STUDIES ON ANEUPLOID BREEDING IN FISHES

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1. Hyperdiploid loaches: Eggs of normal diploid loach were fertilized with spermatozoa of induced triploid loach, which had been generated by inhibition of the second polar body release after fertilization. The resultant diploid x triploid progeny were aneuploids with chromosome numbers between 51 and 59 and showed lower hatching rate (30%) and higher incidence of abnormality (76%), when compared to control diploid cross (80% hatch, 4% abnormal). DNA flow cytometry revealed that surviving two-month-old fish were hyperdiploid (2.2〜2.5n).2. Hypertriploid loaches: One-year-old progeny of the cross between natural tetraploid female and induced triploid male exhibted external abnormalities such as ill-developed tail, bent body or both. DNA flow cytometry revealed that they were hypertriploids. In one 3.2n aneuploid, the formation of 1.7n spermatozoa was suggested by DNA content of testicular cells.3. Natural aneuploid loaches: Externally normal aneuploids which had two types of supernumerary chromosomes in addition to normal members of the diploid karyotype (2n=50, 10m+4sm+36t) were detected in a laboratory-reared family. Normal-sized supernumerary chromosomes had similar size to the normal members, whereas microchromosomes were also observed. Gill tissues exhibted 0〜3 normal-sized and 0〜4 micro supernumerary chromosornes. Gonadal tissues showed 0〜8 normal-sized and 0〜5 micro supernumerary chromosomes. Meiotic figures contained 25〜27 bivalents with additional 1〜2 univalents and 0〜4 micro chromosomes.4. Haploid-diploid mosaic charr: A live haploid-diploid mosaic charr was found by chance. This individual grew to the adult size but was infertile female. Most cells in blood, liver and spleen were haploid, whereas those in brain were diploid.The results obtained here suggest possibilities of aneuploid breeding in fishes using induced triploid and natural aneuploid individuals as sources of aneuploid gametes.