Biosensor-Based Comparison of Stress Responses in Qingtian Paddy Field Carp (Cyprinus carpio var. qingtianensis) and Xingguo Red Carp (Cyprinus carpio var. singuonensis) Under Acute Shallow Water Conditions

Water depth is a crucial environmental factor influencing temperature, oxygen availability, light intensity, and ultimately the physiology, behavior, and distribution of aquatic animals. This study investigated the physiological responses of two common carp varieties—the Qingtian paddy field carp, a core component of the Qingtian rice-fish co-culture system, and the Xingguo red carp, a typical pond-domesticated species—to extreme shallow aquatic environments (5–20 cm depth). Since traditional blood sampling fails to capture dynamic stress levels, we used a real-time glucose biosensor combined with biochemical assays to continuously monitor stress and adaptive reactions. The results show that the Qingtian carp exhibits superior adaptation to shallow water conditions, marked by higher stress tolerance, faster recovery, and efficient lipid-based energy utilization. These findings highlight the value of biosensor-based approaches in aquaculture and affirm the critical role of the Qingtian carp in sustainable integrated rice–fish systems. The domestication of common carp in rice paddies (5–20 cm depth) is challenging, as the fish must withstand drastic fluctuations in temperature and dissolved oxygen, restricted movement, and bird predation without the option of diving. The effects of stress responses in different species of carp in shallow-water environments remain poorly understood, particularly with fluctuating water levels where real-time monitoring is challenging. This study employed a glucose biosensor system enabling real-time monitoring, together with biochemical analysis techniques capable of evaluating multiple physiological indicators, to investigate shallow-water adaptation in Qingtian paddy field carp and Xingguo red carp. Our results quantitatively reveal, for the first time, the differing physiological stress thresholds of the two carp strains under shallow water. The Qingtian paddy field carp exhibited a higher tolerance to shallow water and showed faster recovery from prolonged stress. Furthermore, the total cholesterol and triglyceride contents of Qingtian paddy field carp gradually increased with prolonged shallow-water stress, reflecting the activation of lipid metabolic pathways. These findings highlight the advantages of biosensor technology in aquatic stress research and a strong support of the core element of paddy domesticated carp in the Globally Important Agricultural Heritage Systems.