Conventional protein sources in aquafeeds, such as fishmeal and soybean meal, raise environmental and ethical concerns, prompting the search for sustainable alternatives. White lupin meal has yielded promising results, but its long-term effects on Siberian sturgeon remain insufficiently studied. In a 540- day experiment, juvenile sturgeons (initial weight: 3.9 ± 0.3 g) were divided into four dietary groups: a soybean-based reference (R), a fishmeal-based control (L0), and two lupin-supplemented groups (L5: 5%, L10: 10%). Basic rearing indices were assessed, followed by other analyses: body proximate composition, histological and immunohistochemical evaluation of digestive organs, enzymatic activity, and oxidative stress markers. All analyses were performed in triplicate. Despite significantly lower final weight in group L10, meat of this fish contained the highest protein and the lowest fat contents. Histological analyses revealed a significant shortening of intestinal folds in the spiral intestine in group L5, while group R showed the strongest immune activation, evidenced by a high number of intestinal CD3-positive cells. Enzymatic profiles indicated impaired antioxidative mechanisms in lupin-fed groups. The findings suggest that lupin meal can be incorporated into Siberian sturgeon diets, although further studies are required.