The low feed efficiency may partly contribute to the poor growth performance. As estimated by weight gain, the minimum dietary Cu content in juvenile Russian sturgeon is 6.1 mg kg−1. This value is similar to those reported with other fish species, such as 4.78 mg kg−1 for grass carp Ctenopharyngodon idella (Tang et al., 2013), 5 mg kg−1 for channel catfish (Murai et al., 1981) and 5.36 mg kg−1 for grouper