Effects of Dietary Astragalus membranaceus and Atractylodes macrocephala Extracts on Juvenile Red Swamp Crayfish (Procambarus clarkii): Possible Associations Among Intestinal Microbiota Homeostasis, Digestive Enzyme Activity, Oxidative Stress, and Gr

Astragalus membranaceus and Atractylodes macrocephala are traditional Chinese medicinal herbs known for their potential anti-inflammatory and immunomodulatory properties; however, their effects on the growth performance, muscle composition, and intestinal microbiota of aquatic animals remain poorly understood. A total of 480 healthy juvenile red swamp crayfish (Procambarus clarkii) with uniform size (initial mean body mass 5.24 ± 0.04 g) were randomly assigned to four isonitrogenous diets containing 0, 250, 500, and 750 parts per million (ppm) of an Astragalus–Atractylodes extract (three replicates per treatment, 40 individuals per replicate) and fed for six weeks. After a 24 h fasting period, crayfish were randomly sampled for subsequent analyses. Results were as follows: (1) There were no significant differences in the final weight, specific growth rate, meat content, hepatosomatic index, intestinal length index, or condition factor among all groups of crayfish (p > 0.05). (2) The crude lipid content in crayfish muscle was significantly lower in all treatment groups compared to the control group (p < 0.05), whereas no significant differences were observed among groups in terms of muscle moisture, crude protein, and ash contents (p > 0.05). (3) Compared with the control group, the activities of glutathione peroxidase (GPX) and catalase (CAT) in the 750 ppm group were significantly increased, while the content of malondialdehyde (MDA) was significantly decreased (p < 0.05). (4) The intestinal microbiota of Procambarus clarkii was dominated by Firmicutes, Proteobacteria, and Actinobacteriota. Dietary Astragalus membranaceus–Atractylodes macrocephala extracts altered community composition, decreasing the relative abundance of opportunistic genera such as Pseudomonas and Mycobacterium and, to some extent, improving co-occurrence network stability. (5) Correlation analyses linked host phenotypes to key differentially abundant genera: final weight was associated with Bosea and Nannocystis, hepatosomatic index and meat content with Nannocystis and Pseudomonas, respectively, and lipase activity with Pseudomonas, Nannocystis, and Bosea (p < 0.05). GPX was associated with Pseudomonas and Mycobacterium (p < 0.05), whereas MDA showed only weak associations with these genera but was negatively correlated with growth performance indices (p < 0.05). Overall, dietary Astragalus–Atractylodes extracts enhanced antioxidant capacity, tended to increase intestinal lipase activity, and significantly altered gut microbial community composition of P. clarkii, including reduced relative abundance of selected putatively harmful taxa and altered inferred microbial association patterns; under the present conditions, 750 ppm produced the most favorable overall response among the tested supplementation levels.