Gut microbiome reorganization as a signal of physiological acclimation in escaped hybrid grouper (Epinephelus lanceolatus ♂ × E. fuscoguttatus ♀).

The introduction of aquaculture-derived hybrid fishes into natural marine ecosystems raises critical questions regarding their physiological capacity to acclimate to novel environments. The hybrid grouper (Epinephelus lanceolatus ♂ × E. fuscoguttatus ♀), a widely farmed teleost in southern China, has increasingly been reported in coastal habitats following escape events. However, the gut microbiome-associated mechanisms underlying its acclimation to natural conditions remain poorly understood. Here, we compared the gut microbiomes of cultured and wild-caught individuals collected from two coastal regions using 16S rRNA gene sequencing integrated with functional prediction and microbial co-occurrence network analysis. Following their transition to natural habitats, escapees retained some dominant aquaculture-associated genera (Halomonas, Cetobacterium, Photobacterium and Vibrio) and clustered closely with local cultured counterparts rather than rearing condition. Beneath this partial taxonomic stability, however, the significant difference in intestinal microbiome between wild-caught and cultured individuals was manifested in predicted functional pathways and microbial interaction networks, characterized by shifts in immune-related processes, energy metabolism and keystone taxa. These findings indicate that hybrid groupers respond to environmental transition through functional and association-level plasticity rather than simple replacement of the gut microbial community. We propose that this dynamic microbiome rewiring may reflect microbiome-level adjustments associated with environmental transition, offering a microbial perspective on the acclimation of aquaculture-derived fishes to heterogeneous marine environments.