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The main criteria for the development of low impact diets.
 Four main factors contribute to the efficient utilisation of the nutrients in fish feed and to low nutrient losses to the environment. Biomar has led the way in the development of diets with these characteristics and continues to invest heavily in an active research and technical development programme.
1. The feed must be balanced according to the nutrients and metabolic requirements of the fish.
2. The nutrients in the feed must be as digestible is possible so that they can be fully utilised by the fish.
3. Feed loss and the resultant nutrient leaching from the feed must be avoided.
4. The feed intake must be higher so that the fish grow at or close to the maximum growth rate. This minimises culture time and thereby reduces costs to production and the effects on the environment of ongoing maintenance metabolism in the stocks.
The feed constituents with impact potential.
There are many sources of waste that have the potential to affect the environment in some way. In reality, fish farming, the focus of this document, is a minor contributor (relative, for example, to agricultural and domestic sources) but has to be environmentally responsible. The examples that are given for aquaculture also apply to all other sources of waste that contain the constituents described. Full awareness of impact potential enables the minimisation of effects.
The constituents of fish diets that have the potential to impact on the environment are the following:
The impact of these constituents on the ecosystem can come from
1. waste food,
2. undigested/indigestible food,
3. excretory products entering the aquatic environment,
hence the importance of points 1 to 3 above.
Protein is the most important contributor to the growth of any animal organism, via the metabolic processes involved in the formation of flesh. Protein can also act as an energy source, via the metabolic process of the deamination. However, in both environmental and feed resource terms, it is undesirable for protein to be used for anything other than growth. 
This is because the deamination process removes the valuable growth potential of protein by causing the breakdown of its constituent minor acids. This leads in turn to the excretion of soluble N, mainly as ammonia, the main excretory product in fish metabolism. Soluble N can be limiting to primary plant production, (through algal blooming) and may change the balance between the algal species in enclosed seawater locations, where the lack of tidal flushing can lead to a build-up of soluble N in the course of time. In open marine conditions, seasonal oceanic upwelling tends to be the dominant source of soluble N and localised concentrations are quickly dispersed by tidal and wind generated currents.
Biomar has led the way in the formulation of rations in which fats are the dominant energy source. Not only does this help to "preserve" protein for growth, but also it is more efficient energetically than protein deamination as a source of energy. The breakdown products of fat metabolism also have the advantage of being environmentally benign (water and carbonates).
Among the minerals, phosphorus (P) is the most important in relation to environmental effects, particularly in fresh and brackish waters. Fish obtain their phosphorus requirement almost entirely from their diet whilst many of their other mineral needs are obtained, either partially or totally, by absorption from the water in which they swim. Phosphorus is the nutrient that is most commonly limiting to primary plant production in fresh water, and is a factor in algal blooms. In modern fish rations, ash levels are controlled by ingredients choice so that, as far as possible, the phosphate content of the ration is matched to the dietary needs of the fish, thereby reducing the risk of impact to a minimum.
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