Sturgeon farming requires special attention. In addition to a relatively long rearing, climate change has resulted in increasingly high temperatures favorable to the emergence of pathogens. The control of water quality is essential especially the first years of life of the fish to prevent a mimivirus (AcIV-E) and a mycobacterium (Mycobacterium liflandii). These crises can lead to significant mortality (up to 70%) and have only been documented in hatchery populations where mortality can reach as high as 100 %. Mycobacterium liflandii, fatally affects young generations of Siberian sturgeon (Acipenser baerii) mainly in year N + 1 with mortalities reaching 30 % when river temperatures rise above 21 °C (summer period). The retention of these pathogenic microorganisms and of total flora by ultrafiltration was evaluated at a semi-industrial scale. The first part focuses on the specific removal of mimivirus, total flora and mycobacteria and the second part aims to evaluate over the long term (5 months) the hydraulic performances of the ultrafiltration process. Although the temperature (maximum 21 °C) was not sufficient for the mycobacteria to be detected, a good retention of mimiviruses (up to 4.7 log removal) and total flora was observed throughout the study. A more stable water quality was obtained after ultrafiltration and this work confirms the potential great interest of ultrafiltration for the biosecurity of fish production.