Reduction of Waste Output from Salmonid Aquaculture through Feeds and Feeding

Abstract

The main goal of aquaculture is to efficiently convert feed into fish and shellfish. Inherent to this practice is the generation of waste; however, from a waste management viewpoint, aquaculture differs in important respects from terrestrial animal farming. Measurement of actual feed intake is nearly impossible; consequently, unconsumed feed contributes a relatively large proportion of total waste output in most operations. Moreover, containment of wastes is difficult, and wastes are rapidly dispersed into the surrounding waters. Monitoring and estimating quantitative waste outputs in effluent directly is an inaccurate and costly process. Other methods of estimating the waste output from aquaculture operations should be used. Because most aquaculture wastes are dietary in origin, efforts to reduce waste should focus on nutrition and feeding, including the formulation of special diets, development of feeding systems, and improvement of the efficiency of nutrient utilization. Modern low-pollution or highly digestible, nutrient-dense (HND) diet formulations yield outputs of less than 150 kg solid waste and 3 kg phosphorus per metric ton of salmonid fish produced. However, in addition to the use of HND diets, reduction of wastes in salmonid culture requires revised feeding standards based on average digestible energy requirement per kilogram of fish produced and a target feed efficiency (gain: feed) of much greater than 1.0. Experimental data with HND diets, feeding standards based on energy requirements, and biological procedures for quantifying waste output in the effluent are reviewed.