Detection of hybrids between masu salmon Oncorhynchus masou masou and amago salmon O. m. ishikawae occurred in the Jinzu River using a random amplified polymorphic DNA technique

Identification of masu salmon Oncorhynchus masou masou and amago salmon O. m. ishikawae was accomplished using a random amplified polymorphic DNA (RAPD) technique. Of 80 primers screened, three primers amplified subspecies-specific fragments (OPA11-1095*, OPB5-1618* and OPD5-2038*). Based on fragment patterns, 33 hybrids were detected among 150 upstream-migrating individuals in the Jinzu River, central Japan, a long-time habitat of masu salmon, to which amago salmon were recently introduced. All of the individuals examined in the 2000-2002 cohorts were identified as F₁ and F _x, as well as pure masu and amago forms. These results indicated continuing hybridization, the genetic pollution of the native masu salmon population by amago salmon possibly being a serious problem in the Jinzu River. Both standard length and body weight in F₁ hybrids tended to be less than in pure masu salmon. However, F_x hybrids showed similar body sizes to masu salmon.