Induced Allotriploidy in Inviable Interfamilial Hybrids, Female Loach x Male Goldfish and Female Loach x Male Minnow

ドジョウ科とコイ科間の交雑種ドジョウ雌×キンギョ雄およびドジョウ雌×タモロコ雄では、生じた仔魚のほとんどは体躯の矮小、湾曲等の奇形を示し、摂餌に到らず死亡した。例外的に生存した個体はすべてドジョウとなった。染色体観察の結果、前者はドジョウ(2n=50, 10m+4sm+36st, a)とキンギョ(2n=100, 12m+36sm+52st, a)の中間の染色体数(2n=75)と核型(11m+20sm+44st, a)を示し、両親種の染色体を1セットづつもつ二倍性雑種であった。後者もドジョウとタモロコ(2n=50, 12m+32sm, st+6a)の中間の核型(2n=50, 11m+21sm, st+18a)を示したことから、二倍性雑種と判定できた。交雑の直後、低温あるいは圧力処理を加え第2極体放出阻止を試みた。染色体観察よりこれら処理より生じる胚の多くは異質三倍体であることが判った。異質三倍体化により、奇形の程度は緩和されたが、生残個体は得られなかった。Interfamilial hybridizations between female loach Misgurnus anguillicaudatus and male goldfish. Carassius auratus and those between female loach and male minnow Gnathopogon elongatus elongatus gave rise to inviable larvae with abnormal appearances and no survivors appeared. Karyological analyses on these hybrid embryos revealed that they were typical diploid hybrids comprising both maternal and paternal chromosomes. Cold or hydrostatic pressure treatments were made to inhibit the second polar body release after the hybridization. Chromosome observations demonstrated that most embryos developed from the treatments were allotriploidy having two sets of maternal chromosomes and one set of paternal chromosomes. External deformity of the hybrids seemed to be improved by allotriploidization, but no survivors were obtained