Shrimp hydrolysate-based palatability enhancer: A strategy to reduce fish-in fish-out ratio in marine fish species

Reducing aquaculture’s reliance on wild fish remains a major challenge. Protein hydrolysates, often derived from food by-products, offer a promising, sustainable, and functional alternative to marine proteins. This study evaluated their use as a palatability enhancer (PE) by top-coating feeds with a low-dose liquid hydrolysate, primarily from shrimp, to reduce fish meal (FM) in juvenile red seabream ( Pagrus major ) diets. Experimental feeds included a high FM diet (HFM, 30 % FM), a low FM diet (LFM, 15 % FM) and two additional diets with 2 % PE top-coated (HFM+PE and LFM+PE). Six replicate tanks, each with 40 fish, were fed one of the diets twice daily to satiety for 15 weeks. Half the tanks experienced intermittent stress (1-min net chasing for one week, every 3 weeks). After the trial, fish were challenged with Edwardsiella tarda . Both basal diets resulted in comparable growth and feed efficiency. Reducing fish meal from 30 % to 15 % in the LFM diet resulted in a baseline reduction of approximately 25 % in wild fish use, as estimated by the economic Fish-In: Fish-Out (eFIFO) ratio. PE supplementation further improved growth (+5.6 % for SGR), health, and feed utilization (-7.5 % for FCR), enabling an additional 6 % reduction in wild-caught fish input compared to the LFM diet alone. The beneficial effects of PE were consistent despite intermittent stress, and survival following bacterial challenge was significantly higher with PE supplementation. In conclusion, liquid hydrolysate used as a PE provides a cost-effective way to reduce pressure on wild fish stocks while maintaining high feed performance. • Liquid shrimp hydrolysate top-coated on low fish meal diet as palatability enhancer. • Hydrolysate increased feed intake and growth by ∼6 % under repeated stress. • Hydrolysate mitigated negative effects of low fish meal diets on performance. • Hydrolysate maintained fish health and resistance to disease. • Hydrolysate supported 50 % fishmeal replacement and reduced eFIFO by 31 %.