Effects and mechanism of micro-nano bubbles on high density live transport of Litopenaeus vannamei

This study aimed to investigate the effects of micro-nano bubble (MNB) water on the survival rate of Litopenaeus vannamei during high density live transport and its physiological mechanism, in order to provide new insights and technical support for the live transport of aquatic products such as shrimp. The water used in high density transport under ecological ice temperature (13 ℃) was treated with MNB technology. Control groups included a low density group (LDG) and a high density group (HDG) under ecological ice temperature without MNB treatment. This study systematically investigated the effects of MNB technology on the water quality of transport water, survival rate, energy metabolism, respiratory metabolism, oxidative stress and immune-related indicators of Litopenaeus vannamei, so as to explore the interactive regulatory mechanism of MNB technology on energy metabolism and antioxidant system during live transport. MNB significantly improved the survival rate of Litopenaeus vannamei under ecological ice temperature and high density transport conditions. After 24 hours of transport, the survival rate reached 86.49%, representing an increase of 14.28% compared to the high density group under ecological ice temperature alone. MNB effectively improved water quality by inhibiting the total bacterial count, increasing dissolved oxygen (DO) content, and slowing the trend of water quality deterioration. It also alleviated hepatopancreas damage, maintained cellular structural integrity, and ensured normal mitochondrial function, thereby supporting normal respiratory metabolism. In terms of metabolism, MNB delayed the time to peak lactate levels, enhanced lactate dehydrogenase (LD) and lactic dehydrogenase (LDH) enzyme activities, and promoted the aerobic respiration process. By reducing glucose (GLU) consumption, the hemolymph GLU content decreased from 2.32 mmol/L to 0.35 mmol/L in the MNBG, while it decreased to 0.21 mmol/L in the HDG and 0.26 mmol/L in the LDG. The HDG showed the most significant consumption, with a significantly lower concentration at 24 h compared to the MNBG and LDG (P<0.05). Furthermore, MNB up-regulated hexokinase (HK) and pyruvate kinase (PK) enzyme activities and their related gene expression levels, activated AMP-activated protein kinase-alpha (AMPK-α) gene expression, and initiated the AMPK signaling pathway, thereby regulating energy metabolism to counteract oxidative stress. In terms of antioxidant capacity, MNB inhibited the production of malondialdehyde (MDA), reduced oxidative damage, and enhanced the body's antioxidant defense by increasing catalase (CAT), total antioxidant capacity (T-AOC), and superoxide dismutase (SOD) enzyme activities. Meanwhile, the activities of immune enzymes such as alkaline phosphatase (AKP) and acid phosphatase (ACP) exhibited a gradual decreasing trend, with the time to reach the maximum value varying among different preservation groups. Owing to the dissolved oxygen enhancement and stress-alleviating effects of MNB, the cold and extrusion stress on Litopenaeus vannamei was reduced, and this change contributed to the maintenance of the normal immune function of the shrimp. This study demonstrated that MNB can activate the AMPK signaling pathway, reshape the energy metabolism balance of shrimp, promote aerobic metabolism, and significantly reduce lactate accumulation and excessive glycogen consumption. It maintained the efficient scavenging capacity of SOD and T-AOC in the hepatopancreas, inhibited the accumulation of the lipid peroxidation product MDA, and thus alleviated oxidative stress damage to the hepatopancreas. By stabilizing the dynamic balance of immune enzymes ACP and AKP in hemocytes, MNB ultimately improved the survival rate of shrimp under high density transport conditions. This study provides a theoretical basis and practical reference for the innovation of fresh aquatic products transportation technology, and provides a broad prospect for MNB in the preservation and transportation of aquatic products.