Impact of Dietary Lactobacillus plantarum on Muscle Composition, Hemolymph Biochemistry, Lipid Metabolism, and the mTOR Signaling Pathway in Red Claw Crayfish (Cherax quadricarinatus)

The objective of this research was to examine how varying dietary inclusion levels of <i>Lactobacillus plantarum</i> influence the muscle composition, hemolymph biochemical indices, lipid metabolism, and the mTOR signaling pathway in red claw crayfish (<i>Cherax quadricarinatus</i>). Four diets with 0 (CK), 0.10 (LG), 1.00 (MG), and 10.00 (HG) g/kg <i>L. plantarum</i> were formulated, with three replicates of 40 crayfish (average weight: 0.13 ± 0.01 g, average length: 0.58 ± 0.01 cm) in a 56-day trial. Results showed that no significant differences in muscle crude protein, crude lipid, ash, or moisture were observed between experimental and CK groups (<i>p</i> > 0.05), while the contents of multiple essential amino acids (e.g., arginine up to 6.05%, histidine up to 7.52%) and non-essential amino acids (e.g., aspartic acid up to 3.70%, glutamic acid up to 1.76%) were significantly elevated, and the content of muscle C18:0 (a saturated fatty acid) was notably reduced (<i>p</i> < 0.05), while total saturated fatty acids showed no significant variation among all groups (<i>p</i> > 0.05). Hemolymph alkaline phosphatase, transaminases, lactate dehydrogenase, and lysozyme activities, as well as glucose, total protein, and albumin levels, were significantly higher in experimental groups (<i>p</i> < 0.05). Lipid metabolism was upregulated, and the mTOR pathway was inhibited in experimental crayfish (<i>p</i> < 0.05). This study demonstrates that dietary <i>L. plantarum</i> enhances lipid metabolism in red claw crayfish, with 1.0 g/kg <i>L. plantarum</i> identified as the optimal supplementation level.