Analysis of Scale Growth Characteristics Between Wild and Hatchery Origin Rainbow Trout Collected From Deerfield Reservoir, South Dakota

Deerfield Reservoir, located in the Black Hills of South Dakota, has a naturally recruiting population of rainbow trout.  Additionally, the reservoir is stocked annually with approximately 12,000 catchable (279-381 mm) rainbow trout of three unique strains.  Previous research used scale growth characteristics to differentiate between wild and hatchery origin fish, but moderate overlap existed among circuli measurements of wild and hatchery samples.  Thus, our objective was to evaluate scale growth characteristics of three hatchery rainbow trout strains and wild origin rainbow trout.  We collected scales at McNenny State Fish Hatchery from the three strains of rainbow trout, as well as wild fish (<200mm) from the Deerfield Reservoir system.  We selected one representative scale from each sample and made three measurements: focus to 6^thcirculus, 5^th to 6^thcirculi, and focus to 12^thcirculus.  Statistical analysis was conducted using analysis of variance with a Tukey’s multiple comparison test to identify significant differences between strains and wild origin fish.  Measurements were found to be significantly different between groups from the focus to the 6^thcirculus. We found the wild origin fish to be significantly different than the Shasta and McConaughy strains, but not different than the Erwin-Arlee strain.  This information was of particular interest as previous genetic analysis showed the genetic composition of wild rainbow trout in the system consisted primarily of the Erwin-Arlee strain.