High-solid loading alkaline autoclaved-processed Codium tomentosum as a sustainable feed ingredient for juvenile european seabass (Dicentrarchus labrax)

Abstract Codium tomentosum , a marine green macroalga is also produced in integrated multi-trophic aquaculture (IMTA) systems; however, its use in aquafeeds remains unexplored. This study evaluated the potential of C. tomentosum as a feedstuff for European seabass ( Dicentrarchus labrax ) and, for the first time, applied a high-solid-loading alkaline autoclave pre-treatment to enhance its nutritional value. Macroalgal biomass was treated with 1N NaOH (75% moisture) at 121 °C for 30 or 60 min, producing a slurry hydrolysate that was dried and incorporated at 7.5% into experimental diets. Four diets were tested in triplicate: a control diet, with no incorporation of C. tomentosum , a diet with untreated C. tomentosum (COD), and two diets including pre-treated C. tomentosum for 30 min (COD30) or 60 min (COD60). Two trials were performed: a digestibility trial (initial bodt weight (IBW) = 63 g) and an 11-week feeding trial with European seabass (IBW = 38 g) fed to apparent satiation. Inclusion of untreated C. tomentosum increased apparent digestibility but did not affect growth performance or feed efficiency. In contrast, fish fed the COD30 diet showed higher protein and amino acid digestibility and improved growth performance, feed utilization, and protein efficiency ratio compared with both control and untreated C. tomentosum diets. Extending the pre-treatment to 60 min did not lead to additional benefits and tended to reduce digestibility, feed intake, and growth. Whole-body composition and plasma biochemical parameters did not differ among treatments. Overall, a 30-min high solid-loading alkaline autoclave pre-treatment of C. tomentosum enhanced nutrient digestibility, growth, and feed utilization, supporting its potential as a sustainable ingredient in aquafeeds.