3.2. Quantifying of waste production
Waste production in aquaculture systems is quantified either by the nutritional approach through determining the apparent feed digestibility of fish or is directly analyzed by quantification of excretion products in the culture water (Cho et al., 1991). Calculated values are often derived from feed trials under well-controlled experimental conditions and not always reflect the feed digestibility of the fish under more realistic culture conditions. In addition, due to partial breakdown of the waste to gaseous forms within the culture system, not all of the generated fish waste is discharged with the effluent water. Despite these shortcomings, the nutritional
approach is often preferred over the alternative method in which waste is directly quantified in the culture system. Quantification of waste production by means of this latter method, even in the simplest of experimental systems, is complicated due to the difficulty in fitting a sampling regime to accurately estimate the fluctuating waste production by fish. Furthermore, factors such as the cleaning regime of the culture system, the frequency and duration of water
replacement in the culture systems as well as analytical errors in quantifying the waste products (e.g. sample preservation, analytical inaccuracies) contribute to the inaccuracy of the latter method (Roque d’Orbcastel et al., 2008).