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

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.

Automated summary

The study tested the effect of using yeast and spent grain as partial replacements for fishmeal in fish diets, showing that they can be a good source of protein with good digestibility for rainbow trout and gilthead sea bream.