Reproductive Condition of Spotted Bass and Golden Redhorse in a Free-Flowing and a Regulated Tributary of the Lower Missouri River

Photoperiod, temperature, and discharge are cues for fish reproduction.  Dams modify discharge and water temperature, potentially affecting fish reproduction.  Our study determines whether two abundant fish species, spotted bass (Micropterus punctulatus) and golden redhorse (Moxostoma erythrurum), have different spawning timeframes in the regulated Osage River compared to the unregulated Gasconade River, two tributaries of the Lower Missouri River.   Fish were collected by boat electrofishing February through July 2013 from the Missouri River confluence to river mile 12 on the Gasconade River and river mile 20 on the Osage River.  Gonads were collected from fish greater than 200 millimeters to determine sex and reproductive condition.  The Osage and Gasconade had similar male to female ratios for both species.  Spotted bass were about 50% female and 50% male whereas golden redhorse were approximately 65% female and 35% male.  Gonadosomatic indices (GSI) were calculated for 71 golden redhorse and 101 spotted bass.  Although water temperatures were typically 2°Celsius cooler and average discharge was 14,400 cubic feet per second higher in the Osage River, GSI scores of the respective species peaked at similar dates in the two rivers.   Understanding fish use of tributaries will contribute to large-scale ecosystem restoration in the Missouri River basin.