The physico-chemical properties of nutrients in£uence the physical characteristics of faeces and thus may a¡ect waste removal e⁄ciency. The aim of this study is to assess the e¡ect of type of non-starch polysaccharide (NSP) on digesta viscosity, faeces recovery and nutrient digestibility in Nile tilapia. Insoluble (cellulose) and soluble (guar gum) NSPs were included separately and combined at a level of 8%, thereby formulating four experimental diets. The diets were assigned to 16 tanks with 35 ¢sh each, with four replicates for each diet. Cellulose inclusion did not in£uence digesta viscosity, growth and digestibility of protein and starch and tended to increase faeces recovery (P 5 0.06). Guar gum inclusion increased digesta viscosity and reduced the growth and digestibility of protein, fat and starch (Po0.01). Faeces recovery was reduced by 42% in diets containing guar gum. There were interaction e¡ects (Po0.05) between cellulose and guar gum for the growth and feed conversion ratio, indicating that cellulose alleviated the negative impact of guar gum. In conclusion, dietary soluble NSPs increase organic matter load in the culture system through a reduction in faeces recovery and nutrient digestibility, whereas insoluble NSPs improve the removal e⁄ciency of particles by increasing faeces recovery.
The discharge of waste from aquaculture operations can lead to eutrophication and destruction of natural ecosystem in receiving water body. A controlled waste production strategy is necessary to maintain sustainable aquaculture growth into the future. As feed is the major source of waste in aquaculture, the management of aquaculture waste should be approached through diet formulation or feeding strategies. Highly digestible diets have been introduced as a solution to reduce solid waste excretion. Further reductions in solid waste can be achieved through careful selection of feed ingredients and feed processing to improve nutrient availability. An increase in faeces consistency by diet manipulation can improve solid removal efficiency. This condition can reduce the proportion of solids in discharged water in the effluent and also improve farm water quality. A reduction in dissolved nitrogen waste can be achieved by ensuring a balance between protein and energy causing fish to use non‐protein sources as energy. Phosphorous waste can be decreased through careful ingredient selection and proper processing to improve digestibility. A proper feed ration and feeding method for each species should be adopted because feed waste constitutes a large part of waste production.
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