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

## TL;DR

Adding Lactobacillus plantarum to the diet of red claw crayfish improves muscle amino acids, immune function, and lipid metabolism, with 1.0 g/kg being the best amount.

## Contribution

This study identifies the optimal dietary level of Lactobacillus plantarum for improving lipid metabolism and immune indices in red claw crayfish.

## Key findings

- L. plantarum increased essential and non-essential amino acids in crayfish muscle.
- L. plantarum reduced saturated fatty acids and improved hemolymph immune and metabolic indices.
- L. plantarum upregulated lipid metabolism and inhibited the mTOR pathway in crayfish.

## Abstract

Red claw crayfish (Cherax quadricarinatus) is a valuable freshwater economic crustacean, yet its aquaculture is limited by unstable seedling supply and lipid metabolism disorders, while the regulatory mechanism of Lactobacillus plantarum on this species remains unclear. This study conducted a 56-day feeding trial on juvenile crayfish (0.13 ± 0.01 g) with four diets containing 0, 0.10, 1.00 and 10.00 g/kg L. plantarum. Results showed L. plantarum increased muscle amino acids, reduced saturated fatty acids and improved hemolymph immune and metabolic indices. It also upregulated lipid metabolism and inhibited the mTOR pathway in crayfish. Notably, 1.0 g/kg was the optimal supplementation level.

The objective of this research was to examine how varying dietary inclusion levels of Lactobacillus plantarum influence the muscle composition, hemolymph biochemical indices, lipid metabolism, and the mTOR signaling pathway in red claw crayfish (Cherax quadricarinatus). Four diets with 0 (CK), 0.10 (LG), 1.00 (MG), and 10.00 (HG) g/kg L. plantarum 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 (p > 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 (p < 0.05), while total saturated fatty acids showed no significant variation among all groups (p > 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 (p < 0.05). Lipid metabolism was upregulated, and the mTOR pathway was inhibited in experimental crayfish (p < 0.05). This study demonstrates that dietary L. plantarum enhances lipid metabolism in red claw crayfish, with 1.0 g/kg L. plantarum identified as the optimal supplementation level.