Survival Traits of Naturalized, Hatchery, and Hybrid Strains of Anadromous Rainbow Trout during Egg and Fry Stages

Abstract

Two strains of anadromous rainbow trout Oncorhynchus mykiss, naturalized steelhead and “kamloops” (not the pure Kamloops strain from British Columbia, hence not capitalized) currently inhabit the Minnesota waters of Lake Superior and may have the potential to hybridize. This could compromise the genetic integrity of the naturalized steelhead population. Both strains are supplemented by annual stocking, despite the fact that the steelhead population reproduces naturally. Egg viability and fry behavior experiments were undertaken to evaluate the potential for hybridization and to provide information for future management of the two strains. The kamloops eggs were slightly smaller, but sizes overlapped substantially with steelhead egg sizes. Mortalilty of kamloops eggs from spawning to hatching was greater than steelhead eggs. Steelhead fry exhibited a greater fright response (wariness) than kamloops fry when startled by movement over their tanks. Hybrid egg survival and wariness traits were intermediate to those of the pure strains, but more closely resembled those of the maternal strain. These traits appeared to be heritable. Reevaluation of steelhead and kamloops management will be necessary in the future, taking into account the popularity of the kamloops fishery and the potential for degradation or elimination of the naturalized steelhead strain.