Evidence of Successful Natural Reproduction between Brown Trout and Mature Male Atlantic Salmon Parr

Abstract

Abstract Hybridization between Atlantic salmon Salmo salar and brown trout S. trutta is frequently reported, and the role of mature male Atlantic salmon parr has been suspected but never proven. Salmon fry were stocked into a headwater tributary stream of the Connecticut River, where no adult salmon are present. The stream has a self-sustaining population of brown trout. Enzyme electrophoresis revealed the presence of one hybrid (0.81% of the sampled population). The maternal species was identified as brown trout; therefore, the only possibility for the male parent was that it was a mature male Atlantic salmon parr. This is the first direct evidence of parr producing hybrid offspring in a totally natural setting and in the absence of any sea-return salmon.