Wheat grains fermented by fungal mycelia (Pleurotus ostreatus or Lentinus edodes) as alternative feed ingredients for juvenile rainbow trout (Oncorhynchus mykiss)

Abstract

We investigated the effects of replacing non-fermented wheat grains with wheat grains fermented by fungal mycelia in the diet of juvenile rainbow trout (Oncorhynchus mykiss). We assessed growth performance, feeding parameters, and body composition in three experimental groups (0.33 ± 0.01 g, in triplicates of 50 individuals each). The diets for all the groups contained ca. 43% protein and 19% lipids. Experimental diets were made by replacing the 100 g kg−1 of wheat grains present in the basal diet (CTRL) with the same proportion of wheat grains fermented by Pleurotus ostreatus (PWD) or Lentinus edodes (LWD) mycelium. Fish were fed to apparent satiation twice a day for 56 days. Both, PWD and LWD, significantly increased fish body weight from day 28 onwards. Final body weight was 2.37 ± 0.04 g (CTRL), 4.29 ± 0.02 g (PWD), and 3.50 ± 0.05 g (LWD), and feeding efficiency (%) was increased from 64.5 ± 0.7 (CTRL) to 92.5 ± 0.5 (PWD) and 84.8 ± 1.5 (LWD). The experimental diets also improved nutrient retention efficiency (%): 30.0 ± 0.5 (PWD), 27.7 ± 1.1 (LWD), and 21.0 ± 0.1 (CTRL), for crude protein; 40.3 ± 0.6 (PWD), 31.0 ± 1.8 (LWD), and 16.1 ± 0.7 (CTRL), for ether extract; and 16.1 ± 0.1 (PWD), 14.0 ± 0.3 (LWD), and 11.6 ± 0.6 (CTRL), for phosphorus. Body lipid content was highest for PWD followed by LWD and CTRL (81.4 ± 1.4, 63.2 ± 2.5, 42.3 ± 2.6 g kg−1, respectively), while viscerosomatic index was lowest for PWD (p < 0.05). Liver glycogen in LWD and PWD fish (0.62 ± 0.10 and 0.21 ± 0.08% liver weight) was significantly higher than in CTRL fish (0.05 ± 0.01% liver weight). Wheat-mycelium meals appear to be suitable dietary ingredients for improving juvenile rainbow trout growth and nutritional performance. These benefits vary according to the mushroom species used.