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Factors affecting the quantity and quality of faecal waste in striped catfish

Trần Lê Cẩm Tú, Tu

Samenvatting

This study investigated the nutritional interventions to alter/improve faecal pellet quality (which could lead to better and more complete removal of faecal waste) and the enhancement of the stability of egested faeces. In this thesis, striped catfish was taken as a model species, to study the options for aquaculture waste management. Up till now, it is not clear if nutritional interventions targeted to reduce the amount of faecal waste can go along with improving the faecal quality. The main aim of this research was to study the impact of different nutrition interventions on both the quantity and quality of faecal waste produced by striped catfish (Pangasianodon hypophthalmus, Sauvage, 1878). The most ideal nutritional interventions would be those that reduce the quantity and at the same time, improve the quality of faeces. To reach the aim, we conducted four studies. Firstly, we determined the characteristics of waste production and digestibility of dietary ingredients. Fifteen commonly applied ingredients in feed formulation of striped catfish were studied: protein-rich ingredients, ingredients relatively rich in non-starch polysaccharides, and oil and starch-rich ingredients. Secondly, we tested the impacts of the ingredients’ particle size and the dietary viscosity on digestion, performance and faecal waste management of this fish. Thirdly, we analysed the dose-response relationship between dietary viscosity and nutrient digestibility and faecal waste characteristics in striped catfish and the long-term impacts of viscosity on the performance of striped catfish. Lastly, we assessed the relationship between the physical and chemical characteristics of chyme and apparent faecal nutrient digestibility. In particular, this study determined the effect of dietary viscosity on chyme characteristics in different segments of the gastrointestinal tract (GIT) of striped catfish, and the progression of nutrient digestion throughout the GIT. In all our studies we have noticed that the ingredient composition of a feed strongly determines the amount of faecal waste produced on a diet. Faecal quantity can be altered by feed technology/feed processing conditions (e.g., grinding screen size). For striped catfish, feed and faecal pellet binders, which increase the dietary viscosity, should not be used in the diet because it reduces the dry matter digestibility even at very low inclusion levels. The negative impact of dietary viscosity on digestion in striped catfish appears very proximal in the gastrointestinal tract (stomach). This negative impact on digestion is not compensated after the evacuation of the chyme from the stomach. The stability of faecal waste is determined by the ingredient composition of the feed consumed by the fish.