Dietary supplementation of hydroxyproline: Beneficial to the growth performance and muscle quality of spotted seabass (Lateolabrax maculatus)

Hydroxyproline (Hyp), a critical component of collagen, has demonstrated potential in enhancing muscle quality in aquaculture species, yet its effects on spotted seabass ( Lateolabrax maculatus ) remain unexplored. This study investigated the impacts of dietary Hyp supplementation (0–0.8 %) on growth performance, muscle quality, and molecular pathways in spotted seabass to identify optimal inclusion levels and underlying mechanisms. A 60-day trial evaluated five isonitrogenous diets (0 %, 0.2 %, 0.4 %, 0.6 %, and 0.8 % Hyp) in 300 juvenile seabass (64.91 ± 2.24 g). Growth metrics, muscle texture, water-holding capacity, hydroxyproline content, prolyl-4-hydroxylase (P4H) activity, gene expression (e.g., myod1 , mef2 ), and AKT/mTOR signaling were analyzed. Hyp at 0.4–0.6 % (H4–H6) enhanced final body weight (6.7 %), specific growth rate (10.9 %), and reduced feed conversion ratio ( P < 0.05). The H6 group exhibited superior muscle hardness, chewiness, and reduced cooking/freezing loss, correlating with elevated P4H activity and Hyp content. Muscle development genes ( myod1 , titin ) peaked at 0.6 % Hyp, while AKT/4E-BP1 phosphorylation indicated activated protein synthesis. Excessive Hyp (0.8 %) induced oxidative stress, reversing benefits. Moderate Hyp supplementation (0.6 %) optimizes growth and muscle quality in spotted seabass by enhancing collagen synthesis and AKT/mTOR signaling, whereas over-supplementation impairs outcomes. These findings advocate targeted Hyp inclusion in aquaculture diets to improve productivity and fillet quality. • Optimal Hydroxyproline (Hyp) supplementation (0.6 %) enhances growth performance in spotted seabass by improving weight gain, feed efficiency, and muscle protein content. • Improved muscle quality with Hyp supplementation, including enhanced hardness, elasticity, cohesiveness, and reduced cooking/freeze-thaw losses, is achieved through collagen synthesis and structural remodeling. • Molecular mechanisms involve upregulation of muscle development genes ( myod1 , mef2 , titin , neb ) and activation of protein synthesis pathways (AKT/mTOR signaling), supporting muscle texture optimization. • Excessive Hyp (>0.8 %) may impair muscle quality and antioxidant defenses, highlighting the importance of dosage control. • First evidence in spotted seabass demonstrates Hyp's dual role in promoting growth and enhancing product quality, offering practical value for sustainable aquaculture practices.