Single-cell transcriptomics reveals the hemocyte atlas and molecular mechanisms underlying the growth-immunity...

Individual growth heterogeneity in Litopenaeus vannamei severely constrains aquaculture uniformity and yield, yet the systemic cellular regulatory mechanisms underlying this phenomenon remain elusive. Here, we combined scRNA-seq and weighted gene co-expression network analysis (WGCNA) to systematically compare hemocyte profiles between fast-growing (FG) and slow-growing (SG) groups, to elucidate the cellular and molecular basis of the "growth-immunity trade-off." We identified six major hemocyte clusters and reconstructed a continuous differentiation trajectory spanning from progenitor-like cells (Cluster 5/0) through a high-metabolic biosynthetic transition state (Cluster 1/3) to mature immune effectors (Cluster 2/4). Pseudotime analysis indicated divergent hemocyte distribution patterns between the two groups: FG hemocytes were predominantly enriched near the trajectory origin (Cluster 5), a population characterized by high expression of tissue development-related genes. In contrast, cells from the SG group were shifted toward the intermediate and terminal stages, showing specific enrichment in the energy-demanding "biosynthetic" subpopulation (Cluster 3). Differential expression analysis showed that Cluster 3 cells in the SG group significantly upregulated mitochondrial complex I subunit (Ndufs3), oxidative phosphorylation, the TCA cycle, and ribosome pathways, exhibiting typical characteristics of high immuno-metabolism. WGCNA further uncovered the upstream regulatory networks driving this trade-off: the FG group systematically activated the dark-orange module (centered on IRS1 and CCND1), which synergistically maintains progenitor reserves via mTOR and insulin signaling. Conversely, the SG group showed higher activity of the turquoise module, characterized by aminoacyl-tRNA biosynthesis and the expression of the antimicrobial peptide Crustin in progenitor-like cells, suggesting a stress-associated immune activation state. These findings suggest that slow growth may be associated with a transcriptomic shift from progenitor-like states toward energetically demanding immune-related states, providing a cellular hypothesis for the growth-immunity trade-off in L. vannamei. These findings provide a novel cellular perspective on crustacean growth traits and identify key molecular targets for breeding superior strains that balance disease resistance and growth.