Diet and digestive traits associated with crab digestion in the crab-eating frog (Fejervarya cancrivora)

Despite the mechanical resistance of chitin-rich exoskeletons, how anurans with limited chewing capacity utilize crustacean prey remains poorly understood. The crab-eating frog ( Fejervarya cancrivora ), which inhabits mangrove and brackish-water environments and feeds on crustaceans, provides a suitable model system for addressing this question. However, whether its natural diet is associated with host digestive traits and gut microbial functional potential remains unclear. To address this, we combined stomach-content analysis via stomach flushing with gastrointestinal histology, digestive enzyme assays, and gut metagenomics to examine crustacean consumption in relation to host digestive characteristics and microbial functional potential. The results showed that decapods dominated stomach contents by volume, accounting for 83.50% in males and 92.83% in females. The stomach exhibited prominent longitudinal folds and circular, oblique and longitudinal muscle bundles, consistent with food accommodation, mixing and propulsion. Chitinase activity was detected in the stomach, small intestine and large intestine, indicating chitin-hydrolyzing capacity at multiple gastrointestinal sites. Gut metagenomes harbored genes spanning chitin polymer cleavage, chitooligosaccharide and chitobiose processing, N-acetylglucosamine (GlcNAc) transport, and intracellular metabolism, with distinct candidate source genera at each stage: Plesiomonas and Aeromonas (polymer cleavage), Candidatus Avirikenella and Ruthenibacterium (chitooligosaccharide and chitobiose processing), Cetobacterium (GlcNAc transport), and Mucinivorans , Parabacteroides , and Alistipes (intracellular metabolism). These annotations indicate that genes associated with different stages of chitin utilization are distributed across multiple bacterial genera. Together, these findings associate crustacean consumption in F. cancrivora with host gastrointestinal structural traits, endogenous chitin-hydrolyzing capacity, and a gut microbial gene repertoire with the potential to process chitin-derived compounds, providing new insight into the ecophysiological basis for the utilization of chitin-rich animal prey by F. cancrivora .