Filamentous fungus Paecilomyces variotii in feed for Rainbow trout (Oncorhynchus mykiss) : assessment of apparent digestibility and early signs of inflammation
Abstract: Aquaculture production has been increasing rapidly over the last few decades and therefore the amount of feed needed for the increasing production is also on the rise. Salmonids and other farmed carnivorous fish require high amount of protein in their diets, which is currently supplied mostly by fish meal or soy bean. Therefore, there is a need to identify other alternative sustainable protein sources, preferably those that are not grown on arable land or can be used directly for human consumption. Single cell protein are microorganisms such as fungi, bacteria, yeast and mould, that contain a high level of protein and can be grown on various substrates such as resi-dues from other industries. Filamentous fungus Paecilomyces variotii is a mould that can be grown on residues from the wood industry and is characterized by a high pro-tein content. The objective of this thesis is to assess the potential of using P. variotii as protein source in diets for rainbow trout (Onchorhyncus mykiss) through assessment of ap-parent digestibility. In addition, intestinal samples were taken for histological analysis of early signs of intestinal inflammation. P. variotii has been included in diets to rainbow trout at 20% and 30% inclusion levels. Results show that the inclusion of P. variotii at all levels lowered the apparent digestibility coefficient of the diet dry matter, gross energy and crude protein. However, apparent digestibility of the test ingredient was higher for dry matter, energy and crude protein when the test ingredient was exposed to double extrusion during the feed production. Signs of inflamed intes-tines were least present in fish fed diet with 20% inclusion of test ingredient which may indicate a positive effect of P. variotii in the gut at lower inclusion levels.
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