Effect of triploidy on growth and survival of pre-smolt and post-smolt coho salmon ( Oncorhynchus kisutch)

Growth and survival was monitored in full-sib diploid and triploid coho salmon families held at elevated temperature and accelerated photoperiod to induce them to smolt as underyearlings. At tagging, the diploids were significantly heavier than the triploids. After tagging, the diploid and triploid fish were reared in individual family tanks for another month before being combined into pooled groups for acclimation to salt water and transfer to seawater net pens. Diploid and triploid pre-smolts grew at the same rate over this period of acclimation to sea water. By the time of transfer to seawater net pens, the diploids were still slightly larger than the triploids, although the difference was not significant. The triploid post-smolts grew as well as the diploids throughout the first summer of seawater rearing. As a result, there was no significant difference in weight between diploids and triploid post-smolts by the following October. The growth of triploids relative to diploids was not consistent among families, resulting in a significant interaction of family and ploidy for weight, growth rate and condition factor. It is concluded that when triploid coho salmon are reared in a favourable environment, their performance is comparable to that of diploids during the smolt and post-smolt stages.