Effects of the ratio of commercial feed to mixed microalgae on metamorphosis, physiological health, and related gene expression in Penaeus vannamei larvae

High-quality shrimp seedlings are the lifeline of the Penaeus vannamei industry, but their production is often limited by unstable and expensive living microalgae. To develop a more sustainable larval rearing strategy, this study systematically evaluated the effects of co-feeding strategies on metamorphosis, physiological health, and molecular regulation of P. vannamei from nauplius IV stage to mysid I stage by establishing a gradient of commercial feed to microalgae ratios from 0 to 100%. The results showed that increasing the proportion of commercial feed significantly improved larval survival and reduced malformation rate ( P < 0.05), but also led to slower metamorphosis and growth rate. High proportions (≥80%) also induced significant oxidative stress and suppressed key immune functions. Interestingly, molecular compensation was observed in the 100% commercial feed group: although enzyme activity was inhibited, the expression of immune-related genes was significantly upregulated ( P < 0.05). Overall, the 40% feeding ratio (C40) showed the best performance, with the highest pepsin and superoxide dismutase (SOD) activities ( P < 0.05), while maintaining stable growth and physiological homeostasis. These results indicate that a 40% co-feeding ratio is the optimal strategy for balancing high survival with maintaining the growth quality and physiological health of shrimp larvae. This finding provides important scientific evidence for developing sustainable rearing programs for P. vannamei hatcheries.