The growing demand for nutraceuticals has driven interest in upcycling low-value proteins from processed animal by-products and insect larvae into functional protein hydrolysates. This study evaluated five such hydrolysates in comparison to a high-value commercial reference (CPSP90), assessing the proximate composition, amino acid profile, molecular weight distribution, antioxidant activity, and bacterial growth dynamics. Results revealed a wide variability in the composition and bioactivity, driven by the raw material and processing conditions. All hydrolysates displayed a medium to high crude protein content (55.1–89.5% DM), with SHARK being the most protein-rich. SHARK and SWINE hydrolysates were particularly rich in collagenic amino acids, while FISH and CPSP90 contained higher levels of essential amino acids. FISH and INSECT demonstrated the strongest antioxidant activity, with INSECT also showing the highest protein solubility. INSECT and SWINE further displayed mild, selective antibacterial effects, indicating a potential for disease mitigation. Conversely, SHARK and FISH supported opportunistic bacteria growth, suggesting a potential use as nitrogen sources in microbial media. These findings highlight the nutritional and functional versatility of animal-derived protein hydrolysates and support their integration into sustainable feed strategies within a circular bioeconomy.

Upcycling meat and fish by‐products into bioactive protein hydrolysates promotes zero‐waste practices within the circular bioeconomy and provides locally‐sourced alternatives to replace fishmeal (FM) in aquafeeds. In this study, novel hydrolysates were developed from blue shark skin, fish by‐products, and swine processed animal protein, aiming to reduce the high‐quality FM inclusion in European seabass ( Dicentrarchus labrax ) diets. Four isoproteic (53%) and isolipidic (18%) plant‐based diets were formulated: a control (CTRL) diet containing 12.5% FM was compared to three experimental diets, including 3% of each hydrolysate at the expense of FM‐protein: SHARK, FISH, and SWINE. Seabass juveniles (13 g) stocked in 160 L tanks (3.9 kg/m ³ ) were fed the diets in triplicate, three times daily until satiety, for 89 days. All diets were equally well accepted, promoting similar feed intake, daily growth index (1.6), and efficient feed conversion ratio (1.0–1.1). All fish at least quadrupled their initial size, but those fed the SWINE diet showed the highest body weight (55 g) and significantly higher condition factor (1.22), hepatosomatic index (HSI) (1.6), and viscerosomatic index (VSI) (8.4). Intestinal integrity remained similar across treatments, and apparent digestibility coefficients (ADCs) of protein and fat were above 96%. Iron (Fe) ADC was at least doubled with hydrolysates inclusion. Whole‐body and muscle composition were similar across groups. However, the muscle metabolome of the SHARK‐fed fish exhibited higher levels of glycolytic intermediates and lower levels of glucogenic amino acids (AAs) and fumarate, suggesting an increased catabolic activity. However, these changes were not reflected in fish growth performance or muscle flesh quality, which remained similar among treatments.

Reducing dependence on marine-derived ingredients like fishmeal, while maintaining the robustness of carnivorous species, like European seabass (Dicentrarchus labrax), remains a challenge for sustainable aquaculture. Photobacterium damselae subsp. piscicida (Phdp) outbreaks are still responsible for significant economic losses, but functional ingredients capable of modulating immune responses may enhance resilience to a Phdp challenge. In this study, fish were fed four balanced diets for 89 days: a plant-based control (CTRL) and three diets including three protein hydrolysates (SHARK, FISH and SWINE) at the expense of fishmeal protein. After the feeding trial, fish were intraperitoneally injected with Phdp and sampled at 0, 4, and 24 h post-infection for hepatic oxidative stress, plasma biochemical profile and gene expression related to intestinal integrity and immune response. All diets were well accepted and no differences in survival could be detected. Hydrolysate inclusion induced distinct baseline physiological states, likely shaping subsequent responses to infection. SWINE and SHARK diets increased hepatic glutathione reductase activity, while SHARK-fed fish consistently showed lower lipid peroxidation (LPO). In contrast, FISH-fed fish exhibited a higher LPO and lower circulating proteins. Upon infection, a metabolic reorganization was triggered across all groups, including a reduction of plasma glucose except for SHARK. In this group, stable glycemia occurred alongside reduced expression of intestinal tight junction markers, suggesting a potential trade-off between energy homeostasis and barrier integrity. Overall, replacing fishmeal protein with animal-derived hydrolysates in high plant-based diets modulated host responses through primarily metabolic and redox pathways, without clear improvements in resistance to Phdp challenge.