Jakimowicz, M.; Sidorczuk, K.; Huyben, D.; Hildebrand, F.; Napora-Rutkowski, Łukasz; Hajduk, P.; Sztuka, M.; Mielczarek, M.; Słomian, D.; Szulc, U.; Jarosz, L.; Szyda, J.

Probiotics are increasingly explored in aquaculture to enhance fish health and growth without leaving harmful residues. However, their efficacy in real-world pond environments remains poorly understood. Here, we conducted a 103-day field experiment to assess the effects of two effective microorganisms commercial products supplementations on microbial communities and growth performance of common carp (Cyprinus carpio). Effective microorganisms were added both to feed and directly to pond water. Microbial diversity was analysed using 16S rRNA and whole-genome shotgun sequencing across three environments - water (three time points), sediment (two time points) and fish intestine (one time point) - from 25 experimental ponds. Bioinformatics processing involved QIIME2 and MG-TK pipeline with taxonomic classification based on the SILVA database. The results showed that although supplemented bacterial families did not establish significantly in pond environments, fish exposed to specific effective microorganisms treatments exhibited improved growth metrics. These findings suggest that effective microorganisms can enhance carp growth in aquaculture without significantly altering resident microbial communities, offering a promising residue-free alternative to traditional additives.