Studies on the mechanism of occurrence and, the influence on breeding performance in mosaic fish and shellfish from the viewpoint of genetic conservation

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1) In masu Salmon embryos, subjected to the treatment with hydrostatic pressure to inhibit the first cleavage, delayed and aberrant cell divisions probably due to the formation of multipolar sindle, fragmentation of chromosomes and other factors were observed. The occurrence of inviable mosaic embryos was caused by these abnormalities.2) Masu salmon developed from the treatment for tetraploidization by inhibition of the first cleavage frequently exhibited diploid-tetraploid mosaicisms in various organs and tissues. When diploid-tetraploid salmon had gonads including germ cells originated from tetraploid blastomeres, functional diploid gametes were generated. Mass production of triploid progeny was successfully realized by the cross between normal and mosaic parents.3) Although haploid embryos were inviable in fish, infrequent spontaneous haploid-diploid mosaics often exhibit the recovery of survival potential. The recovery of survival capacity by adding diploid cells to haploid embryos was experimentally confirmed by the production of viable haploid-diploid goldfish chimeras, which were induced by transplantation of blastodisc.4) In wild populations of crucian carp and loach, a few mosaic individuals were found out. Diploid-triploid mosaic loaches were disclosed to generate fertile unreduced diploid sperm, which were genetically identical, i.e. clonal. The occurrence of haploid-diploid, diploid-tetraploid and other mosaics was also observed in aquaculture farm and egg quality was considered as a cause of mosaicism.5) Triploid abalone were induced by inhibition of the second polar body release after fertilization and their ploidy status was studied for two years. Diploid-triploid mosaicism was exclusively detected in epipodial tentacle tissues and ploidy Status was changed from triploid to diploid or vice versa. However, no such alteration was not seen in other tissues.