Noun:
	the complex of living organisms, their physical environment, and all their interrelationships in a particular unit of space.

The impact of fish farming

In intensive fish farming, it is the nutrients in the feed and their combination, both physically and chemically in fish growth, which brings about the creation of food for human consumption. From ecological and animal feed/human food results perspectives, it is essential that feed manufacturers develop the highest order of nutritional expertise and production technology.

The primary role must be to maximise the nutrient retention and growth rate of the stock and minimise the feed resource wastage and nutrients entering the environment.

This is the aspiration of the whole aquaculture industry and indeed all those involved in food culture, both on the land and in the sea.

Environmental impact or nutritional benefit?

Until recently, the world’s oceans have been regarded as an inexhaustible well, which can be harvested without the need to return anything.  This attitude defies the long-established principle of traditional farming where, if fields are not fertilised to replace the nutrients removed by growing crops,the following season’s crop growth and harvest will fail. 

In order to maintain primary production and preserve the ecological balance of marine ecosystems, the amount of nutrients removed must be balanced by an equivalent return of nutrients.  In the case of fish farming, most of the ingredients in fish feed are of marine origin and should, therefore be returned to the sea, to be recycled in the marine ecosystems.

The ocean has also been regarded as a vast sink that can receive huge quantities of nutrients (and all kinds of other waste) without ill effect.  In general it is true that, in open marine systems, dissolved nutrients are easily diluted and carried away in the currents.  However, heavy insoluble particles, whatever the source, may sediment on the seabed and cause localised impact if released in sufficient quantity.  In the case of fish farming, feeds of optimal composition, together with appropriate on-farm feeding regimes, minimise this effect by maximising protein retention in fish flesh and, thereby, minimising waste.  This applies equally to open cage culture systems and to land-based tank and plant systems.

The aquaculture industry is particularly aware of the importance of feed composition, as well as feed and stock management, in installations that use rivers, lakes and closed sea basins.  In such situations, nutrients and organic matter from any industrial source can contribute considerably to the total nutrient flux and oxygen demand.  All industries share the responsibility to minimise such effects.

extract from “Aquaculture and the Environment; New Perspectives” -   AKVAFORSK(Norway) and Biomar AS

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