Increasing production volumes of fed aquaculture have caused an escalating demand for alternative protein raw materials in fish feed. Agro-industrial by-products such as sunflower meal are relatively abundant and cheap, but inclusion levels are limited due to the presence of antinutritional factors, an imbalanced amino acid profile and fiber. Solid state fermentation is a processing method which intends to reduce the content of fiber and antinutritional factors, increase protein content and nutrient digestibility to make plant raw materials more suitable in aquafeeds. The aim of this study was to evaluate the effect of fermented sunflower (FSF) meal in diets for Atlantic salmon farmed under field conditions at two commercial-like fish farms in a coastal and fjord location with 309 500 and 235 800 fish, respectively.
Atlantic salmon were fed diets containing 5% and 10% FSF meal and a reference diet containing 5% non-fermented sunflower (SF) meal (Table 1). The field experiment lasted for eight and eleven months at the coast and fjord location, respectively. The technical quality of the pellets was assessed based on expansion, hardness, durability and sinking velocity. Digesta samples were collected from the distal intestine (DI) for microbiota analysis with 16s ribosomal rRNA sequencing, and DI tissue was used for RNA sequencing and histological analysis with H&E, periodic acid-Schiff and Alcian blue staining.
All diets showed high physical pellet quality. There were no significant differences between dietary groups related to feed intake, feed conversion ratio or growth rate. Histological analyses revealed that fish at the coast location had significantly less ectopic goblet cells in the DI, when fed 10% FSF meal. At the fjord location, fish fed 10% FSF meal had a significantly reduced prevalence of prominent DI inflammation (Figure 1). 16s RNAseq of DI digesta showed that Lactiplantibacillus (p = 0.0001) and Lactobacillaceae (p = 0.006) were significantly more abundant in fish fed 10 % FSF meal, and beta diversity increased significantly (Figure 2).
The results of this study indicate that FSF meal promotes gut lactic acid bacteria and improves gut health in Atlantic salmon farmed under commercial-like conditions.