In the present study we take advantage of a large-scale common garden experimental setup in the wild to examine gut microbial community assembly and development in Atlantic Salmon. In a natural river environment, we examined the gut microbiome of Atlantic Salmon parr sampled over a 10-month periodWe examined the role of different drivers of microbial assembly including abiotic variables (e.g. water temperature) host genetics, as well as water and feed-associated microbiota on the structure of the gut microbial community. In addition, we utilized abundance-occupancy distributions to evaluate the importance of stochastic colonisation processes in the assembly of the gut microbial community. . By exploring the intricate interplay between stochastic and deterministic factors driving community assembly, our study offers a comprehensive perspective on the ecological succession of the wild gut microbial community in juvenile Atlantic Salmon's microbiome