Five hundred and ninety two Siberian sturgeon (A. baerii) fingerlings (average weight, 11.1±0.9 g) were randomly distributed in 16 tanks (150 L) at a density of 35 fish per tank and fed different treatments (Control, degrading bacteria, 2% PHB, degrading bacteria + 2%PHB) for 60 days. At the end of the experiment, the results indicated that the fish fed PHB or bacteria treatments had low midgut pH and the lowest pH was observed in PHB treatment. Also PHB significantly decreased hindgut pH then the others and the lowest hindgut pH was seen in PHB treatment (p<0.05). Dietary treatments affected on the lipid metabolism in fish muscle and liver and no significant difference was observed in case of saturated, monoenoeic and total omega 6 fatty acids in fish muscle whereas the fish fed PHB with bacteria showed low linolenic acid, EPA, DHA and total omega 3 then the others.  The results in this experiment show that PHB have beneficial effects on digestive tract pH while do not change muscle omega 3 fatty acids and can be candidate as new product in aquaculture.