Abstract

A digestibility trial was developed with the aim of evaluating the effect of solid-state fermentation with Aspergillus niger on the nutrients apparent digestibility of rapeseed cake (Brassica napus) when fed to rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar). Apparent digestibility of dry matter, protein, lipids, carbohydrates, energy, phosphorus and fibre were evaluated using the substitution approach (70% of reference diet + 30% of test ingredient) and chromic oxide as inert marker. Faeces were collected using a settlement column. The results indicate that solid-state (SSF) of rapeseed cake with Aspergillus niger increase apparent digestibility coefficients (ADC) of dry matter (29.6% and 10.4%), protein (7.1% and 1.8%), phosphorus (413% and 446.9%) and fibre (222.6% and 200.4%), for rainbow trout and Atlantic salmon respectively. However, ADC of lipids and carbohydrates were reduced for both species in fermented rapeseed cake. After the fermentation, the digestibility of energy had an increase of (4.3%) for the trout, but for the salmon, it was reduced by (17.7%). In conclusion, this study shows the potential of solid-state fermentation with Aspergillus niger as a feasible bioprocess to improve the nutritional value of agro-industrial by-products such as rapeseed cake for aquafeeds.