Apparent digestibility coefficients of brewer's by-products used in feeds for rainbow trout (Oncorhynchus mykiss) and gilthead seabream (Sparus aurata)

Abstract

A trial was conducted to test the effect of partial replacement of fishmeal by two brewery industry byproducts, yeast and spent grain, included in isoproteic (41\% CP) and isolipidic (22\% CL) diets for gilthead sea bream (Sparus aurata) and rainbow trout (Oncorhyncus mykiss), having in mind the availability of these byproducts. A first step before an ingredient is included in a commercial feed is to evaluate the nutritional quality of these raw materials by measuring their digestibility. Thus, the apparent digestibility coefficients of the diets and ingredients were determined after a 30 days feeding trial and faecal collection. Apparent digestibility coefficients of these by products in the case of rainbow trout varied between 75 and 88\% whereas for gilthead seabream was between 71 and 88\%. According to the results obtained, the inclusion of 20-30\% of brewers' spent yeast and spent grain in the feed for carnivorous fish either from fresh (rainbow trout) or marine (gilthead seabream) gave similar results to a feed with fish meal as the main protein source and show a good protein, lipid and amino acid digestibility. Taking into account that these by-products are produced in large quantities in Europe, they can be a potential source of protein to reduce the use of plant proteins or fish/animal byproducts (trimmings) and increase the sustainability of both sectors, brewery industry and aquaculture.