Dietary carbohydrate and faecal waste in the Nile Tilapia (Oreochromis niloticus L.)

Public concerns about environmental pollution are putting increasing pressure on fish farms to treat their wastewater before release. The wastewater produced by the fish can also deteriorate water quality within the system. Aquaculture waste can be divided into solid waste and dissolved waste.Faeces ismain sources of solid waste. An increased consistency of faeces may improve its removal efficiency, thereby improving water quality. The removal efficiency of faeces by a collector (settling tank and/or Choubert) was proposed as an indicator for faeces consistency. Manipulation of the diet composition changed faeces consistency in tilapia. Soluble non-starch polysaccharide increased digesta viscosity and reduced faeces removal efficiency. Insoluble non-starch polysaccharide did not change faeces removal. Replacement of native starch by gelatinized starch improved faeces removal efficiency. Fermentation and viscosity of digesta are the main parameters affecting faeces consistency. An increased faeces removal, induced by dietary composition, lowered the organic matter load into the system, thereby increasing nitrification and dissolved oxygen. A detailed investigation on fermentability and viscosity of different ingredients can provide insight in characterization of faeces, thereby giving suggestion for diet formulation geared to maximize solid removal.