Microbial succession accompanies increased antibiotic resistance risk during grass carp (Ctenopharyngodon idella) spoilage under ambient household conditions.

Understanding fish spoilage mechanisms under household storage conditions is critical for food safety in regions with limited cold chain infrastructure, where ambient storage remains common practice. This study investigated the spoilage dynamics, microbial succession, and antibiotic resistance gene (ARG) proliferation in grass carp stored under simulated household conditions at 13.0 ± 3.4 °C using three packaging scenarios. The biogenic amine index (BAI) of fish exceeded 50 mg/kg within 16 h, marking early spoilage onset. After 64 h, K-values surpassed 60%, TVB-N exceeded the safety limit of 20 mg/100 g, and BAI reached over 220 mg/kg, indicating advanced spoilage. 16S rRNA amplicon sequencing demonstrated dramatic microbial community shifts from Cyanobacteriota-dominated fresh samples to Pseudomonadota-dominated spoilage communities, with Aeromonas emerging as the primary specific spoilage organism (SSO), increasing from 0.001% to 67.2% at 64 h. Pathogen abundance escalated from 0.06% to 72.2% in muscle tissues, posing substantial food safety risks. Distinct microbial community structures were observed across tissue types (muscle vs. gut) and packaging treatments, with storage time exerting the strongest selective pressure on community composition. Metagenomic analysis revealed progressive ARG enrichment, with surface samples exhibiting 2.6-fold higher total ARG abundance and 3.8-fold greater ARG type richness compared to the fresh gut baseline by 24 ~ 64 h. Rapid ARG enrichment was detected during early spoilage (24 h), representing a critical food safety concern. Notably, carbapenem resistance genes (e.g., OXA-12, cphA6) were substantially enriched, underscoring the high risk posed by these clinically relevant resistance genes. These findings demonstrate that grass carp stored under ambient household conditions maintain acceptable quality for < 16 h, necessitating immediate consumption or cold chain implementation to ensure food safety and minimize ARG dissemination.