Fish nutrition: Improving nutrient efficiency and water use

Be it a semi-intensive or a totally intensive culture system, aquatic animal production depends on the availability of essential nutrients and energy supplied in the form of supplementary / complementary or complete feeds. Under any of these circumstances, the cost of these nutrient inputs remains high. Adequate nutrition is essential for the maintenance of vital functions with significant impacts on early development, growth, health, flesh quality and reproductive performance. Over the past decades, nutrition research has greatly contributed towards the remarkable development of feed-based intensive aquaculture around the world, in optimising feed quality and in the reduction of feed cost in the overall production. It is also now fully demonstrated that optimisation of the nutritional quality of the feeds and the feeding strategies can considerably improve the efficiency of fish production, environmental quality and the nutritional value of farmed fish. While knowledge of the nutritional requirements for a given production and for each of the species involved is indispensable, the supply of such nutrients in an available form will naturally vary depending upon the culture systems. Since pond culture remains by far the predominant form of aquaculture in Eastern Europe, integrated knowledge of the functioning of the pond ecosystem with precise quantification of the natural nutrient flow remains a big challenge for the fish nutritionist and the fish farmer. Development of the aquaculture is closely linked to the availability of resources: water, land, nutrient sources supplied as feeds or fertilisers. Although much progress has been made in selected sectors, there is much room for improvement of efficiency of aquaculture. Analysing the flow dynamics of major elements using reliable methods and models should facilitate our understanding how nutrients are converted into edible products of interest to the human food basket. Elemental stoichiometry is one such integrated approach not only for analysing nutrient fluxes in individual fish but also to gain quantitative knowledge on nutrient dynamics in aquaculture production systems. Given the global demand for water, reducing water use for aquatic animal production is a real challenge which needs to be addressed. This concerns both on-farm water use and feed-resources associated water use. Whether different aquatic production systems are equally “water-efficient” is another debated issue. We have very little information also as regards the virtual water-content of farmed fish and shrimp, due both to technical and conceptual reasons. Under intensive aquaculture conditions, much progress has been made to reduce our reliance on fishery-derived ingredients such as fishmeal and fish oil as protein and fat sources in feeds for fish. Inclusion of alternative protein and fat sources should also take into account the overall impacts in terms of resource and water use. Increasing efficiency in nutrient conversion and water-use are two major issues which need to be addressed to ensure aquaculture as the major supplier of animal protein to humans in the coming decades.