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¹ Bilecik Seyh Edebali University, Faculty of Science, Department of Molecular Biology and Genetics, Bilecik, Turkey, 11230
² Ege University, Faculty of Science, Department of Biology, Izmir, Turkey 35100 DOI : 10.4194/TRJFAS28324 Viewed : 147 - Downloaded : 131 Algae have attracted increasing interest as feed additives in fish farming. In this study, Stypopodium schimperi, which was determined to have 81.39±0.88% ROS effect (X±SD) by DPPH test among representatives of three macroalgae classes, was used as a fish feed supplement. The algal extract showed 9-11 mm inhibition zones against tested pathogenic strains in disk diffusion experiments. In broth dilution tests, the highest antimicrobial efficacy was observed at a 1/16 dilution against E. coli ATCC 25922. The effects of the algae, incorporated into fish feed at a 5% concentration, on gut microbiota were assessed using 16S rRNA amplicon sequencing. Alpha diversity among groups was determined by Shannon and Simpson indices, while beta diversity was obtained by Principal Coordinate Analysis (PCoA) based on Bray-Curtis distance matrices. The PCoA1 (81.13%) and PCoA2 (18.85%) axis separates group A (experimental group) from CI (day 0 control group) and CF (day 21 control group). This indicates that the microbial community structure of sample A is fundamentally different from the other two, and the microbial profile between CI and CF is relatively close. Notably, in the Group A, Pseudomonadaceae (75.31%) and Moraxellaceae (21.57%) were the most abundant bacterial families, whereas in the CF group, Rhodobacteraceae (36.34%), Enterobacteriaceae (11.66%), and Pseudomonadaceae (6.78%) predominated. The CI group, was primarily characterized by Enterobacteriaceae (35.08%), Rhodobacteraceae (26.55%), and Pseudomonadaceae (4.8%). While algae supplementation inhibited various pathogens, a significant increase in the genus Pseudomonas was observed. Overall, the addition of S. schimperi to fish feed induced notable changes in gut microbiota composition and led to a statistically significant improvement in the fish`s Specific Growth Rate. Keywords : Macroalgae Metagenome analysis Zebrafish