Impact of Body Weight on the Intestinal Microbiome of Cage‐Cultured Oyster Pompano ( <i>Trachinotus anak</i> )

Oyster pompano (Trachinotus anak) is a commercially valuable marine species widely farmed in Southeast Asia, yet growth heterogeneity remains a persistent challenge in cage aquaculture. To investigate whether body weight influences the intestinal microbiota of this species, we compared the gut microbial communities of small and large T. anak using high-throughput 16S rRNA gene sequencing. The intestinal microbiota was dominated by Pseudomonadota (Proteobacteria) and Mycoplasmatota, together accounting for nearly 80% of total sequences, with additional contributions from minor phyla such as Spirochaetota, Thermodesulfo bacteriota, and Bacteroidota. While alpha- and beta-diversity analyses revealed no significant differences between groups, community composition and structure varied. Smaller fish harbored a more heterogeneous assemblage at the class level and a broader suite of core taxa, including Acinetobacter, Aeromonas, Bdellovibrio, and Comamonas. In contrast, larger fish were dominated by fewer classes, with Photobacterium and Brevinema emerging as distinctive core members. LEfSe analysis identified discriminant taxa between groups, although these trends were not statistically significant after multiple-testing correction. Network analysis highlighted striking differences in microbial interactions: smaller fish exhibited highly modular, densely connected networks with potential keystone taxa such as Paracidovorax and Ensifer, whereas larger fish displayed simpler, less structured networks indicative of reduced ecological stability. Together, these findings demonstrate that body weight is associated with subtle but ecologically meaningful shifts in microbiota composition, core membership, and interaction networks in cage-cultured T. anak. This work underscores the potential of microbiome-informed management strategies to mitigate growth variability and enhance the sustainability of marine aquaculture.