Changes in survival rate and muscle quality of Megalobrama amblycephala in fish bags during the process of keeping-alive

With the development of aquatic logistics industry, China has now formed a live fish transportation system mainly based on high-density live transportation, supplemented by single fish transportation through plastic fish bag filled with oxygenated water. Although keeping-alive with fish bags has the advantages of shortening the transportation intermediate link, improving the survival rate of fish, and promoting the sales of local specialty fish, there is relatively little research on stress response and muscle quality changes in live fish transported with fish bags, which greatly limits the development of this transportation method. In order to promote the development of live fish transportation industry, this study adopts the fish bag to preserve the survival of the blunt snout bream (Megalobrama amblycephala). Firstly, the influence of survival conditions (temperature, fish-water ratio, and water source) on the survival rate was studied, and the optimal survival conditions were determined; then, the changes in blood stress indicators and muscle quality of fish during the keeping-alive process were studied under the optimal conditions. The results showed that when the transportation environment temperature was 10 ^oC, the fish to water mass ratio was 1:3, and the water source was aerated tap water, the fish survival rate was the highest. The survival rates were 90% and 70% at 36 and 48 hours of keeping-alive process, respectively. During the keeping-alive process, the stress indicators in the blood of the bream showed a fluctuating trend. However, overall, the content of cortisol (COR), urea (URA), and malondialdehyde (MDA) increased first and then decreased; the content of lactate dehydrogenase (LDH) first decreased and then increased; the content of superoxide dismutase (SOD) gradually decreased; the content of catalase (CAT), aspartate transferase (AST), and creatinine (CR) gradually increased. In terms of muscle quality, physical indicators such as whiteness value, shear force, and drip loss show an overall trend of first increasing and then decreasing, which was consistent with the formation of pale, soft and exudative (PSE) meat after stress. Compared with 0 hour, the crude protein, lactate, and glycogen content decreased by 19.0%, 27.2%, and 50.0% respectively after 72 hours of keeping-alive process; The nucleotide compounds of freshness (ADP, AMP, IMP) and bitterness (HxR, Hx), as well as the freshness value K, showed an overall increasing trend; the gap between muscle fibers gradually increased with the prolongation of survival time. This study has shown that during the keeping-alive process, fish are subjected to sustained stress, and the intensity of single stress may gradually weaken. The main reason for the deterioration of fish muscle quality may be related to physiological processes such as energy metabolism disorders. This study can provide a theoretical basis for the e-commerce logistics of fish by fish bags. However, further research is needed on how to effectively alleviate the stress response of fish during the transportation, thereby improving survival rate and muscle quality.