Integrated oxidative, mitochondrial, and apoptotic responses to ammonia-hypoxia co-toxicity in Macrobrachium rosenbergii muscle.

Ammonia accumulation and oxygen depletion frequently co-occur in intensive prawn farming, yet their combined effects on edible muscle quality and the underlying muscle-specific mechanisms in Macrobrachium rosenbergii remain poorly understood. In this study, juvenile M. rosenbergii were exposed for 7 days to a factorial combination of total ammonia nitrogen (TAN; 0, 2, and 50 mg L⁻¹) and dissolved oxygen regimes (normoxia vs. hypoxia). Survival, muscle composition and texture, histology, oxidative biomarkers (SOD, CAT, GSH, MDA), and gene expression were examined together with RNA-seq-based transcriptomic profiling. Survival declined moderately with increasing TAN under normoxia (100-75 %) but dropped dramatically under hypoxia, reaching only 2.8 % in the high TAN-hypoxia group. Co-stress significantly increased muscle moisture while reducing crude protein and lipid contents, accompanied by pronounced deterioration of hardness, cohesiveness, and chewiness. Histological analysis confirmed progressive myofiber separation and edema under severe exposure. Antioxidant defenses showed a biphasic response: SOD, CAT, and GSH were elevated at moderate TAN but sharply suppressed under high TAN-hypoxia, whereas MDA increased steadily, indicating escalating lipid peroxidation. Transcriptomic profiling revealed strong upregulation of glutathione metabolism genes (e.g., GCLC, GPX4) but consistent downregulation of mitochondrial oxidative phosphorylation and peroxisomal markers (e.g., COX1, SDHA, CAT). Concurrent induction of glycolytic genes (HK, PFK, PK) and apoptotic regulators (CYC, CASP8) indicated metabolic reprogramming and irreversible oxidative injury. Overall, TAN-hypoxia co-stress overwhelms antioxidant capacity, disrupts mitochondrial and peroxisomal function, promotes apoptosis, and ultimately drives severe deterioration of muscle structure and flesh quality. These findings underscore the necessity of coordinated ammonia and oxygen management to protect prawn health and product value in intensive aquaculture.