Effects of MS-222 on the physiological and biochemical response, histology, gut bacteria and flesh quality in largemouth bass (Micropterus salmoides)
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This study investigated the effects of MS-222 on various biochemical indices, antioxidant status, nonspecific immune response, histomorphology (gill and liver), gut bacteria, and flesh qualities in largemouth bass ( Micropterus salmoides ). We first evaluated the anaesthetic effects of MS-222 at different concentrations (20, 40, 60, 80, 100 mg/L) on bass (~ 468.34 g) and fish can reach state of deep sedation at 40 mg/L which suitable for liver transportation. Subsequently, the fish were exposed to 40 mg/L MS-222 for 24 h and then transferred to clean water for recovery. Serum, gill, liver, intestine, and back muscle samples were collected at 6, 12, and 24 h post-treated and at the same intervals post-recovery. The results showed that the concentrations of serum cortisol, glucose, LDH, and AST did not significantly change during sedation or recovery periods, although the BUN level significantly increased. The activity of antioxidase was not significantly affected, but the malondialdehyde (MDA) concentration decreased during sedation period. MS-222 induced atrophy and hypertrophy in gill filaments, decreased the nucleolus number, and increased vacuolation in the liver; these changes were not fully reversed by 24 h post-recovery. MS-222 treatment disrupted gut bacteria, reducing the abundance of beneficial bacteria such as Cetobacterium . An increase in flavour substances, such as sweet and umami amino acids, betaine, and nucleotides, enhanced the flavour of the muscle during sedation and recovery periods. Additionally, MS-222 decreased the proportion of monounsaturated fatty acids (MUFAs) and increased the proportion of polyunsaturated fatty acids (PUFAs). Analysis of electronic nose data indicated that MS-222 treatment distinguished the flavor of fish at sedation period, but diminished during the recovery period. This study demonstrates the influences of MS-222 at 40 mg/L on the physiology, biochemistry and flesh qualities of largemouth bass, which provides a reference for the application of MS-222 in live transportation of largemouth bass.