Diploid and triploid Chinook salmon, Oncorhynchus tshawytscha (walbaum): An exploration of induction efficacy, performance and genomic architecture.

Abstract

Triploid salmon are sterile and thus may comprise part of an overall plan to minimize potential genetic disturbances to wild populations caused by the rearing of farmed fish in open seawater netpens. Despite the potential benefits of sterility, triploids are not widely reared for aquacultural purposes in North America mainly due to variable and inconsistent performance. While triploidization is being explored in an increasing number of species, the effect of triploid ization in chinook salmon {Oncorhynchus tshawytscha) has rarely been investigated. In this study, chinook salmon were triploidized in order to assess 1) the efficacy of two triploid induction techniques 2) the utility of triploid chinook salmon for commercial aquaculture and 3) to develop a description of the genomic architecture of triploids. In Chapter One, a comparative examination of triploid ization success and whole organism performance (survival, growth and the antibody response to vaccination) in diploid, heat-shock induced triploid and pressure-shock induced triploid full-sib family groups was carried out in terms of the effect of treatment, genotype (family) and treatment by genotype (family) interactions. In Chapter Two, a comparative examination of performance (survival, growth, and the lysozyme activity response to vaccination) in terms of the distribution and magnitude of phenotypic variance was carried out using a quantitative genetic framework and a paternal half-sib experimental design. Variance was partitioned into additive genetic and a combined epistasis, dominance and maternal effects component and narrow sense heritability values were calculated.Minimal differences in triploidization success, growth and immune functioning were found between heat-and pressure-shock treated family groups. Although pressure-shock treated fish survived better than heat-shock induced triploids, triploids did not survive or grow as well as diploids. Survival of treatment groups was significantly 11 influenced by treatment and family effects while growth traits and antibody response to vaccination were more strongly influenced by the effect of family. Interaction effects were most prevalent for immune function.Triploidization increased total phenotypic as well as additive genetic variance but this was associated with an unexpected and counter-intuitive decrease in the influence of the non-additive component (combined epistatic, dominance and maternal effects) indicating that triploidy may not have increased the genetic complexity of relationships among alleles or loci and that the primary effect of triploidization was additive and dominant. This was also highly suggestive of an overall ploidy dependent regulation of gene expression.The obvious dichotomy between high and low performing families regardless of treatment/ploidy status, the existence of significant family components for many of the performance variables combined with increased heritability values for the measured traits indicated that selective breeding of diploids for increased tr...