This dataset documents the length and developmental stage of pallid sturgeon and shovelnose sturgeon free embryos from the time of hatch through melanin plug expulsion (the approximate onset of exogenous feeding) reared in the laboratory at a constant temperature. Free embryos from 4 pallid sturgeon crosses and 7 shovelnose sturgeon crosses were reared separately in the laboratory at a mean temperature of 17.8 degrees Celsius (range 17.3–18.4 ). Beginning on the day of hatch, a minimum of three to six free embryos from each cross was randomly sampled and preserved in 10% neutral buffered formalin at 2 to 12-hour intervals, depending on age. Free embryos were microscopically examined and assigned a developmental stage (i.e., 36–45) following those described for Acipenser guldenstadti, A. ruthenus, and A. stellatus by Dettlaff and others (1993) using a suite of selected morphological characteristics and total length was recorded (to the nearest 0.01 millimeter). Time at fertilization was considered the beginning of ontogenetic development for age calculations and accumulation of thermal units. Developmental stages were related to days post-fertilization (DPF) and cumulative thermal units (CTU). CTU are calculated as the sum of water temperature, in degrees Celsius, from the time of fertilization to the time of sample preservation. The onset of the developmental stage for each family cross was defined as the time of sample collection when at least half of the free embryos exhibited the characteristic traits of the specific stage.