Combining Fish and Crustacean Byproducts as Primary Ingredients in Pelleted Aquafeed: The Effect of Byproduct Type on Pellet Physical Properties

Over the past three decades, global aquaculture production has significantly increased, emphasizing the need for sustainable and cost-effective alternatives to traditional fish meal in aquafeed. This study’s objective was to elucidate the impact of utilizing a combination of fish and crustacean byproducts—namely, smoked salmon (Salmo salar) skins (SSs), smoked salmon trimmings (STs), and shrimp (Litopenaeus setiferus) heads (SHs)—as primary ingredients in pelleted aquafeed. Importantly, this work focuses on nonextruded pellets, where the physical properties are more influenced by ingredient composition compared to extruded pellets. The tested formulations were not nutritionally comprehensive for any specific commercial aquaculture species, as the goal of this study was to highlight the effect of the byproducts on pellet physical integrity. SH and de-oiled solid fractions of SS and ST were dehydrated for 24 h at 60°C, ground into dried powders, and formulated into six samples at a 1:1 (w/w) ratio and one sample at a 1:1:1 ratio. Potato starch (80 g/kg) was added to each sample, along with varying deionized (DI) water amounts before steam conditioning, pelletizing, and drying. Analyses included pellet nutrient composition, floatability, durability, water stability, bulk density, water absorption index (WAI), and water solubility index (WSI). Results revealed that SS pellets exhibited 97% floatability at 1 min, decreasing to 70% at 60 min. SS and ST combinations showed slow sinking behavior, while all other formulations sank quickly. Pellets containing SH had lower water stability (65.65% ± 4.44% to 0.05% ± 0.07%), in contrast to over 92% for SS and ST pellets. Durability ranged from 98.48% ± 0.37% for SS to 75.29% ± 5.82% for SH and ST combinations, further underlining the significant impact of byproduct choice on pellet performance. Overall, the inclusion of SS or ST and their combination as primary ingredients for pelleted aquafeed produced pellets that scored well on important quality parameters, while pellets containing SH performed poorly. This information may be used in the development of nutritionally comprehensive nonextruded aquafeeds containing SS and/or ST to conduct feeding trials with commercially relevant species.