Poo Matters: Determinants of Faecal Quality in Salmonids

Fish culture, like all animal production systems, generates waste. Waste produced in a fish culture system can be classified into solid and dissolved waste. The major source of solid waste is undigested feed, excreted as faeces. Removal success of faeces from production system depends on characteristics like size, stability and density of faecal pellets. This thesis investigated the factors determining faecal quality in salmonids. First, tools were developed to determine stability, density and structural features of fish faeces. It was observed that closely related fish species produce faeces with different sizes and stability, even when fed the same diet and reared under the same conditions (same systems). Further, it was observed that dietary factors like ingredient and nutrient composition play an important role in determining faecal quality. Finally I showed that rainbow trout produce faeces of diverse types and that faecal pellets have a dual mucoidal coating.