Triploid incubation and growth performance: comparison of meiotic and interploid triploid rainbow trout (Oncorhynchus mykiss) inter- and intrastrain crosses

Abstract

Salmonids undergo major physiological changes during maturation critical for the reproductive success of this group; however, this also causes a marked degradation in the commercial value of the carcass. Aquaculturists have attempted to mitigate the effects of maturation in a variety of ways. Induction of triploidy, the presence of three chromosome sets, has been found to produce sterile fish.Overall, the growth of triploid fish prior to maturation has been significantly inferior to diploid fish, however, genetic selection may be a potential method to improve the performance of triploids. The relationship between genetic composition and induced polyploidy was examined in several strain hybrids of rainbow trout (Oncorhynchus mykiss) during 1988 and 1989. Triploidy was induced via retention of the second polar body using a thermal shock (meiotic triploids) and tetraploid-diploid crosses (interploid triploids). Comparisons were made between the triploid types and diploid controls with emphasis on incubation and juvenile life history.Meiotic and interploid triploids exhibited high mortality rates during incubation, but in the case of the interploids this was due to poor fertilization, 5-40% fertilization success. Whereas, in the meiotic triploids this was due to developmental aberrations. In general, there were no differences in the embryonic growth rates of diploids and triploid embryos within each cross; however differences between crosses were apparent.The growth of the different triploid types after ponding varied depending, in part, on the specific cross produced. Meiotic triploids experienced a retardation in growth during the first 60 days after ponding relative to their diploid controls. In the period of 60-120 days, the growth rate of specific meiotic triploid crosses improved considerably such that they were indistinguishable from diploids. Interploid triploids were exhibited growth rates that were indistinguishable from diploid controls, with one exception in 1989 where the interploid cross significantly outperformed its control.The importance of genetic composition and method of triploid induction strongly suggested that judicious selection of parental strains and individuals within those strains could produce improvements in the growth rate of triploids. Furthermore, the interploid crosses appeared to be the more effective method of triploid production.