can develop to physiology maturity and exhibit strong secondary sex characters. Conversely, the gonads of female triploid rainbow trout are typically underdeveloped and are characterized by a We evaluated the effect of chromatosome polyploidy on the reproductive potential of triploid male rainbow trout. We obtained hybrid embryos by artificially inseminating diploid female trout with sperm from triploid male rainbow trout. The diploid females were obtained from a superior strain of two generation family selective breeding. The male triploid was obtained by artificially inducing triploidy using heat shock. We monitored the development of the hybrid embryos and measured their DNA content (ploidy) using flow cytometry. The fertility, eyed rate, and hatching rate of hybrid embryos were significantly lower than the control diploid embryos (fry died during early development or within a short time after hatching. There was considerable variation in the DNA content of the hybrid embryos. The to 3n and their DNA content was ~2.5 times that of the control embryos. The ploidy of the remaining 16% ranged from 3n to 4n. Our results suggest that karyoplasm between the gametes of male triploid and femalediploid rainbow trout. We hypothesize that the hybrid embryos do not survive because of disorders of gene expression and regulation.