Dietary yeast extract mitigates the negative effects of reduced fishmeal diet on growth and metabolism in mud crab (Scylla paramamosain)

Yeast extract (YE) can serve as a viable substitute for conventional protein sources to fishmeal (FM), and as a functional feed ingredient or additive. This study aimed to investigate its effects on growth performance, antioxidant capacity, non-specific immunity, protein metabolism, and the microstructural development of tissues in mud crab ( Scylla paramamosain ). Total of 144 juvenile crabs (average body weight: 18.71 ± 0.19 g), were randomly allocated into four experimental treatments: control diet group (Control; 30% FM), low-FM diet group (LF; 20% FM), LFYA (20% FM + 0.75% YE), and LFYB (20% FM + 1.50% YE). The results showed that, compared with the control group, the low-fishmeal diet adversely affected the percent weight gain of mud crab, reduced protein deposition and amino acid contents in the tissues, and induced oxidative stress, inflammatory responses, as well as damage to the hepatopancreas and intestinal morphology. YE supplementation, particularly at 1.50%, effectively mitigated these adverse effects by enhancing final body weight, specific growth rate, feed efficiency, and survival. Mechanistically, YE improved antioxidant capacity (GSH-Px, T-AOC, and CAT), modulated immune and inflammatory gene expression ( propo , α-2m , mapk14 , myd88 , and nf-κb ), enhanced muscle protein synthesis and TOR pathway activity ( tor , s6k1 , and myoG ), restored hepatopancreas and intestinal structural integrity, and regulated intestinal amino acid transport ( snat1 , lat3 , pcat , and ylat ). Histological analyses confirmed improved hepatopancreatic and intestinal morphology in YE-supplemented groups. Collectively, these findings demonstrate that YE supplementation in LF diets supports growth, metabolic homeostasis, and tissue health in mud crab, offering a promising strategy for reducing FM dependency in sustainable aquaculture. • Yeast extract (YE) improved growth of mud crab under low-fishmeal diets. • YE alleviated metabolic disorders induced by fishmeal reduction. • Dietary YE enhanced protein deposition and amino acid utilization. • YE reduced oxidative stress and protected hepatopancreatic function. • YE mitigated adverse effects of low-fishmeal diets in Scylla paramamosain.