Research Article Dietary Effects of Lactobacillus plantarum Combined with Galactooligosaccharide on Immunological and Biochemical Parameters, Gut Microbiota, Digestive Enzyme Activity, Body Composition, and Stress Resistance in Narrow-Clawed Crayfish, Pontastacus leptodactylus (Eschscholtz, 1823) Shiva Nedaei , 1 Ahmad Noori , 1 Alireza Valipour, 2 Ali Asghar Khanipour, 2 and Seyed Hossein Hoseinifar 3 1 Department of Fisheries Science, Faculty of Marine Science and Technology, University of Hormozgan, Bandar Abbas, Iran 2 Inland Water Aquaculture Research Centre Iranian Fisheries Science Research Institute (IFSIR), Agriculture Research Education and Extension Organization (ARREO), Bandar-e Anzali, Iran 3 Department of Fisheries, Faculty of Fisheries and Environmental Sciences, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran Correspondence should be addressed to Ahmad Noori; nooryahmad@gmail.com Received 18 October 2022; Revised 19 February 2023; Accepted 21 February 2023; Published 4 March 2023 Academic Editor: Erchao Li Copyright © 2023 Shiva Nedaei et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The effects of galactooligosaccharide (GOS) and varying levels of Lactobacillus plantarum (LP) on some physiological parameters as well as air exposure stress resistance in clawed crayfish (Pontastacus leptodactylus) were investigated. During a 97-day trial, 216 crayfish were fed with four experimental diets (in triplicates) including the control diet (without GOS and LP), GLP7 (GOS 2%+LP 10 7 CFU.g -1 diet), GLP8 (GOS 2%+LP 10 8 CFU.g -1 diet), and GLP9 (GOS 2%+LP 10 9 CFU.g -1 diet). At the end of the trial, 26% higher amounts of the total hemocyte count (THC) and semigranular cells (SGC) and 27% higher hyaline cells (HC) were observed in GLP7. A significant improvement in lysozyme value was observed in GLP7 and GLP8. Moreover, superoxide dismutase was significantly higher in GLP9, whereas the catalase (CAT) activity did not change in the experimental groups. Unlikely, plasma glucose levels decreased in all the GLP treatments. In terms of intestinal microbiota, autochthonous lactic acid bacteria (LAB) remarkably increased in all the GLP-supplemented groups, while total autochthonous intestinal heterotrophic bacteria counts (TVC) did not change in GLP-supplemented groups. However, 14 days after switching to the basal diet, no reduction was detected in TVC, but LAB levels decreased in GLP7 and GLP9 treatments. Dietary administration of GLP could beneficially modulate digestive enzyme activity, including protease, lipase, and amylase. Furthermore, higher lipid and gross energy were observed in GLP9. However, GLP-supplemented diets could not improve growth performance parameters. After 24 h subjecting to air exposure stress, although no mortality was detected, crayfish fed GLP-supplemented diets were healthier through enhanced THC, SGC, and HC levels in GLP7 and GLP9 and CAT activity in GLP7 and GLP8. These results proved the positive impacts of dietary supplementation with combined GOS and LP, with GLP8 and GLP9 as optimum diets, on immunochemical parameters, intestinal microbiota, digestive enzyme activity, and stress resistance in P. leptodactylus. Hindawi Aquaculture Nutrition Volume 2023, Article ID 3345916, 13 pages https://doi.org/10.1155/2023/3345916