfished resources”. |
- Unknown ecological impacts exist, especially if there is interbreeding between the farmed fish and the wild stocks, leading to hybridisation. This has recently been shown in a study to be a real, quantifiable problem with farmed salmon.
- Competition for resources and mates between escaped farmed and wild stocks reduce the vigour of wild stocks, particularly where they have been depleted by over-fishing.
Environmentally friendly methods
| What DLIST users say…” The types of aquaculture with minimal impacts are shellfish culture, harvesting of mussels, oysters, clams, etc in coastal or estuarine farms, as these mainly gain their food from filter feeding”. |
Land-based aquaculture operations offer total or partial isolation from the sea, which carries many advantages compared to farming in sea cages. As they provide control over the fish growing environment, there is a reduction of effluents containing high loads of fish waste products and chemicals used in the production that are released to the ocean. Complete isolation from the sea offered by these systems makes them ideal for farming with alien species and indigenous species that constitute a high disease and genetic risk to natural populations.
 An alternative to open ocean cage aquaculture in which the risk of environmental damage is substantially eliminated is practised through the use of a Recirculating Aquaculture System (RAS). This is a series of culture tanks and filters, where water is continuously recycled to prevent the deterioration of water quality. The water is treated mechanically through the removal of particulate matter, as well as biologically through the conversion of harmful accumulated chemicals into non-toxic ones.
| What DLIST users say…” Today you get marine predatory fish such as cobia being farmed on fish meal and fish oil free feed. Which is a remarkable achievement and bodes well for the future of aquaculture feeds which are moving towards a diet based primarily on vegetable proteins” |
\Organic Aquaculture is different from the conventional aquaculture because it is an overall system of farm management and food production that focuses on best environmental practices, a high level of biodiversity, preservation of natural resources and application of high animal welfare. Organic aquaculture is said to boast low production costs and higher quality yields.
| What DLIST users say…“ It should be borne in mind that the broiler and pig industries each consume substantially more fish meal than does aquaculture, and the protein conversions are less efficient than those achieved by fish” |
Organic aquaculture is punted as being feasible for small farmers, with a relatively easy to learn technology. It is said to be appropriate for rural areas. However, there is a need to educate people and draw more interest to learn the technology and to comply with internationally accepted standards for certified organic aquaculture production.
Other treatments such as UV sterilisation, ozonation, and oxygen injection are also utilised to maintain optimal water quality. Through this system, many of the environmental drawbacks of aquaculture are minimised including escaped fish, water usage and the introduction of harmful pollutants. These practices increase the efficiency of feed utilisation and growth by providing optimal water quality parameters.
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