Approccio zootecnico alla stima delle emissioni eutrofizzanti dell'allevamento ittico intensivo e strategie per il loro contenimento

Although the contribution of aquaculture operations to water eutrophication is generally minor in the contest of the industrial, domestic or agricultural pollution, nevertheless the potential adverse effects and risks of environmental impact of nutrients generated through the incomplete utilisation of feeds by intensively cultured fish have been powerfully argued by environmental scientists and are of great public concern, making waste loading control a crucial point for sustainability in certain inland and coastal locations heavy exploited by intensive fish farming. A sound approach to this issue claims first for reliable estimates of the actual nutrient output from fish farms to be obtained, being this assessment not always easy to be set through the chemical-limnological methods of water quality monitoring and analysis currently adopted by most public agencies responsible for the regulation of wastes discharged by fish farms. On the other hand, the growing awareness of farmers on this issue as well as the EU and national rules rely on the adoption of all measures enabling prevention and minimisation of nutrient release "at the source" by improving the conversion efficiency of aqua-feeds while optimising feeding practices and techniques. In this direction, the last decade marked out a constant and substantial reduction of nutrients wasted to the environment per unit of fish biomass produced. This was mostly a result of the concurrent and responsible measures and actions set up by the feed-mill industry and fish farmers which were able to translate into practice the great deal of new knowledge gathered from the research in the fields of fish feeding-nutrition, feed formulation-processing and farming techniques-technologies. With reference to the most important fish species cultured in Italy, the present paper describes the layout, current perspectives and constraints of a biological-nutritional method when applied for predicting the waste load generated by intensive fish farming. A further aim of this work is to present a brief review of the main nutritional and feeding strategies which had already been set up or are going to be implemented for further reducing at the source the excretory and feed wastes originating from fish farms. However, it does not consider the fundamental and effective role of possible bio-technological treatments to be applied to the effluents that, in addition to a continuous fine-tuning of the nutritional and feeding strategies, could lead to a substantial shortage of nutrients being actually lost to the environment from land-based intensive aquaculture systems.