Ontogenetic development of pallid sturgeon ( <i>Scaphirhynchus albus</i> ) and shovelnose sturgeon ( <i>Scaphirhynchus platorynchus</i> ) from hatch through yolk absorption

Sturgeons have a complex free-embryo period extending from hatch to the initiation of exogenous feeding. Although available for some sturgeon species genus Acipenser, descriptions developmental stages free embryos Scaphirhynchus are lacking. We characterised ontogenetic development pallid (Scaphirhynchus albus) and shovelnose (S. platorynchus) through melanin plug expulsion. The rate was similar between among 4 7 crosses reared separately in laboratory at mean temperature 17.8°C. Free required 18.2 days postfertilisation (DPF; 323.5 cumulative thermal units; CTU) reach expulsion 17.9 DPF (318.3 sturgeon. both showed overlap lengths indicating that length alone is insufficient estimate age. Description provides template develop more sophisticated models incorporating stage age field-collected specimens. Improved estimates may aid identification timing location spawning better inform flow manipulation habitat management actions tailored increase survival early life-stage