Performance and heterosis in farmed and wild Chinook salmon (Oncorhynchus tshawyacha) hybrid and purebred crosses

This study examined traits in Chinook salmon hybrid and purebred crosses for performance differences between wild and farmed fish, and evidence of heterosis. Chinook salmon from two sources were used as parental stock fish from a commercial salmon farm and fish from a natural population (with an active enhancement program). The study population consisted of farmed and wild purebred families and their reciprocal hybrids. Twelve traits were measured in five areas of performance (survival, saltwater growth, saltwater tolerance, stress response and recovery, and fecundity). Significant cross type effects were found for 5 of the 12 traits, and, generally, the wild purebreds performed best. Notable heterosis (i.e., >1% of the mid-parent values) was demonstrated for nine of the performance traits, with four of those being favourable heterosis. However, none of the heterosis exceeded the performance of the best parental lineage. Individual reciprocal crosses showed greater heterosis, but again generally not useful for breeding programs. The lack of favourable heterosis coupled with its generally small effect when present indicates that crossbreeding for hybrid vigour is of limited utility in Chinook salmon culture. The introduction of novel (wild) genetic material into the farmed population did, however, result in considerable performance improvement in growth-related traits, although a loss in disease survival performance was also realized. The observed differences in performance between the purebred wild and farmed families is likely primarily due to additive genetic variation, since the reciprocal hybrid values were generally not significantly different from the mid-parent value. Although our data do not support the use of crossbreeding as a method for exploiting hybrid vigour in Chinook salmon, we do show that significant improvement in performance may result from the inclusion of "wild" gametes in a breeding program; however, some performance losses may also result. (C) 2004 Published by Elsevier B.V.