Hydrolysis lignin as a multifunctional additive in Atlantic salmon feed improves fish growth performance and pellet quality and shifts gut microbiome

The objective of this study was to evaluate hydrolysis lignin (H-lignin), derived from wood biomass, as a multifunctional component of aquafeeds. Atlantic salmon (28.8 +/- 1.1 g) were fed diets for 16 weeks, which included two H-lignin types (HL1 and HL2) at 15, 30 or 50 g/kg (wt/wt) or a control diet (no added H-lignin). HL1 was extracted with water such that no soluble sugar and oligosaccharides remain, while HL2 contains a higher fraction of water-soluble sugars and oligosaccharides. Pellet durability and density were measured. After 16 weeks, salmon were measured for weight and length, and whole carcass, hindgut and digesta contents were sampled. Pellet durability increased from the control to 30 g/kg H-lignin but decreased at 50 g/kg. Salmon fed diets with HL1 at 15 and 30 g/kg showed higher weight gain and lower feed conversion ratio compared with salmon fed the control diet and 50 g/kg HL1. There were no significant differences in whole-body composition or intestinal morphology. Microbial characterization (16S) revealed lower abundance of Proteobacteria, higher abundance of Mycoplasmataceae and increasing Lactobacillaceae abundance with higher HL1 inclusion. This study demonstrates that HL1 (at 15 and 30 g/kg) shows potential as a functional feed additive for salmon.