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

Growth and survival was monitored in full-sih diploid and triploid coho sal mon families held at elevated temperature and accelerated photoperiod to in duce them to smelt as underyearlings. At tagging, the diploids were signifi cantly 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 s eawater net pens. Diploid and triploid pre-smelts grew at the same rate ove r this period of acclimation to sea water. By the time of transfer to seawa ter net pens, the diploids were still slightly larger than the triploids, a lthough the difference was not significant. The triploid post-smelts grew a s well as the diploids throughout the first summer of seawater rearing. As a result, there was no significant difference in weight between diploids an d triploid post-smelts by the following October. The growth of triploids re lative to diploids was not consistent among families, resulting in a signif icant interaction of family and ploidy for weight, growth rate and conditio n factor. It is concluded that when triploid coho salmon are reared in a fa vourable environment, their performance is comparable to that of diploids d uring the smelt and post-smelt stages. (C) 1998 Elsevier Science B.V. All r ights reserved.