The authors performed an instantaneous bioenergetic study with rainbow trout ( Oncorhynchus mykiss ) of 206.3 g ± 2.9 g in a group respirometer of nine 250 l tanks at five different water temperatures (12, 14, 16, 18, 20°C) to determine the optimal thermal condition for a maximal visualization of the protein‐sparing effect. Twelve fish per tank were tested at a stocking density of 9.94 kg m −3 ± 0.14 kg m −3 and fed three low‐...